Assembly and Adjustment

With all the component parts completed, the gun should be assembled and tested before final polishing and bluing is done. Any final fitting and adjustment should be done at this time.

All working parts should have a smooth finish, with no burrs and scratches evident. Rat-sided parts, such as the sear and trigger, should have flat, smooth sides, square with the tops and bottoms, finished to a point where they feel slick when handled.

One way to achieve such a finish is by placing progressively finer sheets of abrasive cloth or paper on top of a piece of plate glass. (The glass provides a stiff, solid, smooth backing for the cloth.) The part to be polished is moved back and forth across the abrasive surface while maintaining downward pressure. An extremely fine, even finish can be obtained in this fashion.

When all of the interior parts are polished to your satisfaction, start assembly of the gun by installing both extractors, together with their springs, in the slots provided for them in the bolt and pinning them in place. If the closed-bolt version is used, the firing pin and striker are installed on the bolt. The barrel is inserted from the rear end and, with the indexing pin in alignment, pushed into place and secured by the barrel nut. The bolt is now inserted into the receiver and the cocking lever installed. With both the recoil spring and the striker spring in place, the recoil spring guide is installed, followed by the breech plug, which is held in place by the retaining pin.

The trigger group is assembled by first inserting the trigger block, with its return spring in place, into the lower receiver and pinning it in place. The trigger, with its trigger bar pinned in place, is put in place and pinned, making sure that the fonvard end of the trigger bar is under the projecting block at the top of the trigger block. If the two-stage trigger is used, the wire spring should be located and secured in place at this time. The trigger return spring is attached to the trigger bar, with its rear end stretched slightly to exert tension, and pinned in place at the rear of the lower receiver. The sear is now pinned in place as shown in the drawing. If only the closed-bolt version is used, the wire spring behind the trigger can be eliminated.

The upper receiver is positioned in place on the lower and secured in place using the front mounting screw. The grip is now positioned over the rear of the lower receiver and secured with the stock bolt, or grip screw, which also holds both receivers together at the rear. The magazine release, together with its spring, is pinned in place, completing assembly of the gun.

The closed-bolt gun can be tested for proper feeding with live ammunition, but the firing pin should be removed as a precaution against accidental firing. You should also determine that the chamber is cut deep enough to assure that the bolt face cannot crush the case rim as it slams forward and detonates the priming mixture. Don't neglect this; it can be dangerous. Once, I had a gun similar to this almost completed, except the firing pin had not been installed. I was going to show a friend of mine just how slick this gun would feed. I placed five cartridges in the magazine and inserted it in the gun. When I pulled the bolt to the rear and released it to feed the first cartridge, it fired all five rounds into the wall of my shop. Subsequent investigation revealed insufficient clearance between the bolt face and the cartridge head. This allowed the bolt to crush the priming mixture, firing the gun, without any firing pin whatsoever. Not only would the feds have claimed the gun was illegal, it was also dangerous and could have resulted in serious consequences.

The fixed firing pin in the open-bolt version prevents testing for feeding, but this can be done with the closed bolt in place.

With a single round in the magazine, draw the bolt to the rear and let it move forward smartly. If the cartridge feeds satisfactorily, try it with several rounds, working the action by hand. If cartridges do not feed properly, try to determine the cause by allowing the bolt to move forward slowly and observing where the bullet nose contacts the approach cone of the barrel. If it hits at the bottom, the forward ends of the magazine lips should be sprung open slightly. This will elevate the bullet nose in relation to the magazine body. If the bullet nose contacts the top of the barrel or the cartridge stands straight up, the magazine lips should be sprung inward, a little at a time, until the condition is corrected. Be advised that when the bolt strips a cartridge from the magazine during normal firing, the bullet nose will try to move downward due to pressure being exerted against the upper rear of the cartridge case by forward movement of the bolt. So it probably won't take as much adjustment to the magazine lips as slow hand feeding may indicate.

When you are satisfied with the way the gun feeds during hand cycling, you are ready to test fire. If using the closed-bolt version, replace the firing pin assembly. One round of live ammunition should be loaded into the magazine. With the action cocked, hold the gun well away from your face and pull the trigger.

If everything works the way it should, the round will fire, causing the bolt to move to the rear, extracting and ejecting the empty case. The bolt should remain in the open position in the open-bolt version but should return forward in the closed-bolt.

If it worked the way it was supposed to, try it with two cartridges, still as a semiautomatic. We will get to the full automatic part soon, but some of the parts should be hardened first to prevent undue wear or battering.

If the bolt didn't remain open (open bolt), a little more fitting may be necessary. Try working the action by hand with the trigger depressed just far enough to release the bolt. The sear should catch and hold the bolt in its rearward position. If it does not, you may not have the trigger fitted or assembled correctly. Check it carefully.

If the trigger mechanism is working properly, then either the bolt is too heavy or the recoil spring is too stiff. In either instance, the breech block doesn't travel to the rear far enough for the sear to catch it. Try cutting one coil off the recoil spring and try it again, using one round as before. If it still doesn't remain open after firing cut off another coil and try again. Repeat a third time if necessary.

If it still doesn't work after cutting off a third coil, something else must be wrong, or else you

Volume III, The .22 Machine Pistol had an extremely stiff spring to begin with. Try polishing the bolt and the inside of the receiver body to reduce friction. If it still doesn't work properly, turn the bolt to a slightly smaller diameter (only .050 to .060 inch), leaving a full diameter band approximately 1/4 inch wide at each end and in the middle.

Take care not to weaken the spring or lighten the bolt so much that it will recoil far enough to the rear for the cocking lever to strike the end of its slot. To check against this happening, wrap a layer of tape around the receiver, covering the last 1/4 inch of the cocking lever slot, and fire the gun. If the tape isn't torn by the cocking lever all the way to the end of the slot, it can be considered satisfactory. If it does, a slightly stronger spring is needed.

When you are satisfied that you have it adjusted and working properly, try firing with two rounds in the magazine. The trigger must be released and pulled again to fire subsequent shots. Anything else is unacceptable and must be corrected.

Assuming that it does work correctly, the gun should now be disassembled and the parts heat treated, as described in the next chapter. After this is done, assemble the gun once more and test fire it thoroughly, first on semiautomatic fire, and then on full automatic.

When testing as a full automatic, start by loading only two or three rounds in the magazine. This will prevent having a runaway gun if something should break or fail to work properly. It isn't my idea of fun to have a full-automatic weapon with a full magazine continue to fire after the trigger is released. If it should, all you can do is hold onto it and hope it runs dry before you hit anybody. So test it thoroughly with only a few rounds in the magazine before stuffing it full.

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