of your gun should be completed. Before heat-treating the parts and before beginning the final polishing and bluing, you should assemble and test the gun. Whatever additional fitting and adjustment are necessary should be done at this time.
The working parts should all have a smooth finish, free from burrs and scratches. Such flat parts as the hammer, trigger, and sear should have flat, smooth sides, square with the top and bottom and finished to a point where they feel slick when handled.
A good way to achieve 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 can be obtained in this manner.
With all of the interior parts polished to your satisfaction, begin assembly of the gun by placing the extractor in the slot provided for it in the bolt, together with the spring, and pinning it in place. If the closed-bolt version is used, insert the firing pin and spring into the bolt and pin them in place. Then place the bolt inside the receiver and install the cocking lever. Insert the barrel in the forward end of the receiver where it is held in place by screwing the combination barrel nut/barrel shroud in place. Now place the action spring and guide inside the rear end of the receiver with the forward end of the spring inside the hole in the bolt.
To assemble the trigger group, insert the lower sear, with its return spring in place in the trigger housing, and pin it in place. Install the trigger, with the trigger bar pinned to it, in place and pin it. Attach the trigger return spring to the trigger bar, with the rear end stretched slightly to exert tension and pinned in place at the rear of the trigger housing. The upper sear is then pinned in place.
Use the same procedure for the closed-bolt gun, except that you'll use only a single sear, in the same location as the lower sear. Use a hammer and hammer spring instead of the upper sear.
Install the detent and spring in the safety before placing it in its slot just ahead of the trigger.
With the trigger assembly in its location inside the lower receiver, place the upper receiver in position on top of the lower receiver and thread the hinge screw through the mating parts at the front of the receiver. Then put the grip in place and secure it with the stock bolt, or grip screw, which also holds the rear ends of the receivers together.
Next, put the magazine release and spring in place and pin them, thereby completing assembly of the gun.
The closed-bolt gun can be tested for proper feeding by using live ammunition, but the firing pin should be removed as a precaution against accidental firing. The open- bolt gun will require some dummy cartridges since the firing pin is fixed in place.
Dummy cartridges are easily made, simply by seating a bullet in an unprimed case. Preferably, you should use a new case or, at least, a case that is resized to factory dimensions. The bullet should be seated to the same depth as a factory-loaded round. Make up several of these in advance.
With some of these dummy rounds inserted in the magazine, insert the magazine in the gun and cycle the action by hand. If the 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 on the bottom, the forward portion of the magazine lips should be sprung open slightly. This will raise the bullet nose in relation to the magazine body. If the bullet nose rides too high and hits the top of the barrel, or the cartridge stands straight up (stovepipes), then the magazine lips should be sprung inward, a little at a time, until the condition is corrected. Keep in mind 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 quite as much adjustment to the magazine lips as slow hand-feeding may indicate.
When you are satisfied with the way the gun feeds by hand cycling, you are ready to test-fire the gun. Replace the firing pin if using the closed-bolt version. One round of live ammunition (that's one, a single round) should be loaded into the magazine. Then, after cocking the action and while holding the gun well away from your face and body, pull the trigger.
If everything works the way it should, the round will be stripped from the magazine and fired by the forward moving bolt when the trigger is depressed (open bolt). After firing, the breech block should have traveled rearward, ejecting the empty case in the process, far enough for the sear to catch and hold it in the rearward, or cocked, position. In the closed-bolt version, the hammer should fall when the trigger is pulled, firing the round; the bolt should travel to the rear, ejecting the empty case, and return to its closed position.
If it did, congratulations! Now try it with two cartridges, still as a semiautomatic. We will get to the full-automatic functioning soon. But some of the parts should be hardened first to prevent them from being battered or worn out of shape.
If the bolt did not remain open, a little more fitting may be necessary. Try working the action by hand with the trigger depressed just far enough to release the bolt. As the bolt is pulled to the rear, the sear should catch it and hold it open. If it doesn't, you may not have the trigger mechanism made, or fitted, properly. Check it carefully.
If the trigger mechanism is working properly, which it probably is, then either the breech block is too heavy or the recoil spring is too stiff. In either case, the bolt would not travel to the rear far enough for the sear to catch it. Try cutting one coil off the recoil spring and test-fire it again, using only one round as before. If it still doesn't stay open, cut off another coil and try again. Repeat a third time if necessary.
If it still doesn't stay open after cutting off a third coil, something else must be wrong, or you had an extremely stiff recoil spring to begin with. Try polishing the breech block and the inside of the receiver to reduce friction. If it still doesn't work properly, turn the breech block to a slightly smaller diameter (only 1/16 inch or so), leaving a full diameter band, 1/4 to 1/2 inch wide at each end and in the middle.
Take care not to weaken the spring or lighten the breech block so much that it will recoil far enough to the rear for the cocking lever to strike the rear of its slot. To check for this happening, wrap a layer of tape around the receiver, covering the last half inch of the cocking lever slot. Then fire the gun. If the cocking lever does not tear the tape completely through to the end of the slot, it should 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 it 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 corrccted.
Assuming it does work correctly, the gun should now be disassembled and the parts heat-treated as described in the next chapter. After finishing the parts, assemble the gun once again and test it thoroughly both on semiautomatic and full-automatic fire.
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 with a full magazine continue to fire after the trigger is released. At that point, all you can do is hold on to it and hope it runs dry before you hurt anybody. So, test it thoroughly, with only a few rounds in the magazine, before stuffing it full.
Another important point that deserves special mention is the block you welded to the bottom of the receiver for the grip and trigger housing bolt to screw into. Matching threads should continue through the receiver body. The bolt should be long enough to screw in almost flush with the inside of the receiver. Do not neglect this! I once saw a submachine gun upper receiver assembly break loose from the grip and trigger mechanism while the gun was being demonstrated. The receiver and barrel assembly fell to the ground and continued to fire, jumping and kicking in every direction, while the four spectators and the demonstrator scattered to find something to hide behind. Luckily, no one was injured or killed, but they could have been.
The gun described in this book would separate from its ammunition supply if it broke apart as described above. The gun described in Vol. I would have continued to fire since the upper receiver would have remained intact wi rh the magazine housing. The above example does not apply to this gun, but it is included as a point of safety.
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