1911Forum - View Single Post - Hey Steve! (in Allentown), What about 9's & 10's?
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Old 01-22-2020, 09:46 PM
BBBBill BBBBill is offline
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Originally Posted by Jolly Rogers View Post
Why would case length matter? Rim thickness from base to extractor grove should be the determining factor.
Originally Posted by Steve in Allentown View Post
Here are the optimum hook-to-breechface distances provided by log man:
  • 9mm - .060"
  • 40 S&W - .065"
  • 45 ACP - .075"

Here are the SAAMI specs for rim thickness from base to extractor groove:
  • 9mm - .050"
  • 40 S&W - .055"
  • 45 ACP - .049"

I'm not seeing the correlation between rim thickness and hook-to-breechface distances. That distance may be more of a function of the angle at which the rim begins moving up behind the extractor. That angle would be influenced by the length of the cartridge. I'm just speculating here. Where are the engineers when you need them?
Originally Posted by Robin Hood View Post
Exactly, the longer the case or fatter, the more room needed for the rim to articulate into position behind the extractor hook.

IME The rim doesn’t just pop straight up parallel with the inner face of the extractor hook, they have to rotate up into position somewhat. Longer the case and bullet or fatter in diameter, the more room for articulation into place. I use .068” at least with .075” working just fine for .38S with the appropriate extractor hook shape and don’t get any rim bite, anything smaller and the rim gets chewed up a bit.
Just to add to the confusion, I believe that our departed master smith, Jerry Keefer, used something around .067-.068 for .45ACP on his builds. I know, I know. Don't compare his builds to anyone else's. They were engineering masterpieces.
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