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Posted: 4/10/2008 12:57:20 PM EDT
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Yeah I know, the subject of play between upper and lowers has been beaten to death. The concensous seems to be that accuracy isn't affected by play between receiver halves. But, I see that Rock River offers "National Match" upper and lowers that have been selected for a tight fit. (Brownell's catalogs them). Is this just marketing hype or is there some actual difference here? In one book on AR's (I don't have the name handy) that was written, I think, in the '80's, the author describes a proceedure for glass-beading the reciever halves. Anyone tried this and, if so, was there anything gained by it? Lastly, does the JP tensioning take-down pin work like a regular take-down pin or do you have to use the wrench each time you want to separate the halves? Thanks. |
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I think the national match uppers/lower combos are just for piece of mind......however. Would I enter a contest with a rifle that is so loose it makes Lindsey Lohan jealous???...HELL NO. You want the best everything if your going to win. I wouldnt say that the fit means nothing(exceptions can be made), I just think that most regular shooters wont notice shit. A professtional target shooter will see/feel things that most of us never will. Im not sure about the JP pins or the glass bedding. |
RRA's are tight enough as it is.  Hard to imagine just how tight the NM set would be. Can upper and lower slop affect accuracy? Only in the extreme. Even then, accuracy might suffer from other factors that the looseness imparts on the upper and lower. As both front and rear sights are mounted on the same plane ( upper ), accuracy should not be affected. Your follow through and subsiquent shots may suffer if major slop are there mainly due to not being able to repeat your exact hold. In the world of AR's, only the very best of the best will ever be able to wring out all the accuracy that weapon has to give. All that said, if you can prove your being held back by the limitations of the rifle and have exhausted all else, then it wouldnt hurt accuracy. Most uppers and lowers are made to very close and somewhat standardized dimentions. It's pretty rare when the fit is so bad it can have an influence on accuracy. Possible? Yes. Probable? No.
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Yeah, I'll buy that. My thinking runs along the lines that, while it's true that the sights are aligned with the barrel/upper, recoil begins before the bullet exits the barrel, and any variable shifting of the barrel/upper during recoil could lead to variable point of impact. I'm pretty new to the AR world, but that's been my experience with other rifles. One dynamic that might mitigate this is the upper receiver being pushed back and seated firmly against the back end of the lower during recoil. I don't know, it's kind of fun to speculate about this stuff, but as you say, it'd probably take a lot of slop to make a measurable difference, and the amount of play in this case is quite slight. It's too late tonight, but tomorrow I'm going to post some more on this subject, along with specifics on a couple of receivers (with pics of forge marks), on the Rock River forum under "Industry." If you guys get a chance tomorrow afternoon, I'd appreciate your taking a look at that. Thanks very much for your replies. |
| I assembled a RRA CAR A4 upper with a OLL RRA LAR-15 lower and various other RRA parts and the upper to lower frame fit is absolutely perfect as if the weapon came that way. I know it wasnt assembled in the RRA factory but the fit is so seamless i am so glad i DROS'ed the RRA lower when i went to pick up my MEGA lower. I can imagine assembling this upper on any other manufacturer's lower as the fit is that good. I dont think it does alot for accuracy but it definetely does for piece of mind. |
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I have used JB Weld to "bed" receivers. It is quite easy to do, is invisible once assembled and is quite durable. The book Black Magic by John Feamster covers it. You want the JB Weld to adhere to the upper only. Degrease the upper with brake cleaner along the mating surfaces. Coat the lugs and pin holes with paste wax/release agent and coat the entire lower with it. It doesn't take much JB Weld but it must be mixed precisely. Apply very thin coating to the upper mating surfaces, just thick enough to coat. Put a bit more around the front lug area. Let it set up for ~30-45 minutes until it won't sag. Then assemble with an Accu Wedge and let set up. A fired brass case with its mouth sharpened can be used to trim any excess as it won't mar the anodized surfaces. Diassemble, remove Accu Wedge and clean out all extruded material. Any that is visible when assembled should be removed. Discard the Accu Wedge, it is no longer needed! Mine have lasted forever. And like I said, it is INVISIBLE unless you disassemble. Unaffected by any solvent. |
Off the bench is the only place. I might have seen more in standing, if I were in better form with my current CMP SR but I didn't do enough testing. But the USAMU has seen improvement with tight bedded receivers at the 600 yard line where the position is prone and sling tension high. I also like the sealing effect, keeping any gas away from my eyes. |
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