Posts: 153
Threads: 7
Joined: May 2018
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.
Posts: 259
Threads: 4
Joined: May 2015
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.
Posts: 941
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Joined: Sep 2016
from arfcom, in case you are not there or didnt see it
https://www.ar15.com/forums/ar-15/Barrel...18-743023/
https://www.ar15.com/forums/ar-15/Crooke...18-748246/
TLDR: barrel was offcenter, rail manufacturer (midwest ind) offered to look at it, determination was upper (spikes) needed lapping, they lapped it for him
Posts: 33
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Joined: Feb 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
Posts: 830
Threads: 31
Joined: May 2017
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.
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Joined: Nov 2018
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
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