I made my own for every type of action I fiddle with. Just a tennon that threads into the action and shoulders against the receiver with a brass spring loaded plunger attached.
If your rifle is on the long side of acceptable headspace and your lugs are grossly out of whack, then I guess it is possible to knock the gun out of H/S. Good lord though, you'd have one serious case of carpal tunnel/arthritis/tennis elbow by the time you got there. Unless your using driveway gravel for lapping compound.
The tools do work and it saves time. Also does a better job because it'll emulate a cartridge's behavior when under pressure. It is possible to side load a little bit when just doing it by hand. Bear in mind though that most "reasonably tight" actions the clearance is around .003" to .005" from bolt to receiver bore. Take a bolt that is around 6.5 inches long inside the bore and we are only talking about a maximum deviation of .04407 degrees (2 minutes, 38 seconds if my conversion is correct) Going the other way, the very outer edge radius of the bolt lug is out of parallel with the receiver's lug surface by only .00038". To put it in perspective, that's like taking a single yellow "post it" and splitting it just over ten times.
Engineers (whom I love to plagiarize) use this term called "down in the mud" meaning mathematically, it is able to be solved/found, but its so minuscule that its not really worth getting excited over.
I've always sorta viewed lapping lugs as more of a quality control/inspection process than really attempting to gain performance from it. Especially when you consider that both lugs aren't touching with the gun in battery anyways.
Last edited by NesikaChad; 08-05-2008 at 12:41 AM.