AR-15/M16 (Home Workshop Guns for Defense and Resistance)

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The top of this box, which fits against the bottom of the receiver, should be filed to match the contour of the receiver as closely as possible so that when the takedown bolt is drawn up tight, the two pieces will fit together closely, keeping the joint as dust and dirt-proof as possible. The length of these is not crit- A trigger and sear housing may be formed by bending one-eighth inch sheet stock to shape.

However, it may be considerably easier to saw or grind one side of a section of angle iron bed frame material is ideal for this to the proper width and then to weld a flat piece to the side. This will form a box shape which should be left open at the top. The inside dimensions of this housing should be five-eighths inch wide by one inch deep with a finished length of eight inches.

Make it at least eight and one-fourth 8. Weld a plate of the same material across one end to form the rear end of the trigger housing. Beginning two and five-eighths 2. If no tubing is available, a three-eighths inch hole may be drilled lengthwise through either round or square stock to obtain the two needed pieces. The wall thickness should be at least three-thirtyseconds inch, since these will take a considerable beating when the stock is in the extended position.

When the two sections of tubing, which we will refer to as stock retainers, are completed, the trigger housing should be clamped in its finished position against the receiver. Then place the stock retainers in position, the rear end flush with the back end of the trigger housing and the upper side nestled against the receiver. When located in this position, they may be tack welded, with the trigger housing separated from the receiver.

Weld the two retainers securely in place, but only to the trigger housing. A hole, one-half inch in diameter, must be located two and three-fourths 2. These measurements are for the center of the hole, naturally. Carefully drill this hole completely through both sides, making sure that it is square with the housing, since the fire selector mechanism will be located at this point. The trigger should be made from three-eighths inch flat stock of high quality steel, capat: It may be formed by drilling interconnecting holes around the outline and filing to shape as previously described, or it may be sawed and bent to shape from a piece three-fourths inch wide by three-eighths inch thick by four inches long.

Following that, drill a one-fourth inch hole approximately one-fourth inch deep in the bottom side about half way between the pivot pin hole and the trigger nose.

Home Workshop Vol 5 AR 15, M 16 Bill Holmes Paladin Press

The upper portion of a trigger spring will be located in this hole. The trigger nose should be shaped as shown in the drawing. Since this is the part of the trigger that engages the sear with a close, precise fit, it should only be rough shaped at this time. It should not be finished until the sear is completed.

The fire selector that is, the switch to select either full automatic, in which the gun will continue to fire as long as the trigger is held down, or semi-automatic in which case a single round will be fired with each pull of the trigger as well as the trigger pivot pin should be made from round stock as indicated in the drawing. Turn both sides to size and shape them into one piece. Enlarge the ho1e In the rlght hand secUon to. Rotating the fire selector switch degre. A piece one inch wide and three inches long is required and srould be of quality tool steei.

It should be sawed, ground, and filed to the shape shown. The portion wh ch projects into the receiver and engages thE! It will have less drag, resulting in an easier trigger pull, if it. However, it would also have less strength, so I suggest you leave it at three-eighths inch. Establish a center two and one-fourth 2. Place a close fitting steel plug m this hole and drill another hole one-eighth inch forward of the center of the first hole centered on the seam between the plug and rim of the first hole.

If th1s is properly done, the remainder of the plug will form a radiused slot when removed. This will allow the sear to slide forward and backward one-eighth inch over a one-fourth inch pivot pin. If the sear will not slide back and forth freely, file and polish it until it does. Drill another one-fourth inch hole from the front end, centering it between the sides, one-fourth inch from the bottom. This one should be c1ose to one-fourth irch deep. Construct a coil spring and follower as shown, and insert them in the hole. After the pivot pin is installed, the spring should have enough compression to hold the sear firmly to the rear.

Then, when the fire selector is set on semi-automatic, the trigger nose will be in the forward position. Then, when the trigger is pulled, tl'le breech block moves forward, relieving the pressure on the sear. With this pressure relieved, the compressed spring within the breech block moves it to the rear one-eighth inch, disenJaging it from the trigger before it will again engage the sear. Conversely, when in full automatic mode, the trigger nose is moved to the rear one-eighth inch, and remains in this posiliW", in constant engagement with the sear, thus permitting the breech block to continue to mcve forward without interruption until the trigger is 'eleased.

