Of those who lap your AR uppers (specifically, the mating surface which contacts the barrel extension for headspace), has anyone seen any variability between specific manufacturers and their tolerances/QC in this dimension?
I am simply curious and figure this will make for interesting convo…
I personally have seen great variability in uppers, all from a single manufacturer, when lapping. Though, I have yet to do before and after testing to verify efficacy.
Hopefully someone can chime in and provide some input for you.
Several Aero & PSA and one unknown brand, no difference to me, they all lapped about the same! I do question if it really makes a difference, I also bed the barrel with blue loctite… i think I’m just wasting my time but since i have the equipment I might as well do it !
I might try a differently marked upper on the next few scratch builds then. I’ve done all palmetto uppers, both built and stripped, and have actually torn them down to lap. I really should do a before and after… it seems on every lapping job with their receivers the high spot is towards the same direction, but the amount of lapping needed to get at least 2/3 contact area seems to always be very different.
It may or may not be a wasted effort, but I do it for fun anyway. The more things you “need” to do to a rifle, the more time you “need” to be working on them. 
Aero, BCM, Rainer Arms, LaRue, Cross Tool & Machine, PSA, Colt…( probably forgotten some brands ) all have benefited from Lapping for me. Large Frame and Small Frame.
Have any of them been consistently better then the others… no… not in my experience.
They have all varied.
Ironically, when I sat down to do all my spare uppers, one of the PSA ones needed the least lapping. No kidding.
I don’t feel it is a result of poor machining, I do believe it is more a anodizing issue. After talking to someone that does anodizing for a living, he said anodizing doesn’t apply evenly, and can vary even dependent on its position in a anodizing tank.
Huh… that’s good info to know. Thanks, bfoosh!
As bfoosh006 said I always lap my upper revievers. It doesn’t matter who the manufacturer is. It is a cheap and simple process to do so why wouldn’t you do it. When you want the best build possible it is cheap insurance just to do it. Little things really start to add up to overall build quality when you are building a new project.
Does anyone have any links to a good video explaining “lapping”? I’m new to the AR platform, but currently have 3 builds underway. This is the first time I’ve come across this topic. It hasn’t popped up in any of the research I’ve done thus far.
Thanks
https://criterionbarrels.com/media/accurizing-the-ar-15-video-series/?v=00dc5da36527
Part 3 , about the 44 second mark.
I seen lapping before, but never really researched it more as it seemed a bit unnecessary. I am doing my first build soon and wonder if I should bother with it. How would one know if I need to do it and wouldn’t taking off the coating make for a weak point against rusting?
While I understand lapping for precision varmint guns or precision long range, on standard defensive or 3 gun ARs it is equivalent to adding a glass pack to a Civic, the gains are minimal for the time and effort expended.
That said, if you have your own tool, do it! Regardless manufacturer you should take your upper down and ensure proper grease/fitment etc., anyhow personally
then again, I had a few ARs I just used and they worked fine without any breakdown or fitting/lapping
You are exactly correct. The lapping tool is cheap and the lapping process only takes a few minutes to do. If I didn’t have my own tool I wouldn’t take it to someone to have it done. If you are planning on building several AR or helping other people out then pick up a lapping tool. It is simple, easy and quick.
I plan on doing this to my uppers. I just need to find the time.
The interface of the barrel extension with the upper receiver has nothing whatsoever to do with headspace. Headspace is controlled by the barrel extension and bolt dimensions.
I ended up realizing that well after starting this thread. Thanks for the clarification for everyone!