The true M14/M1A match chamber is a short chamber: headspace is very tight. That’s because Lake City Match ammo is short. Compare this to what you might want to use, and if you have a genuine match chamber, best make sure the ammo fits… Measure both the results of sizing operations and also any new ammo or brass before you fire it in one of these chambers! I have encountered commercial .308 Win. rounds that were too long out of the box (cartridge case headspace dimensions). Here’s a cartridge headspace read on a Lake City Match compared to a commercial Winchester match load (inset) I had on hand. Read taken with a zeroed Hornady LNL gage. And NEVER fire commercial ammo intended for hunting use; the component mix and round structure is almost certain to be wrong.