This probably sounds somewhat complicated; but after you study and understand it, you' II find that i1' s one of the simplest selective fire trigger mechanisms found anywhere. Alter the hole for the onefourth inch pivot pin is located, drilled, and tapped, these shoulders and the trigger nose should be adjusted 'JY filing, stoning, ancl polishing.

When the fire selector is turned to semi-automatic, and the trigger is in the forward position, the spring inside the sear should push 1t to the rear, thereby disengaging it. When the sear is then pushed forward, as it would be with the breech! One more one-fourth inch hole must be drilled as close to the front of the sear as possible to receive a sear opening.

This is simply another small coil spring with enough compression to hold and return the sear to its engaging position. The forward e1d of the housing should be shaped as shown to enter its receptacle in the rear of the magazine housing. Then drill a three-eighths inch hole through the bottom center of the trigger housing, one and oneeighth 1.

With the trigger housing clamped in place on the receiver, locate and drill a corresponding hole in the receiver. A three-eighths inch by twenty-four steel nut may be welded over the hole to receive the stock bolt, which will eventually hold the completed assemblies together. Left side of complete gun is pictured al right. The fire selector swotch on this gun is different hom the one shown in the drawings and descrobed "' the text.

Drill a lengthwise hole through the grip blank, one and three-fourths inch from the front edge, centered in the width ol the grip blank. The hole should be just big enough to slip over the tubing, which you welded to the trigger housing in the process mentioned above. It is important that this hole be square with the top side, so takecare to make it so. Alter the hole is drilled, slip the grip blank over the tubing and push it as far as it will go.

With it in place, the outline of any material to be removed may be marked with a pencil. Some of the wood will have to be removed from the top, to allow the grip to slip up over the sides of the trigger housing. This can be done by carefully marking the outline and by making parallel saw cuts to the required depth, as close together as possible. After which any remaining wood can be removed A four inch section of tubing, with an inside diameter that will accept a three-eighths inch bolt, should be aligned with the hole at the rear of the trigger housing.

This tubing does not have to be very strong, since it is used mainly as a spacer and to reinforce the wooden pistol grip. Any material that will weld to the trigger hotJsing may be used, including iron pipe. If these materials are not available, cut a four inch section from an old rifle barrel and drill a hole with a three-eighths inch drill. If not, it might be necessary to file the interior of the tubing until a three-eighths inch bolt enters freely. The pistol grip may be made from any close grained hardwood such as walnut, wild cherry, maple, gtJm, and others.

Pick a piece that is as straight grained as possible and try to stay away from brittle wood that will crack easily. The grip blank should measure at least 69 U,.. Tho top of the grip Should fit closely against the boltom of lhe stocK retainers. If the metal parts are given a thin coating of lipstick and pushed as- far as they w ill go i nto the wood, high spots or wood to bo removed will be easny detected tt;l'ough traces of the tipstick on the wood , Work stow..

When shaped to suit you, sand h smooth.

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Aft4lr mo Sill"d,,g fs completed, a stain or varnish may be added to suit your laney 1 suggest thai you use a waterproof finish. If you have no special prelerencc, try brushing on. With the and cap removed from the receiver, tighten the trigger housing bolt and make sure the bolt does not protrude into the receiver. If you can find a jack handle from the screw jack of standard Ford half-ton trucks, you will have an ideal piece of material to make your stock.

One from a fairly late model is required, since the older trucks came with a jack handle that folded in the middle and had shorter pieces. For the last few years,! This is the one 'OU should be looking for. A section approximately thirty-six inches long. It should be marked at the middle and bent into a "U" shape with the bottom of the "U" having a radh. It may be bent to shape freehand, but a neater job will result if it's heated to a bright red or orange color before bending to shape around a three-fourths inch to one-half inch diameter section of round stock.

About five inches up from the bottom of the "U," bend both legs downward ninety degrees. Again, a neater job will result if heat is applied first. The butt end, or the end that goes against your shoulder, should be slightly curved to fit your shoulder. Keep the legs coat is thoroughly dry, sand back the grip nearly to the surface of the wood.

Several coats of "Tru-oil" or "lin-speed" may then be added, making an extremely durable and waterproof finish. After you are satisfied with the finish and after the trigger housing 11as been polished and colored blued, painted, etc. This may be done by giving the Interior surfaces of the wood and the outside surlace of the tubing section a liberal coating of epoxy cement and by pressing the parts together, with clamps or with y Uf hands, until dry.

