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Posted: 6/20/2012 8:23:37 AM EDT
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Am in the process of building a 6.5 Grendel upper but ran into a problem. I’m using a ‘slickside’ DPMS upper which will not mate to my M&P lower. The rear take down pin did not lineup freely and when I did get it locked in the charging handle now sits too low and won’t clear the buffer tube collar (I’m guessing that’s what it’s called) I thought I was being clever by trying to have two uppers to use on a single lower. Any advice or does that upper receiver need a specific brand lower, i.e. DPMS?
I'm also having issues with getting the A2 Flash Hider to index properly. The provided crush washer does not crush, I actually broke my bench vise trying. Since no makes a peel washer for 9/16, would 5/8 shims made for a .308 work? As you might guess I'm kind of new to this. Thanks. |
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Quoted:
Am in the process of building a 6.5 Grendel upper but ran into a problem. I’m using a ‘slickside’ DPMS upper which will not mate to my M&P lower. The rear take down pin did not lineup freely and when I did get it locked in the charging handle now sits too low and won’t clear the buffer tube collar (I’m guessing that’s what it’s called) I thought I was being clever by trying to have two uppers to use on a single lower. Any advice or does that upper receiver need a specific brand lower, i.e. DPMS? Sounds like that DPMS upper is out of spec. I'm also having issues with getting the A2 Flash Hider to index properly. The provided crush washer does not crush, I actually broke my bench vise trying. Since no makes a peel washer for 9/16, would 5/8 shims made for a .308 work? As you might guess I'm kind of new to this. Sometimes you'll run across a crush washer that has more temper than it should and doesn't like to crush normally. Try another crush washer....not sure if a normal 1/2" will fit the 9/16" threads. A 5/8" will probably be a little big. If you have a 1/2" fine threaded nut and bolt, along with two flat washers and your repaired vice, I know you can flatten that crush washer a bit if you put your man hands to it. Hint: use a long handled wrench. Be sure to restrain your barrel and not your receiver when working on muzzle devices. |
A friend of mine bought an M&P 22 AR pistol. The M&P upper would not fit on an AR lower 
I would bet that the M&P was not made to be compatible with other parts. I'm not sure, but if I had to guess. Crush washers are cheap. I would search for a new crush washer and give it a try. |
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