AR Sponsor
Posted: 8/15/2010 6:12:34 AM EDT
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First off - thanks for all the good info on AR 9mm build! Definitely pointed me in the right direction on several details
My nagging question is this: With a bottom loading RRA Mag Block, it has the tension screw that presses on the lower. I have seen references of the tension causing the AR lower to crack. Not a good thing on a SBR registered lower!! However, I have not been able to find a torque setting to properly tension the mag block mechanism in the mag well. I intend to put a small drop of medium strength loctite on tensioning screw and then torque it into place until my long Allen wrench begins to flex/bow a bit. Also haven't seen any pics posted of said cracked lowers. Just references to LE armorers cranking them so tight they break lowers and individuals stating it has happened to them. Just looking for first hand experience and advise. Will post pics of my build soon - all the bits and forms should be coming together in the next week or so. Wahoo!! |
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You don't need to torque the thing THAT hard. Just enough to keep it from moving. If you use a standard 4" long 1/8" Allen wrench, you should be able to get it more than tight enough by hand, but not so tight that you'll put undue pressure anywhere in the lower.
I switch mine out between my factory RRA 9mm carbine and my SBR, and I've never had it move once I tightened the tension screw by hand. |
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I don't have any torgue info.
My RRA block was loose in my RRA lower. No amount of tightening the tension screw would work for more than a few magazines. I even tried loctite (penetrating loctite as well as regular blue). I never could get it straightened out, so eventually I just drilled and pinned the block to the lower, Colt-style. It was also a registered SBR. I'm very happy I went that route, not a single problem since then. I have another SBR in 5.56, so dedicating this one to 9mm wasn't a concern. I noticed my RRA block was a lot looser than Colt mag blocks. Those I had to tap into the mag well with a rubber mallet. I think with a tighter mag well or slightly larger mag block, the tension screw would work fine. Good luck! |
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Thanks for the first hand info - wanted to hear from folks who have been running drop-in mag blocks for some time.
I was reading over the weekend about 9mm AR's and ran across a few references to cracked lowers. Got me to worrying about my lower as I just got the SBR Form 1 on it. If it was just the lower, not that big of a deal. But doing the NFA dance for another couple of months if it might crack, bigger deal. Mine seems to be a good fit between mag well and mag block so far. Using Metalform mags it has functioned great with 115gr WWB, 147gr Winchester Subs & 147gr GA Arms Subs. Should be able to get to the range this week to see how consistent it is with suppressor in place. |
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