Any surplus cement should be wiped off both metal and wood, simply to keep the job from looking sloppy. The washer should also be cemented into the bottom o1 the grip with the same epoxy cement. This bolt should extend through the grip and thread 1nto the nut that is welded to the receiver body.

In addition to the hexagon head which a five-eighths inch wrencl1 fits, a screwdriver slot should be sawed or filej across the head of the bolt, wide enough to accept a twenty-five cent piece. This will enable you to take it apart later, even if a wrench is not available. Ck end , to accept a short length of coli spring. This w11t keep the latch engaged 1n o slot on each leg of the stock. If desired, the front sight may be adjusted for horizontal movement by sliding it in the opposite direction to the desired point of impa:: Verlical adjustmerlt may then be made by raising or lowering the rear sight.

However, since it would require a hammer and punch or similar tools to move the front sight, it would be better to make a rear sight, fully adjustable for both elevation and windage. If available, the rear sight assembly from a United States 03A4 rifle, or similar rifle, can be used. It should be fitted as close to the rear of the receiver as possible, by making a mounting bracket and brazing or screwing it in place, in the center of the top of the rear receiver.

A satisfactory front sight can be obtained by sawing the lower part of the barrel band from the front sight of an old World War I or II military rifle. File the bottom to the same radius as the receiver and fasten it in place by brazing, or with screws, or through a combination of both. In the event that these sights are not available, it will be necessary to make a set from scratch, with sheet metal as I illustrated with the other parts.

The front sight may be made from sheet metal in one of two ways; by filing or milling from a solid block, or by welding separate sections together. I personally believe that a fronl sight, filed from a solid block with an integral protective ear on each side of the sight blade, will prove to be sturdier, and therefore the most dependable. It should be fastened to the receiver with two screws and silver solder. File one side of a block of steel, three-fourths inch square, to lhe same radius as the receiver body.

This will be the bottom of the sight. Turn it over and lay out 79 M. Two will act as guide lines to mark a one-eighth inch blade in the middle of the sight body. Lay these out, one-sixteenth inch on each side of, and parallel to, the center line. The other two lilles should be made on each side, one-eighth illch inside the outside edge. Now, with a series or parallel saw cuts, finished with a file or with file cuts only, remove the metal between the blade in the middle and the outside walls to a depth of three-eighths inch.

The outside walls should be beveled or rounded toward the top, and flared slightly outward by beveling. These outer walls serve only to protect the sight blade. They should be rounded at the front and rear corners to create a better appearance and to prevent the sight from catching on clothing. The rear sight is a little more complicated. Since I feel that adjustment for both windage and elevatioll is mandatory, this is the type I will illustrate.

The rear sight shown here is quite similar to the U. It is very sturdy because the outside walls guard the sight proper. The main body may be bent to shape from one-eighth inch sheet stock. Another piece must then be used on the bottom as a fillet between the bottom of the sight and the curved surface of the receiver. If this method is used, cut a strip seven-eighths inch wide by three inches long, and bend it around a threefourths inch wide block of steel to form a square "U" shaped box.

The sides should oe shaped as shown in the drawing. The bottom fillet must be cut to approximately the same shape as the bottom of this sight body and filed to the radius of the receiver body. This will be "sandwiched" between the sight and receiver to make a close fitting installation. Another method, probably better in the long run, would be to make a bottom section from one-fourth inch thick stock, three-fourths inch wide and seven-eigh: The bottom radius should fit the receiver and an outside wall of one-eighth inch sheet, that should be welded or brazed to each side of the bottom section.

After the rear sight is properly shaped, through either method, a. The windage adjLstment screw goes in this hole. It may be formed completely with tiles. However, a small, flat pillar tile is necessary to cut the slot in each side. Be careful not to get the saw blade hot enough to affect its heat treatment while grinding it narrow. The rear sight itself is made by bending a threeeighths in: The sight aperture may be drilled with whatever size drill you desire. I recommend a oneeighth inch aperture.

The flange on each side of the sight should closely fit the slots in the sight body. Also, a keeper, or retainer, made from flat spring stock, should be fastened to the top of the sight with a screw. I have purposely avoided mentioning any click values, wherein one click or partial turn of the windage knob or fore and aft movement of the elevation slide would equal so much at a given range.

