Does anyone know the proper tap size for a Bushmaster grip? From what I can tell (eyeballing it) the threads are cross threaded about a 1/4" in on the lower. I can attach my grip but only get about a 1/4 of an inch of the screw in and have to use about 6 washers to accomplish this. Just wondered if anyone knew what size tap I would need to try and clean these up. I have a 5/16 tap, which is too small and a 1/4 which I am afraid is too big? Please advise. Thanks

the screw is 1/4 x 28, hope that helps

I have a 5/16 tap, which is too small and a 1/4 which I am afraid is too big?

?

he definately has it backwards

Well I ran the 1/4 tap with some anti-seize on it to ensure it went smooth and it went through. There was obviously some cross threading involved as it cleaned up the threads. However when I went back to run the grip screw in I got the same result, only about a 1/4 of an inch would go in, leaving a 2/8" gap when you would pull down on the pistol grip. I think I need to get a new pistol grip screw and see if for some reason that is the issue. The screw that I have came with the Tango Down Battle grip I bought, I would figure this would be a standard grip screw, but maybe not?? Am I missing something here?

"he definately has it backwards" Not an expert or a gunsmith by any stretch of the word, but I only know what I experienced. The 5/16th tap would go in the hole, but was way too loose, had a lot of play, etc.... The 1/4 fit much better and cleaned out the threads nicely.

now that you said TDI battle grip screw i had the same thing happen over and over, it was weird, I just had to keep taking it out and reinserting until finally after about 30 tries it went in halfway smoothly, Idon't know if it is that blue loctite like crap on there or what but something is definitly going on with the TDI screw.  I remember i had to torque the living hell out of it and I told myself to remember not to change the grip because I know I screwed up the threads in my lower

Quoted: now that you said TDI battle grip screw i had the same thing happen over and over, it was weird, I just had to keep taking it out and reinserting until finally after about 30 tries it went in halfway smoothly, Idon't know if it is that blue loctite like crap on there or what but something is definitly going on with the TDI screw.  I remember i had to torque the living hell out of it and I told myself to remember not to change the grip because I know I screwed up the threads in my lower

+1, I had problem with the TD screws as well.

Well then maybe I am going to get a new screw and try that route, yeah that is what I am going to do.

The correct thread in the lower is SUPPOSED to be 1/4" X 28, as 1Gunner mentioned.  Whenever a screw seems to start, then stop pretty fast, it may be that the screw is incorrect.  This happens often when a metric (6mm) screw is used by mistake, or perhaps a 1/4" x 20 is used.

Get a 1/4" X 28 tap and clean out the hole, and ensure you have a true 1/4 X 28 screw.  Most hardware store screws are 1/4 X 20 which aren't correct.  Go for a socket head cap screw instead, which are readily available in the finer pitch.

If the hole is completely buggered, you can drill it out for a 5/16"... use the correct drill for a 5/16" tap, then go ahead and use the tap.  You will probably have to open up your grip hole a bit.

Check the screw.  BM doesn't often do shoddy work, and I suspect the grip threaded hole is done via CNC and/or a tapping head, neither of which is known for a buggered thread.

Good luck!

edited:  Sorry a lot of this post doesn't apply to you as you have already cleaned up the hole, but I'll toss it out as general advise for others!