02-05-2012, 02:51 PM
elkbow Wrote:it doesn't take but slight torque change in an action screw in a bolt gun to affect accuracy, on an AR, your lower is dangling from your rest, if you have a light trigger and only pull the trigger without holding the grip, there would be little affect in accuracy, if you hold the grip while shoot and there is play front to rear, you can affect accuracy....
this could be argued to death, i've built over 20 AR's and owned I don't know how many, i've seen about everything from cheap parts being good to good parts being cheap, I can't say that i've sat down with each AR and checked for accuracy by adjusting the upper to lower receiver fit, however I have seen where a sloppy front takedown pin affected accuracy twice, and I replaced with tighter fitting pins or used shims from triggershims.com, for most purposes though for the average shooter, they don't care about bedding, shims, tight fighting parts, if their gun will shoot 1 MOA they are good to go, I won't own a gun unless it will shoot .5 MOA or better with my handloads....well I should say that, my stock 450 bushmaster uppers shoot just under 1 MOA with factory ammo, bought the Hornady stuff for $19 a box and don't plan to reload for awhile and haven't spent enough time with my 458 SOCOM, it shoots right at .75 MOA with 300gr TTSX and should have put on one of Marty's barrels, just using the RRA barrel, so might not get down there, but shots will be limited range anyways
I know this could be argued to death, but i'm anal about mechanical stuff, i'm an engineer
Elkbow,
I'm an engineer too, and agree with you in theory, but in practice it just isn't so. I've seen some of the sloppiest fit AR's, ones that audibly rattle, win national championship matches in the hands of the top AMU shooters. I can guarantee you that if accuwedges, bedded or bolted, or just selecting tight fit upper to lowers, made a difference, they would do it, money is no object, time is no object for them. But instead they concentrate on quality components and tuned loads. Even the tuned loads is to the average upper, not an individual one.
The AMU also has a ganged machine rest that clamps the upper receiver into a return to battery recoil guide type of fixture that uses just a trigger housing to fire the uppers, so there is no lower even in the equation. The best shooting one goes to the top shooter regardless of lower fit, that's how they get the sloppy fit to begin with. To them knowing their trigger is a higher priority than the fit, that's also why they shot Geissele High Speed triggers, and as nearly identical as they are they won't trade lowers to get a better fit for fear of changing the trigger release they have trained with.
I know this because I have dryfired some of their rifles and asked how they can live with that slop. They just smile and say look at the scores I just shot with that sloppy fit.
Regardless of all that I still like a tight fit, and have ordered Les Baer matched upper and lower halves for my next build.
Bob