Re: Lapping Compound
Shoes is right.
However, there are those young, headstrong folks who wanna do it anyway.
So, let's deal with a few of the issues.
When to do it? Only after wear patterns on the bolt locking surfaces reveal that large portions of those faces are not engaging. Even then, if the distribution of those wear patterns shows parity between the two lugs, leave it be. The point here is that unless there is evidence of a large disparity in contact, there is no evidence of potential bolt head flex. Unless there's such evidence, there's no reason to lap; normal wear will procede evenly and there is no problem to fix.
What abrasive value is good or bad? In truth the abrasive value only determines how fast the process occurs. Regardless of the abrasive value, the important issue is to keep careful track of the progress. As long as you do this, the faster the better, and no need to finish polish it, normal wear will do this anyway. The other important thing here is to stop when the wear patterns show parity. It's not about getting it all, it's about getting it even.
About honing the lugs and headspace. Yes, headspace will grow. Honestly, even if you abrade the lugs down to where the wear patterns cover 90% of the lug face, we're still only talking about a few thousandths of additional headspace. Handloaded ammo will accomodate this, and probably, commercial ammo will never really be able to tell the difference. Personally, unless one goes hog wild with the abrasion, I think it's a smaller issue.
Still, because of the considerations regarding the ideal way of applying pressure while doing the process, and other issues that make it less than optimal to do without removing the barrel; it's really wisest to leave it to a properly trained and equipped gunsmith.
Greg