There are too many variables to consider to make this practical.

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The distance between the front and rear sight, the number of threads per inch on the windage screw, and the angle of the elevation slide would all have to be exact to accurately predict this. Therefore, you must practice shooting your gun, moving the sights until they are in line with the same point that the bullet strikes, at whatever range you choose.

Drill a corresponding hole through the sight block crosswise to receive the windage screw. This hole should be drilled with a Number 29 drill and tapped with an eight by forty, or whatever thread pitch fits your screw. Drill another hole from the bottom side in tt: This serves to keep looseness or play to a minimum between the block and sight body. A Number 8 steel screw, one and one-fourth inch long, is used as a windage screw. Turn the head down until only a small flange remains.

This flange should be countersunk slightly into the sight body. Make a knob to screw on the projecting end of the screw with a lock screw to secure it to the windage screw. The outer rim of this knob should be knurled if possible. Various dealers, in surplus and junk, advertise these parts in many of the gun magazines and trade papers, such as Shotgun News. One of the best buys on the current market is the Sten Gun Clip. Presently available for around four dollars, these clips are truly a bargain for anyone having any use for such a magazine.

They hold thirty-two rounds of nine millimeter ammunition and the entire upper portion, including the lips which hold the cartridges in place, is reinforced with an extra thickness of sheet steel on the back and sides. This results in a strong, virtually i11destructible magazine. Assuming these are still available when you need one, I recommend that you buy at least one extra, and more if your budget permits. If there comes a time when these are no longer available, an alternate source must be found. This means making yoc1r own, which at first glance may seem almost impossible.

However, a closer look will reveal that perhaps it isn't so difficult after all-only time consuming. If a clip needs to be made to approximately lhe dimensions and capacity of the Sten, then a piece of nineteen or eighteen gauge sheet steel, five inches wide by ten inches long will be needed. The eighteen gauge material is. If the double thickness is used in the upper portion, an additional section three inches by three and one-half inches would be required as well as a one and onefourth inc! In addition, all four corners should be slightly rounded.

Place the male portion of the die inside the female portion, with a shim of sheet metal on each side. This shim should be of the same thickness as the magazine material to keep it centered. Then drill a three-eighths inch hole at each end, close enough to each end so that t1ere is room for the ten inch magazine to be formed tetweer them.

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The holes should be drilled through toth the male and female dies simultaneously while they are together. A close fitting guide pin should be used in each of these holes, to keep the die in line while the magazine is being formed. If the dies are to be used more than once, a slightly oversize pin should be pressed into each end of the female die and the holes in the male die should be reamed to a close slip fit over them.

If you only plan to use the dies a few times though, loose pins will suffice. After greasing lightly, center the sheet metal blank across the top of the female die. The male die also lubricated lightly should be centered on top of the sheet netal blank, and then the whole business should be squeezed together either in a press or with a large vise. A female forming die should be made with a "U" shaped cross section formed by bolting, riveting, or welding two lengths of three-eighths inch or thicker steel to a center section of the same material which w iII be.

The sides should be one and one-half inch high, measured from the inside bottom section. The length should be at least twelve inches. Slightly bevel or chamfer the inner top wall and polish it until it is as smooth as poss,ble. If only a few magazines will be formed, angle iron may be used to make this forming die, provided that another piece is welded across each end to prevent it from spreading open. A male die must be made to fit exactly the opening in the female die, less double the thickness of the material being formed, less another.

This simply means that if the opening in the female de is. In this case, the male die would have to be. There should also be. The jack will force the die together, forming the sheet metal into the shape of the magazine. Either method will form the front and both sides of the magazine body. Then the back side must be formed. After placing a bar of steel along the side of the sheet metal, still extending from the top of the die, tap it smartly, bending it toward the middle. Do this on both sides. This rod should be brazed, soldered, riveted, or otherwise fastened to the plate.

To complete the outside form, place the plate,' will": When the bond is secure, remove the form from the die by pushing the male die out from one end. The seam should be sweated solder , brazetl, or riveted together, atter which the lips should be cut to shape and bent inward to the shape shown. The reinfo-cing section is made in the same manner except it only has t1ree sides with the front left open. When formed to the proper shape, witt: The bottom sides must be flared at right angles outward from the magazine body, leaving a one-sixteenth inch lip projecting from each side.

