By now, all the parts and components of your gun should be completed. However, before the parts are heat treated and before beginning the final polishing and bluing, the gun should be assembled and teisted. Whatever additional fitting and adjustment necessary for proper functioning should be done at this time.
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 they 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 be obtained in this manner.
With all interior parts finished to your satisfaction, begin assembly of the gun by screwing the five-eighths inch N.F. lock nut onto the barrel shank. 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 firing 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 cocking 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 its return spring in place, into the trigger housing. Then, with the trigger held forward as far as possible, slip the fire selector switch through the hole and fasten it in place with the threaded pin. .
The sear may now be installed in the trigger housing. A small punch or screwdriver may be used to depress the longitudinal spring and follower inside the sear by inserting same in the hole in the front of the sear body. 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 pushing in on the pin while slowly 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 into place.
Now insert the stock latch, with its spring, and pin it in position.
The trigger housing may then be fastened in place by inserting the front end in its seat at the rear of the magazine housing. The wooden pistol grip should be in place, but not yet cemented I hope! (Cementing is done after the bluing.) The washer should also be in place, in the bottom. The three-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 magazine housing as deep as it will go. Secure them by wrapping with tape or wire or even heavy string. Cycle the action slowly by hand. If the magazine housing has been left a little longer than 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 carefully 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.
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 the bottom of the magazine housing and start the fitting all over again.
When the magazine is fitted to where cartridges feed properly with the action worked by hand,and when the bolt snaps forward after pulling the trigger, you should pin the magazine latch in place. 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
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contact point on the back of the magazine. Then cut the notch to fit.
Dummy cartridges can be easily made by drilling a small, one-eighth inch hole through the side of the cartridge case. 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 of the breech block until you are ready to test-fire the 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 the lock screw securely against it. After re-assembly, place the fire selector on semi-automatic and load a round (that's one, a single round) in the magazine. Cock the action and while holding the damn thing well away from your face and body, touch her off!
If everything works the way it should, the round will be stripped from the magazine and fired by the forward moving breech block when the trigger is depressed. After firing, the breech block should have traveled rearward far enough for the sear to catch and hold it in the rearward or cocked position.
If it did, congratulations! Now try it with two cartridges, still as a semi-automatic. We will get 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 breech block did not remain open, a little more fitting will be necessary. Try working the action by hand with the trigger depressed, or held back. The sear should catch the breech block in its rearward position. If it does not, you may not have the trigger mechanism made or-fitted properly. Check it carefully.
If the trigger mechanism is working properly, which is probably the case, then either the breech block is too heavy or the spring is too strong. In either case, the breech block would not be able to travel far enough to the 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 coil, 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
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breech block too much, or it might recoil far enough to the rear, allowing the cocking lever to hit against the end of its slot. To check against this happening, wrap a layer of tape around the receiver, covering the last one-half inch of the cocking lever slot, before trying to fire again. If the cocking lever does not tear the tape completely 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 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 finishing the parts, assemble the gun once again and test it thoroughly, both on semi-automatic fire and then on full automatic.
When test-firing as a full automatic, start by loading only two or three rounds in the magazine. This will
prevent having a run-away 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 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 it 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 in 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 barrel fell to the ground and continued to fire, jumping and kicking in every direction. The four spectators and demonstrator scattered to find something to hide behind. Luckily no one was injured or killed, but they very easily could have been. So, take care!
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