It's very helpful, Tuner, as always.
So no one should worry, this is NOT a real gun, just an example with minimum dimensions I made up to be sure I understood the various relationships involved with headspacing, and with the unsupported section of the chamber.
Still, I see now why you frown on cutting the barrel so close to the limit. I thought about tolerance stacking, and slide-slap with the barrel lugs(part of firing-locked hs), but I confess I didn't think to consider wear, stretch, flex, and the like, nor about case web variance. Not to mention much used cases. It wouldn't take much to get into dangerous territory, NOT good.
Is there a spec for chamber minimum supported length at the 6:00 position? There must be, but how the devil would you measure it? - about the only way I can think of is with casting alloy (Cerro Safe or such).
Also, while you are very right to warn us never to rely on it, wouldn't the ammo manufacturers allow for some level of wear, out-of-spec barrels, max headspace, etc. in their case design?
(Got another question about lug fitting, later on)
Once again, priceless, and thank you.
Bookmarks