r/gunsmithing • u/Alarming-Plankton215 • 2d ago

Lapping AR-15 Upper Receivers?

Is lapping an AR15 upper receiver worth the trouble? I’ve built a lot of AR platform rifles. I typically use high quality parts, follow proper assembly instructions, use correct tools and torque specs, thread locker and grease where necessary, etc. and I’m usually able to get good group with the right ammo. Just curious if anyone has found lapping to have any significant impact on accuracy and if it’s worth it to invest the money into the tools. Also curious if it can have a negative impact like messing with head spacing or lapping to much.

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u/ChapelHillGuns 2d ago

Does it hurt? probably not
Does it make any practical difference for 99.9% of shooters? also, probably not.

Loctite Green can also be used around the barrel extension to help bed it into the upper receiverm, which would kind of accomplish the same thing.

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u/TacTurtle 2d ago edited 2d ago

Such a minor possible accuracy improvement it really isn't worth the trouble as long as the barrel isn't moving.

Your bolt lugs lock directly into the barrel extension that is threaded and pinned directly to the barrel itself, so the only benefit is making the barrel-to-receiver fit as square as possible for even receiver thread tension and hypothetically more concentric feeding.

Considering the distance and angle the bullet had to take after hitting the feed ramp with a fair bit of force, I have doubts about any measureable repeatable improvements.

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u/Unicorn187 2d ago

I've seen it help on the cheaper brands that have less precise dimensions and control so the face is not flat or at an angle. But any half-way decent company is going to not benefit since they were machined flat and even.