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Chamber Headspace

Chamber Headspace

Check It

Certainly, if you do your own barrel installations, safety of the end result is of crucial importance. Of course it is. I really don’t think turning your head, closing your eyes and firing a new installation from the hip into the dirt constitutes a certifiable safety check. Well, OK, laugh (it was supposed to be funny), but I’ve had people tell me that’s what they do….

It’s true tolerances among parts are generally tight enough that swapping bolts and bolt-carrier assemblies normally won’t result in parts pairings, resulting in a headspace concern. Question is how you value the difference between supposing and knowing. We get pretty complacent after enough builds because it is very unusual to encounter a problem using mil-spec and commercially-produced bolts and barrels.

Get The Tools

Since headspace checks are easy enough and a pair of gages is an easy enough investment, I surely recommend this routine to anyone who works at all with barrels and bolts. You will need to know what you’re looking for before you invest in a gage set. By that I mean the chambering specifications you are out to confirm. There are huge differences in NATO and SAAMI-spec .223 Remington chambers.

Headspace, in essence, is the distance from the bolt face (when the bolt is in battery or fully forward, rifle ready to fire) to the location of the “datum line” along the case shoulder. On .223 Remington, this line is a .330″ diameter. Height to this line will be in the vicinity of plus 1.4636″ (SAAMI headspace spec). When the chamber reamer is run, the builder or manufacturer stops forward progress of the cutting tool with respect to this. Headspace can vary a little from maker to maker depending, among other things, on their beliefs as to what “playing it safe” means.
If the reamer were run too far, then the datum line measure would be farther into the chamber. That would allow too much room ahead of the cartridge case shoulder, and that defines excessive headspace. If the reamer wasn’t run far enough, then the height to the datum line would be shorter, and that is insufficient headspace. Both are bad. Excessive headspace opens up the potential for a case failure, what we can call “blowed-up.” Insufficient headspace means the bolt might not close fully on a chambered round, and that opens up the potential for an out-of-battery discharge, what we can also call “blowed-up.”

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