The bottom plate will slide onto these lips. This can be done with a hammer and a flat bar of steel, but the male die should be placed back inside the magazine while forming, to prevmt it fr m being bent out of shape. Clamp a flat plate to the side, flush with the bottom of the angle. While holding the flat bar against the bottom, make the bend by tapping it with a hammer. The bottom plate is made to the dimensions shown it shoulci just slip over the bottom of the magazine by bending to shape in the same manner or by forming it in the small die. After it is shaped, drill a threesixteenths inch hole somewhere close to the center and make a matching keeper by drilling through a plate which is sized to fit inside the bottom of the magazine body.

Then rivet a three-sixteenths inch diameter projection in place. The purpose of the bottom of the magazine spring is to bear against this keeper, pressing it firmly against the bottom plate with the stud engaging the hole. This will prevent the bottom plate from being removed unless the stud is pushed inward. The magazine follower may be made from one-half inch Hat stock. By filing and grinding a proper bevel as 95 SUM llR! Also, drill a one-sixteenth inch hole near one end.

Then, with one end of a length of one-sixteenth inch music wire or spring stock fastened in the hole, feed the remainder through a groove filed in a one-half inch square bar some ten inches long. A useable spring will result if the bar is wound around and around the mandrel. I said a useable spring. It may not be particularly pretty. Somewhere between five and six feet of wire will be required to wind such a sr;ring. If music wire or spring stock is not available, a screen door return spring or similar spring will have to be straightened out and reworked.

This will not be easy, but it can be done, if nothing else is useable. This requires rather complicated, complex shaped dies though. So, unless a large number of magazines are to be made, I recommend the welced-up follower. Start by grindirg the front and back edges unt i I they are round. Then thread the barrel into the receiver until the breech end is flush with the inside front wall of the receiver.

With this accomplished, the lock nut should be tightened firmly against the front face of the receiver, locking the barrel in place. The finng pin should be removed from the breech block simply as a safety precaution. This being done, slip the breech block into the rear of the receiver, insert the cccking lever and the cocking lever retainer in the rear of the breech block, and attach the action spring.

Following these steps, screw the breech plug into the rear of the receiver. To assemble the trigger group, insert the trigger, with ils return spring in place, into the trigger housing.

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Then, with the trigger held forward as far as possible, slip the fire selector switch through the hole and fasten it in pace with the threaded pin. By row, all the parts and components of your gun should be completed. The working parts should all have a smooth finish, free from burns and scratches. The flat parts, such as the trigger and sear, should have flat smooth sides, square with the top and bottom and finished until thev feel slick when handled.

A good way to accomplish such a finish is to place a sheet of abrasive cloth on top of a piece of plate glass, and firmly rub the part to be polished back and forth across the mounted abrasive cloth. An extremely fine finish may beobtained in this manner. With all interior oarts finished to your satisfactior, begin assembly of the gun by screwing the five-eighths 99 the action slowly by hand. If the magazine housing has been left a little longer tl1an the finished depth requires, the bullet nose will strike the front wall of the receiver instead of entering the chamber.

This being the case, note about how much you think it lacks and carefuiiV file a little off the bottom of the magazine housing and try it again. Keep filing and trying, a little at a time, until the butt, when allowed to move forward, strips the top cartridge from the magazine and feeds it into the chamber in the end of the barrel. The sear may now be installed in the trigger housing. You should be pressing in while starting the threaded sear axis pin from the side. After the end of the axis pin slips past the spring and follower, continue pLshing in on the pin while s owly withdrawing the punch or screwdriver until the end of the pin contacts the threaded hole in the opposite side of the trigger housing.

The pin is then screwed tightly info place. Now insert tl1e stock latch, with its spring, and pin it in position. The woocen pistol grip should be in place, but not yet cemented I hope! Cementing is done after the bluing. The trree-eighths inch bolt is then inserted in the hole through the bottom and tightened, drawing the trigger housing snug against the bottom of the receiver. Then slide the magazine, with one or more dummy rounds of ammunition enclosed, into place in the magazir"le housing as deep as it 'Nill go. Secure them by wrapping with tape or wire or even heavy string.

