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+--- Thread: Lapping ar15 uppers (/showthread.php?tid=20459)
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Lapping ar15 uppers - Msalm - 02-04-2020
I do feel the shrink fit method or shimming for tight fit in the upper has a lot of merit, but I have had great results with just facing the upper and bedding that I have not played with other methods. For bedding I just use red loctite, vs an actual bedding compound. After removing a couple after assembly years later I see no need to do it any other way. The loctite fills any gap and hardens into a ‘shim’ of sorts. Has to be heated and driven out to replace and I feel it does a great job.
Lapping ar15 uppers - Mesa1978 - 02-04-2020
I did it to a DPMS slabside with a Wheeler and blue loctite in 300 BO, it is a parts leftover assembly, so no loss if it was a mess. I get 3/4 moa at 100 yards with a YHM can and factory 190 subs, so no complaints, no idea if the added prep made a difference.
I did the lapping to VLTOR uppers with a Shilen and a Lilja barrel, both in 6.5 G, didn't need it in either case, uppers were square.
The VLTOR I used with a Stoner (Liberty) 24" 5R barrel shoots 3/4 moa at 100, with nothing more than just attaching the barrel and proper torque, so I'm not an advocate, lapping and bedding done well, it probably doesn't hurt anything.
Lapping ar15 uppers - mdram - 02-05-2020
from arfcom, in case you are not there or didnt see it
https://www.ar15.com/forums/ar-15/Barrel-handguard-crooked-/118-743023/
https://www.ar15.com/forums/ar-15/Crooked-handguard-barrel-follow-up/118-748246/
TLDR: barrel was offcenter, rail manufacturer (midwest ind) offered to look at it, determination was upper (spikes) needed lapping, they lapped it for him
Lapping ar15 uppers - guitarhillbilly - 02-05-2020
I had a machinist friend lap my upper on a surface lap table and check it with the optical flatness method.
https://en.wikipedia.org/wiki/Optical_flat
Lapping ar15 uppers - Mad Charlie - 02-08-2020
The Flats will tell you if the surface is flat, but it won,t tell you if it is square to the centerline of the barrel, by itself anyway.
Lapping ar15 uppers - dlraymond30 - 02-27-2020
I have always lapped any uppers that don't require heat to drive the barrel ext into them I use shim stock and green loctite after freezing the barrel and heating the receiver. I'll bet I can shoot a few rounds with no barrel nut attached they're so tight lol... I wouldn't try it but I bet I could