Lapping upper receiver

I have a few aero precision upper receivers and my ?? is do I need to lap them or does it matter?

I would lap them, there is always a little bit of an issue. I think it helps the barrel nut seat better anyways, anything that makes the bolt lock and release better eliminates future problems.

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Why would anything need lapping? I’m lost on this.

It eliminates canting of barrel extension in receiver.

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I started doing it on all my builds and have yet to find an upper regardless of make that doesn’t need it to some extent, just some more than others

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Does the factory do this before shipping? QC…