Cycle Go slow with this since it is easy to take off too much metal. If too much is taken off, the bullet nose will hit the barrel or receiver wall above the chamber and refuse to enter. When and if this happens, about the only thing you can do to salvage the job is to weld a strip of metal along 1he bottom of the magazine housing and start the fitting all over again. If you manufactured your own magazine, wait until now to cut the notch to engage the latch. With the magazine properly fitted, use some sort of spotting compound such as Prussian blue or lipstick on the face of the latch to imprint its -,.

If the breech block did not remain open, a little more fitting will be necessary. The sear should catch the breech block in its rearward position. If it does not, you may not have the trigger mechanism made or fi1ted properly. If the trigger mechanism is working properly, which is probably the case, then either the breech block is too heavy or the sprinQ is too strong.

In either case, the breech block would not be able to travel far enough to tt'e rear for the sear to catch it. Try cutting one coil off the recoil spring and then try another test-fire, again using only one round. If the breech block does not remain open after firing, cut off another coil and try it again.

Repeat a third time if necessary. If it still doesn't work after cutting off a third coi I, something else must be wrong, or else you had one hell of a stiff recoil spring to begin with. Try polishing the breech block and the inside of the receiver body to reduce friction. If it still doesn't work properly, turn the breech block to a smaller diameter only one-sixteenth inch or so , leaving a full diameter band, approximately one-fourth inch wide at each end.

Be careful not to weaken the spring or lighten the contact point on the back of the magazine. Then cut the notch to fit. Shake out the powder, fill it with oil, and let it soak for a day or two, to inactivate the primer. Do not let a firing pin hit these primers even then. Keep the firing pin out ol the breech block until you are ready to test-fire ;he gun. If you are satisfied with the way the gun feeds by hand cycling, you are now ready to test-fire the gun. Reinstall the firing pin in the breech block and tighten tt'e lock screw securely against it.

After re-assembly, place the fire selector on semi-au1omatic and load a round that's one, a single round I in the magazine. If everything works the way it should, the round will be stripped from the magazine and fired by the forward moving:: After firing, the breech block should have traveled rearward far enough for the sear to catch and hold it in tt'e rearward or cocked position.

If it did, congratulations! Now try it with twc cartridges, still as a semi-automatic. We will get the full automatic functioning soon, but some of the parts To check against this happening, wrap a layer of tape around tl'1e receiver, ccvering the last onehalf inch of the cocking lever slot, before trying to fire again. When you are satisfied that you rave it adjusted and w: The trigger must be released and pulled again to fire SLbsequent shots.

Anything else IS unacceptable and. Assuming that it does work correctly, the gun should now be disassembled and the parts heat treated as described in the next chapter. This will prevent having a run-away gun if something should break or fall to work properly. It isn't my idea of fun to have a 1ull automatic with a full magazine continue to fire after you release the trigger. At that point, all you can do is hold the damn thing and hope it runs dry before you hit anybody.

So, test it thoroughly with only a few rounds in the magazine before stuffing H full! Another important part that deserves special mention is the nut that you welded to the bottom of the receiver that the trigger housing retaining bolt threads into. Matching threads should continue on through the hole above the nut. The bolt should be long enough to screw ir almost flush with the inside of the receiver.

Do not neglect this! I once saw a submachine gun receiver and barrel unit break loose from the grip and trigger mechanism while the gun was being demonstrated. The ba'rel fell to the ground and continued to fire, jumping and kicking in every direction. The four spectators and demonstrator scattered to find something tc hide behind. Luckily no one was injured or killed, but they very easily could have been.

Even though there is probably little point in doing so here, I will attempt first of all to give a brief description of what takes place during the heat treatment of carbon steel. In carbon steel that has been fully annealed, we would normally find two components apart from Impurities such as phosphorous, sulpher, and others. These components are a chemical compound, iron carbide, in a form metallurgically known as cemenllte, and the element iron in a form metallurgically known as ferrite.

Cementite is made up of 6. A certain proportion of these two components will be present as a mechanical mixture. This mixture, the amount depending on the car- bon content of the steel, consists of alternate layers or bands of ferrite and cementite. When examined under a microscope, it frequently resembles mother of pearl and, therefore, has been named pearlite. Pearlite contains some O. B5 percent carbon and A fully annealed steel containing at least 0. Such a steel is known as eutectoid steel. Steel having a carbon content above 0. When annealed carbon steel is heated above a lower critical point, a temperature in the range of to degrees Fahrenheit depending on the carbon content, the alternate layers or bands of ferrite and cemen more below the slow cooling transformation temperature of approximately degrees Fahrenheit.

