Stripped Set Screws
Here is a post from a forum on M14s on removing frozen flash hider castle nut set screws from M14/M1A rifle by the well known riflesmith Gus Fischer. Some of it may help you!
Good Luck!
Flash Suppressor Lock Nut Screws
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AKA, "Castle" nut set screws.
A couple of posts down the forum gave me the inspiration for this post.
First and this is very important if you don't know it, is how the Lock Nut was often placed when a Flash Suppressor (FS) was put on. Common practice by the manufacturers of M14's, the Arsenals, as well as many Armorers was that that after the Set Screws were screwed down all the way, they would take the FS pliers and move the Lock Nut until it rested or even was snug against the Set Screw. If you try to take a set screw out and it is difficult to turn - STOP- because this is most likely what is going on and you will more than likely strip the allen wrench hole or the threads of the set screw trying to take it out. OK, so what do you do?
I would suggest that before you try to unscrew the set screw, take the FS pliers and try to move the Lock Nut back and forth to see where it rests against the set screw. By trying this, you will find by feel where the center of the notch of the Lock Nut (where the set screw rests in the notch) and that is the best place to remove the screw.
OK, so what if the screw still won't move or is stripped? Some people put red loctite or some kind of glue in the threads of the FS for the Set Screw. That is unnecessary and counterproductive. You don't know if you are dealing with that or not with a set screw that is difficult to turn. The threads could also be rusted and thus "freeze" the set screw in place. The quickest way to overcome either problem is to heat the tip of one leg of an old or worn out 1/16" allen wrench and stick it in the allen wrench hole. You want to get the tip of the allen wrench red hot, so you will ruin this allen wrench if it wasn't already worn out or ruined. The heat will transfer through the body of the set screw to the threads and either melt the glue or loctite or free up rusted threads. Then you can get the set screw out with a good Allen wrench.
Now, what happens if the allen wrench hole is buggered up and/or enlarged so the 1/16" allen wrench won't take it out? Well, first I would still use the heat transfer method out lined in the paragraph above. Then wait about 15 minutes for the screw to cool. If you have a set of "Easy outs" and one has a small enough tip to go in the screw, that will often give you enough grip to get the screw out. Someone mentioned trying to use the square shank edge of a very small tap, and that might work, but most folks don't keep taps that small. Someone else mentioned you might be able to use a metric allen wrench that is a bit larger than 1/16". That might work. If the hole in the set screw isn't quite large enough for your smallest Easy out, or if you don't have a small easy out, you might try using just enough 5 minute epoxy to partially fill the hole and stick the long leg of a good allen wrench in it. You just want to put a tiny drop of glue into the allen wrench hole. You can use a piece of wire or a paper clip to pick up and put a small bubble of glue in the hole. Allow about 10 minutes for the glue to set up around the allen wrench and then try to turn the set screw out. Sometimes that will give you the grip you need to loosen the screw.
About a month ago, I had to get a set screw out that had almost all these things wrong with it. I finally had to drill into the allen wrench hole in the screw to open it up just a bit to get an Easy Out into it. The heat transfer method above, the vibration of the drilling, plus the shock of tapping the Easy Out into the hole - all helped to break the bond of the threads of the set screw to the FS threads and I got it out.
OK, so how do you properly tighten down the lock nut and set screw? I tap the FS back with a leather or rawhide mallet while screwing the Lock Nut back. Once it seems like the FS is all the way back, give it a sharp tap with either mallet or if you don't have either, you can use a block of wood against the FS and hit it with a regular hammer. (A sharp tap, NOT a hard whack.) Take your FS pliers and screw the lock nut on until you start feeling a little resistance, not much resistance, but just when you start to feel resistance. That means the Lock Nut is beginning to put pressure on the FS against the front of the barrel. As you look from the muzzle, look at the left side of the Lock Nut. Put one leg of the FS pliers into the notch that is closest to the top of the FS on the left side. Put the other leg of the Pliers in the opposing notch on the other side. Now WITH the legs of the plier in both notches, turn the FS pliers until the nut stops with the left side leg of the pliers resting against the top of the notch in the FS. 90 percent of the time, this will ensure the notch under the FS screw is centered up. If the screw turns hard, tighten and loosen the nut with the FS pliers again until you get the feel for the center of the notch being centered on the set screw. Then tighten the set screw down.
You aren't quite done yet. Once the set screw is down tight, pick up your FS pliers one more time. Turn the lock nut counter clockwise (or as you would be unscrewing the lock nut) until you feel the notch rest snug against the screw. Snug and not real tight. That will keep the set screw from unscrewing as the rifle is fired.
