Hie short closed holt is made in the same manner and lo I he same outside dimensions, except that instead of the fixed firing pin, a .070 inch hole is drilled in the center of the bull countcrbore. A No. 50 drill is correct for this. Before the eouiilerfaore is cut, this hole should he started with a center drill, fed by the tail stock chuck. The drill is then used to drill the small hole approximately 1/2 inch deep. The exact depth doesn't matter since a larger hole, dulled from the opposite end, will enlarge most of it. Thib small drill should be withdrawn and cleaned frequently, and amply lubricated. Otherwise it may very well seize and break off in the hole. 11 this should happen, you might as well get another piece of material and start over, since that would prove far easier than gelling the broken drill out.
I he counterbore can now be cut to its hill depth and diameter, removing any trace of the oversized hole made by the center drill.
Since the firing-pin design used in the original bolt would be hard to improve on. we will use it in our boll. A surplus military firing pin should be acquired before the holt is machined to accept it. These are plentiful at present, and at a good price. If none are available, one can be lathe turned using the dimensions and directions shown in the Small Pails chapter ( Diagram U42). The holt body is reversed in the lathe chuck and, starting the hole with a center drill, an opening to accept the firing pin is made. This opening will consist of three diameters, four if the firing pin hole nose hole already drilled is counted. Start by drilling with a I/4-tnch drill to a depth of i inches. This depth need not be exact, but close approximation should be kept, litis is followed by drilling with a 3/8-inch drill to a depth slightly less than 1.450 inches.
This portion requires a square, or flat, shoulder at the bottom. It can be formed by using a 4/8-inch end mill to reach the final depth. Ibis should be as close to the previously mentioned depth of 1.450 inches as possible. A smaller hole, .120 inch in diameter, extends from the bottom of the 1/4-inch diameter portion to a point just behind the bolt face. This should have a total depth of 4 inches. Since ordinary twist drills of sufficient length are not normally available from hardware stores and the like, arid even those obtained through special order are limber and subject to easy hreakagc, we can make up a suitable drill for this purpose fairly easily.
Chuck a piece of 1/4-inch drill rod that is at least 4 inches long (7 inches if you ever intend to make up the full length bolt described next) and, using the tail stock chuck, drill a hole in one end using a No. 31 drill. This, of course, is started with a center drill, which by now should be standard practice. The drill is then reversed and. with a small amount of flux applied, pushed into the hole just drilled and silver-soldered in place. The end of the drill protruding from the drill rod (it should protrude at least 1 inch) must be protected from the heat used to silver-solder it in place to prevent drawing the temper. It will likely be necessary to polish the larger 1/4-inch section where it was heated before it will enter the hole freely. The depth of these holes can be regulated closely through the use ol slops made by fastening close-fitting eolJais around the drill stems, or extensions, with the exact length to drill the holes extending. Such culiars can he fastened in place with solder ot epoxy.
This holt design requires two small-diameter recoil springs located on either side of the firing pin. The recoil springs tised in the military Ml carbine arc well suited for this. They are plentiful and cheap. The diameter of these is approximately .260 inch. The holes to accept these should be slightly larger fur clearance. A 17/64-inc.h drill, which measures .2656 inch, will serve well for this. Ihese holes should be 2.700 inches deep and measure .800 inch apart from center to center with .400 inch on each side of the ccnterline.
A slot must be cut. as shown in the drawing, to permit the hammer to move forward far enough to contact the firing pin. This is done by clamping the boll in a vertical position in the milling machine and culling it with a 3/8-inch end mill. I his sloe should be inch deep, provided that the overall length of 4.200 inches is adhered to. ITiis will provide a shoulder so that when the hammer is fully forward the firing pin will protrude .(ISO inch through the holt facc. Ihe dbtancc from the extreme front of the bolt nose to this shoulder should be inches.
Firing pin protrusion can be checked and verified by pushing the firing pin forward—preferably with the return spring in place—flush with the shoulder and measuring the protrusion with a depth micrometer.
At the location shown in Diagram ¿'5, a crosswise hole is drilled for ;i pin lo keep the firing pin in place. A close-fitting plug should be inserted in the firing pin hole while tins hole is drilled to provide support lor the drill. Otherwise the drill will "crccp" or "crawl" toward the unsupported side and almost certainly break.
The lull-length holt, which is to Lie used with the original recoil spring, is made in the same nanner except that in this case it will have an overall length of 6.950 inches. The rear portion, measuring 3.750 inches long, is turned to a diameter of .990 inch. This assures that it will slide, without hinding, inside the spring housing.
This time, the hammer slot must lie cut as shown in Diagram #6, with a flat shouIdeT VV2S inches to the rear of the holt's forward face, as before, and of sufficient length to allow the hammer to travel forward and hack without interference. While not actually necessary, it Is easier to rut this slot all the way through the bolt body from top to bottom than the partial depth required.
Hear view of open bolt (left) and closed b'jit irighej.
I he extractor pin holes are in the same locution on all three versions and should he drilled with the extractor clamped in place lu ensure that they line up exactly.
The cocking lever, or operating handle, is also of the same dimensions and in the same location on all three versions. The correct location for the hole in the bolt is fixed by marking its location through the receiver slot with the holt in place and in the closed position Hie operating handle must not contact the front of tin- slot. If possible, this hole should be drilled in the milling machine with a slightly undersized drill atid finished with a 3/8-inch end mill, forming a Hal bottom in the hole.
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