The barrel can be turned from a commercial blank or made from a surplus military barrel. M2 barrels are presently available from Oyster Bay Industries (31 South Street, Oyster Bay, NY 11771). These are new barrels, and their biggest drawback is that they have enough Cosmoline on each one to protect a tank. On the other hand, they contain enough surplus material to allow making up most of the other barrel parts.
Included in the barrel assembly are the barrel proper, barrel extension, barrel support sleeve, muzzle brake, and barrel-retaining nut.
The M2 barrel is sawed into sections large enough to make the designated parts. The barrel sections, as well as all other parts, are squared on the ends and turned to size. All threads are 12 threads per inch (TPI).
Both the barrel section, which contacts the barrel retainer, and the retainer are turned with a matching 4-degree taper. This causes a solid, in-line lock-up and support for the barrel at the breech end. The barrel extension must have three locking lugs (which mate with the bolt lugs) machined into it. This is best done with some sort of dividing head. But if none is available, don't give up. Wrap a length of masking tape around the diameter of the part, measuring the length precisely. This is then divided into three parts and rewrapped, and their positions are marked on the barrel extension. These marks are then used as centerlines to cut the lugs with the milling machine. Some file work may be required in the shaping of these. If care is taken, a precise fit will result.
When smaller lathes are used for this, it will be necessary to turn the barrel one-half length at a time (assuming that a large enough hole to accept the smaller portion exists). If the end with the smaller diameter is pushed through the headstock, the larger end can be turned to size and threaded. Do not attempt to chamber the barrel until the barrel extension and bolt are made. The barrel is then reversed in the spindle and the smaller portion turned. The threads for the muzzle brake and barrel-retaining nut are cut at this time.
The military surplus barrels from Oyster Bay are heat-treated to a hardness that is slower and harder to machine than that of commercial barrels. However the barrels are tougher and will usually wear better arfd last longer than their commercial counterparts.
Muzzle end of barrel showing muzzle brake threads.
LENGTH AS DESIRED FROM BARREL NUT TO MUZZLE '
BARREL, FORWARD END
The barrel-retaining sleeve is made from 4140 or 4340 material. This should be a slip fit inside the receiver tube. The inside of this part (sleeve) should be closely fitted by tapering to the same dimensions as the barrel shank (I used 4 degrees) so that when pulled into place inside the receiver, and with the barrel nut tight and under a slight amount of tension, a solid installation results. In many cases this enhances accuracy.
The muzzle can now be crowned and the threads cut for the muzzle brake installation and the barrel nut. Both are cut 12 TPI.
The barrel extension, which contains the locking lugs that mate with the bolt lugs, is made from a close-fitting section of good-quality steel, preferably 4140 or 4340. A 1-inch hole is bored through the center of the part. The hole is then enlarged to 1 1 / 2 inches (1.500 inches) inside diameter by 1 3/4 inches (1.750 inches) in depth. The shoulder remaining at the bottom of this enlargement should be smooth and square since the bolt lugs lock against this. The front end is now threaded to fit on the barrel tenon. This is 12 TP! pitch by 11 / 2 inches diameter by 11 / 4 inches (1.250 inches) deep. This thread joint should fit snugly, with some effort required to screw it home.
The barrel should once again be placed in the lathe and the chamber cut. I recommend that a roughing reamer be used first, followed by the finish reamer. Accurate headspace gauges should also be obtained and used because there is sometimes quite a bit of difference between cartridges obtained from different sources. Clymer Manufacturing Company is an excellent source for these gauges.
It should be emphasized here that ammunition obtained from different sources would not even fit into a standard chamber. U.S. military and Israeli ammunitions are fairly consistent, but those from some other countries may not even allow the bolt to close. Ammunition must be made to fit a standard chamber, not vice versa.
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