As the cooli1g rate is increased, the laminations of the pearlite, formed by the transformation of the austenite. As the cooling rate is further increased, this transformation suddenly drops to around degrees Fahrenheit or lower, depending upon the carbon content. The cooling rate of this sudden drop in transformation temperature is referred to as the critical cooling rate.

Wt'en a piece of carbon steel is cooled at this rate or faster, a new structure is formed. The austenite is transformed into martensite which is characterized by an angular needlelike structure and an extreme hardness. If the steel is subjected to a severe quench or to extremely rapid cooling, a small percentage of the austenite may remain instead of being transformed into martensite. Over a period of time, this remaining austenite will be gradually transformed into martensite even if the steel is not subjected to further heating and cooling.

This process continues until the pearlite is thoroughly dissolved. If the temperature of the steel continues to rise, any excess ferrite or cementite present in addition to the pearlite will begin to dissolve into the austentite until only austenite is present. The temperature at which the excess ferrite or cementite is completely dissolved in the austenite is called the upper critical point. This temperature has a far wider range, depending on the carbon content, than the lower critical point. If the carbon steel, which has been heated to a point where it consists entirely of austenite, is cooled slowly, the transformation process which took place during the heating will be reversed.

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The upper and lower critical points will occu' at somewhat lower temperatures than they did during the heating. Assuming the steel was originally fully annealed, its structure upon returning to atmospheric temperature after slow cooling will be the same. By structure I'm referring to the proportions cf ferrite or cementite and pearlite: However, as the steel's cooling rate from an austenetic state is i'lcreased, the temperature at which the austenite begins to change into pearlite drops more and often results in an appreciable increase in volume and the setting up of new internal stresses in the steel.

The process of hardening steel consists fundamentally of two steps. The second step is to quench the steel at a rate faster than the critical rate to produce a martensitic structure. The critical or transformation point at which pearlite is heated into austenite is also called the decalescence point. If the temperature of the steel was observed as it passed through the decalescence point, you would notice that the steel continues to absorb heal without appreciably rising in temperature, although the immediate surroundings become hotter than the steel.

When this point is reached, the steel will give off heat so that its temperature will momentarily increase instead of continuing to fall. The recalescence point is lower than the decalesceroe point by anywhere from eighty to degrees Fahrenheit. The lower of these points does not manifest itself unless the higher one has first been complete- ly passed. These critical points have a direct relation to the hardening of steel.

Unless a temperature sufficient to reach the decalescence point is obtained, so that the pearlite is changed into austenite, no hardening action can take place. And unless the steel is cooled suddenly before it reaches the recalescence point, thus preventing the changing back again from austenite to pearlite, no hardening can take place. It is this variation in critical points that makes it necessary to heat different steels to different temperatures when hardening. After the hardening process, most, it not all, steel parts will require tempering or drawing.

The tempering process consists of heating the hardened steel to a certain temperature and then cooling. With the steel in a fully hardened state, its structure is made up mostly of martensite. However, when it is reheated to a temperature of about to degrees Fahrenheit, a tougher and softer structure known as troosite is formed. If the hardened steel is 1nstead reheated to a temperature between and degrees Fahrenheit, a structure known as sorbite is formed.

This has some power and a fan for a blower. A pyrometer is also necessary to measure and regulate the temperature. It is also possible to harden and temper parts by using the flame of an oxy-acetylene torch, a forge, or by hot bath. The latter method may be either a chemical solution or molten metal. This method is especially well suited to irregularly shaped parts, parts with holes, and parts varying in thickness or mass.

All tt'ese parts will heat uniformly to the desired temperature in a bath. There are times, however. While this method may be far from foolproof, satisfactory results may be obtained if sufficient care is taken. In many cases you will not know the exact composition of your steel, so a bit of experimenting with a scrap of the same material is in order before beginning.

Since most of the medium and high carbon steels must be heated to between and degrees Fahrenheit for hardening, try heating the scrap to a bright, clear, glowing red, devoid of any yellowish tinge. This is the "cherry-red" so often mentioned in connection with heat treating activities. Then promptly plunge it into a quenching bath of water, at approximately seventy-five degrees Fahrenheit, or a bath consisting of SAE 10 motor oil.

