Yesterday's Weapons Forums

me too, i really enjoy getting these bits of info, i realize you have accumulated it from years of experience and that is an extremely valuable commodity

Gary, does the polish or finish on the chamber affect the ease of extraction in this type of rifle?

Question 2: Does successive firing increase the diameter of the bulge or does the bulge increase in front to rear contact area? I have never checked it. Just wondering.

Older Navy:

I don't have the experience of a gunsmith to intelligently talk about chamber condition causing extraction problems, but I'm sure it can occur. Usually extraction problems result from:

a. Ammo problems

b. Mechanical problems in the weapon other than the finish of the chamber, like a broken extractor or some problem with the breech face (bolt) that causes the case to go off kilter and get out from under the extractor hook.

When the barrel is installed in a rifle, there is a finishing step where the chamber is reamed and polished to set the correct headspace. In an arms factory, this is just part of the manufacturing process and is done routinely all the time. For this reason, surface condition of the chamber usually isn't problematic (but like any other human endeavor, can be subject to error). Chamber finishing problems usually occur when local gunsmiths or do-it-yourselfers are involved.

Naturally, there are all kinds of things that can happen to chambers after the rifle leaves the factory, usually involving rusting in some form. Chambers can be re-polished to eliminate this as an extraction problem.

When I was in Vietnam, I was issued an M-60 MG for guard duty once that had rust in the chamber and it caused extraction problems big time.

Question 2: That little bulge or ring at the base of the cartridge case stays put. Once it is fired the first time, it's there and stays there. It doesn't grow forward on the case. The small base dies will iron it back flat most of the time. I have never sectioned a rifle chamber, then carefully measured it across from back to front (or vice versa). I'm just going to guess here, but I think if we did section one, we would find that the tolerances are closer at the forward end and looser at the rear. This only makes sense. This is because they need to be tighter at the forward end for proper bullet alignment on the bore centerline, and for gas sealing. On the other hand, if the tolerances were close all the way to the breech face, you might never get a fired case out of there.

When you think about it, proper sizing of a rifle chamber is a very precise matter. Just right here, just right there, and too much or not enough anywhere and it's no good.

I use the Lyman small base dies for .223/5.56mm. Had all kinds of problems in my AR chambering round loaded with the standard RCBS dies.

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