Re: Bolt vs accuracy
Bolts should be match-lapped to the extension lugs, or the bolt and extension can be lapped separately to a standard lapping ring or fixture that is hardened. I don't know of any manufacturer that is lapping bolts or extensions and most even fore-go the grinding process as well. I see most manufacturers putting the parts on a lathe after heat-treat and hard-turning the lugs to try and get them to match evenly but this is a fairly crude process; can lead to burrs being formed, cone-shaped faces, out of perpendicularity, etc. Match-lapping needs to be done after heat treat/grinding/shot peen, but before coating; or you can generally re-coat after match-lapping an already coated part.
To answer your question on how important it is to do this process... it depends. It will certainly prolong the life of your bolt, that is a surety. If you currently only have 3 lugs that are making solid contact vs 7 lugs, you get the point. If the bolt/extension lug faces are not parallel with each other then this can tweak case seating to a relative degree. If the lug faces are not perpendicular to the bore center-line, this can have the same effect. Who knows how much that will effect accuracy on your specific barrel setup... I would say none up to 1.5 moa.
If you are seeing that some lug faces on your bolt are shinier than others, then you know the manufacturer didn't do the process right and did not get out all of the heat-treat twisting effect. You have to assume the extension lugs may have the same issue. It's hard to lap an extension that is installed.