It shotJid now be so hard a file won't what less strength than troosite, but it also has considerably greater ductioility. Actually, all this bolls down to simply this; many of the parts that you have made or will make will require hardening. In certain instances this is required only to prevent undue wear, and in others, both to inaease strength and to prevent battering or other malformation. So it will be necessary for you to heat the part to be hardened to a temperature above the upper critical stage forming austenite , then rapidly cool it by pumping it into a quenching bath which may be oil, water, brine, etc.

The hardened steel is then heated once more to a temperature somewhat between and degrees Fahrenheit and cooled forming either troosite or soroite. The exact temperature required for this tempering or drawing operation varies considerably, depending on both the carbon conter,t of the steel and the strength and hardness requirements.

A usable gas furnace may be built by simply lining a steel or iron shell with firebrick, and then by adding a vacuum cleaner motor for touch it. If it is not, try another scrap with a little hotter: Nearly all carbon steels change color in the same way and at almost the same temperatures, so the hardening and tempering colors which appear while heating will ndicate the approximate temperature of the metal. The chart at the end of the chapter gives a fairly broad color range and may be used as a guide. There is currently a product on the market called ''Temilag" that will take much of the guesswork out of the temperature control.

It is available from gunsmith supply houses, such as Browne!!

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A thin coat is applied to the surface to be heat treated. Actually, only a thin smear is required. After it drys to a dull finish, begin heating the metal. When the proper temperature 1s reached, the Temilag will melt sharply and should oe quenched immediately. Regardless of the temperature indicator used, the hardened steel must be drawn or tempered after quenching.

So, either wipe on a smear of Tempi lag or heat the metal to the color indicating the temperature desired, then allow to cool. It would be wise to again experiment with a hardened scrap of the same material before attempting to temper the actual part, and test it again after tempering with a file and a punch. Another method which may prove useful for drawing at temperatures up to degrees Fahrenheit is the use of the kitchen oven.

Simply place the parts in the oven and set to the desired temperature and let it heat for thirty minutes to an hour. This is similar to the case-hardening process, which I will not attempt to explain here, since the Kasenit process will give similar results with less equipment. It might be helpful to include a brief breakdown of the SAE numbers used in drawings and specifications to indicate a certain kind of steel. We read about , , , etc.

The first figure indicates the class to which the steel belongs. Thus, "1" indicates a carbon steel; "2"-nickel steel; "3"-nickel-chromium Hardening and Tempering Colors steel; "4"-molybdenum steel; "5"-chromium steel; "6"-chrome-'llanadium steel, etc. In the case of the a loy steels, the second figure generally irdicates the approximate percentage of the predominant alloying element. Brightly polish the part t.: It should be remembered that the methods and descriptions in this chapter apply to carbon steel only.

Certain alloy steels may require entirely different methods of heat-treatment. Aoove all, screw and pin holes must not be dished or rounded. It is indeed desirable to have power polishing equipment-but only as a timesaving measure. Power polishing will result in top quality, but only after extensive practice. By using your set of files, strips or sheets of abrasive cloth in progressively finer grits, and a couple sheets of crocus cloth for the final finish, a finish equal to, or better than, that obtained by power polishing equipment may be obtained.

Files are used to smootJ'1 the component parts, clearing up toolmarks, dents, etc. The correct grit cloth is then applied, using stips of the cloth around the curved surfaces of barrel and receiver alike. Any dents or low places will be revealed through this process. After this cross polishing, the parts should be flatpolished by wrapping strips of cloth around files or It seems that every six months one of the national gun magazines publishes an article revealing the "secrets" behind obtaining the blue or black color on finished firearms.

Unfortunately, most of these articles and many of the gunsmithing books themselves are lacking in their explanations of how a good blueblack finish is obtained. In this respect, they are actually perpetuating the ''mystery" instead of ending it. Probably one of the most mlsunders1ood notions is the most basic, what to look for in a gooc bluing job.

A shiny coloring on the metal does not necessarily indicate a lob well done. A good blue job will have an even color, all tool and abrasive marks polished out, and all corners and sharp edges still cornered and sharp. Flat surfaces should be flat, without low places. There are several types of grease-cutting compounds or detergents on the market today, available in grocery, paint and hardware stores.

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