I'm hoping for some help from the Hide on finishing a pure precision ar grendel for a split hunting and competition build. I understand the instinct to give "the difference is negligible" and "it doesn't matter" responses, and generally I appreciate them. However, the fun of building an AR for me is truly tuning everything to be as absolutely accurate as possible for whatever purpose it is that I built the gun. For this gun, I am shooting for absolute maximum precision out to at least 700. So, this thread is for the min/max'ers out there who understand the obsession with mechanical perfection notwithstanding cost or otherwise external limitations.
At this point in the build, my question relates to ideal handguard and upper receiver mating. My 6.5 CM ar10 was built somewhat early in my progression through the hobby, so I just threw a Bartlein on a thermofit upper (BCM I think). It was a tack driver (1/3-.5 moa gun), but on loading a bipod there was a slight POI shift and even some spreading of the groups. I swapped out the BCM upper and put it on a monolothic billet upper/handguard system. The barrel fit wasn't as snug, but I still lapped and bedded it with shims, etc. The POI issue disappeared completely, but the groups spread out slightly and I attribute this to the fact that the barrel wasn't in a super tight upper (though it was shimmed to be very tight).
Now I am trying to build the perfect 6.5 Grendel, and torn as to whether there is a larger benefit to the thermofit upper or the increased rigidity of an upper that connects directly to the handguard (Seekins IRMT-R, Larue Stealth 2, Aero enhanced, monolithic uppers to the extent they are still in production). Has anyone experimented with the two enough to build an opinion on which is better? Better yet, does anyone know of a manufacturer that has both very snug, preferably thermal-fit uppers with a compatible rail that connects directly to the upper as to create a truly free-float rail system that does not touch the barrel nut?
It appears based on the options, I am forced to decide between very tight uppers and a more monolithic rail system, but I would love to be corrected if I am wrong. I also know that the geiselle rails are said to be great, though they aren't truly free float. Does anyone have an opinion as to whether the added rigidity of geiselle's proprietary barrel nut outweighs the potential rigidity benefits of a connected upper/handguard set?
And finally, another accuracy element I have not attempted to reduce before is the negative impact on accuracy that results from play between the BCG and the upper. For this build I am going with a JP LMOS bcg and enhanced bolt, so I am hoping this isn't an issue. However, I know that Wilson billet uppers have tighter tolerances inside the upper to remove the play of the BCG. The wilson upper, however, is not monolothic and has no options for direct attachment to the rails.
Current build thus far:
20" Proof SS straight-taper barrel (will be shimmed for the build) with rifle length gas
JP LMOS bcg and enhanced bolt
Master of Arms adjustible gas block
Battle arms lower
Triggertech diamond trigger
A2 stock with either Taccom lightweight buffer system or JP SCS
all the other stuff that doesn't matter. Just can't decide on the upper, handguard and barrel nut
Advice would be hugely helpful. Apologies for the long-winded question, and thanks in advance
At this point in the build, my question relates to ideal handguard and upper receiver mating. My 6.5 CM ar10 was built somewhat early in my progression through the hobby, so I just threw a Bartlein on a thermofit upper (BCM I think). It was a tack driver (1/3-.5 moa gun), but on loading a bipod there was a slight POI shift and even some spreading of the groups. I swapped out the BCM upper and put it on a monolothic billet upper/handguard system. The barrel fit wasn't as snug, but I still lapped and bedded it with shims, etc. The POI issue disappeared completely, but the groups spread out slightly and I attribute this to the fact that the barrel wasn't in a super tight upper (though it was shimmed to be very tight).
Now I am trying to build the perfect 6.5 Grendel, and torn as to whether there is a larger benefit to the thermofit upper or the increased rigidity of an upper that connects directly to the handguard (Seekins IRMT-R, Larue Stealth 2, Aero enhanced, monolithic uppers to the extent they are still in production). Has anyone experimented with the two enough to build an opinion on which is better? Better yet, does anyone know of a manufacturer that has both very snug, preferably thermal-fit uppers with a compatible rail that connects directly to the upper as to create a truly free-float rail system that does not touch the barrel nut?
It appears based on the options, I am forced to decide between very tight uppers and a more monolithic rail system, but I would love to be corrected if I am wrong. I also know that the geiselle rails are said to be great, though they aren't truly free float. Does anyone have an opinion as to whether the added rigidity of geiselle's proprietary barrel nut outweighs the potential rigidity benefits of a connected upper/handguard set?
And finally, another accuracy element I have not attempted to reduce before is the negative impact on accuracy that results from play between the BCG and the upper. For this build I am going with a JP LMOS bcg and enhanced bolt, so I am hoping this isn't an issue. However, I know that Wilson billet uppers have tighter tolerances inside the upper to remove the play of the BCG. The wilson upper, however, is not monolothic and has no options for direct attachment to the rails.
Current build thus far:
20" Proof SS straight-taper barrel (will be shimmed for the build) with rifle length gas
JP LMOS bcg and enhanced bolt
Master of Arms adjustible gas block
Battle arms lower
Triggertech diamond trigger
A2 stock with either Taccom lightweight buffer system or JP SCS
all the other stuff that doesn't matter. Just can't decide on the upper, handguard and barrel nut
Advice would be hugely helpful. Apologies for the long-winded question, and thanks in advance