1911 9mm Headspace

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1911 9mm Headspace

Post by Bigtrout on Thu Jul 23, 2015 9:32 am

The SAAMI spec for 9mm Luger brass length is 0.754 (-0.010).  I've measured the length on once-fired cases and constantly get 0.743 to 0.744 in. on 5 different manufacturers.   Since the cases headspace on the mouth isn't there an accuracy issue with these cases being at the low limit and slightly under that limit?  Has any one done go-no go headspace gauging on their 1911 9mm?  Maybe I'm being too picky but it seems odd that the cases aren't hovering around 0.749 in.  

I know pistol cases shorten with firings but I find no length difference between once and twice- fired cases.   Any data, threads, opinions or comments out there?  Thanks.

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Re: 1911 9mm Headspace

Post by Jerry Keefer on Thu Jul 23, 2015 9:54 am

Bigtrout wrote:The SAAMI spec for 9mm Luger brass length is 0.754 (-0.010).  I've measured the length on once-fired cases and constantly get 0.743 to 0.744 in. on 5 different manufacturers.   Since the cases headspace on the mouth isn't there an accuracy issue with these cases being at the low limit and slightly under that limit?  Has any one done go-no go headspace gauging on their 1911 9mm?  Maybe I'm being too picky but it seems odd that the cases aren't hovering around 0.749 in.  

I know pistol cases shorten with firings but I find no length difference between once and twice- fired cases.   Any data, threads, opinions or comments out there?  Thanks.
Same with the 45 ACP
If you are seeking maximum accuracy, minimum headspace is desired. Select cases to be used exclusively at 50 yards.. Cut the chamber to compliment that case length.. Shortline is not as critical , and just about any decent case can be used.
I don't deal with 9mm any longer, but Starline brass is the longest, and most consistent for the. .45. I have not compared that with the 9mm but I would hazard a guess that Starline would be your best choice.. I too find no truth to the straight wall cases growing shorter in the .45
Probably due to the lower pressures used in Bullseye loads..

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Re: 1911 9mm Headspace

Post by noylj on Fri Jul 24, 2015 9:52 pm

I use a L-SWC that just "kisses" the lede/rifling/lands for head space control and that generally is also the most accurate COL.
If you really want to worry about it, get 9x21 cases and trim so the case exactly fits your gun's throat/lede--it will exceed SAAMI max case length, but as long as you don't use the cases in a shorter chamber, you're good.

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Re: 1911 9mm Headspace

Post by Jerry Keefer on Fri Jul 24, 2015 10:10 pm

noylj wrote:I use a L-SWC that just "kisses" the lede/rifling/lands for head space control and that generally is also the most accurate COL.
If you really want to worry about it, get 9x21 cases and trim so the case exactly fits your gun's throat/lede--it will exceed SAAMI max case length, but as long as you don't use the cases in a shorter chamber, you're good.
Noylj...
Using the projectile as a cartridge stop is not headspace..
A true match chamber will be designed around a projectile / case combination.. The case mouth on a 9mm or 45 should stop against the chamber edge..The bullet should have no influence what so ever on the cartridge resting position within the chamber..I believe in some freebore, and 1-1/2 degree leades to insure there is never any restricting contact..  The amount of headspace is then the clearance between the cartridge base and the breechface..There are various opinions as to the best amount of headspace..
SAAMI spec is a poor indicator, and I base it off the brass that is available.. Starline offers the longest brass. Therefore, I set my chamber depth accordingly.

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Re: 1911 9mm Headspace

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