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Hi all! Nice site here! I was wondering, if I shut off my gas valve on my M1a, and shoot a round, will the brass that I eject by hand reveal the headspace measurement of my chamber? I`m trying to size my brass giving .003" headspace clearance, but its hard to get an accurate measurement from my regular ejected rounds, because the measurements are all over the place. Thanks a million!
 

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Fatelvis,

Not sure if that'd work or not, but I might have to try it sometime. I noticed that my fired brass had about a 6-8 point spread on the RCBS precision mic. I ended up stripping the bolt, and then sizing brass to let the bolt close freely. Even sizing dies seem to have a variable, though: the dies ended up being screwed in a tad to account for that. It'd be interesting to see what you find out.
 

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Just strip your rifle and bolt and size your cases down till they just fit the chamber with only light finger pressure on the bolt lug. Just as you would for a bolt action. Size them no more and no less. There is an article on my website describing how I do it in detail. The case mics are about worthless in my opinion. Your chamber IS your gage!
Once you get your sizer set locktight it down permanent and only use it in that gun from now on. It's doubtful the setting will ever change through the life of your barrel.
 

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Dan's method is much more preferable for this check.
I've made the mistake a couple times of forgetting to open the gas valve at the range - and it WAS a mistake. Somtimes that bolt will lock in REAL tight - so much so that you have to pound on the op rod to get it open....................NOT a good choice.
 
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