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Old January 21, 2014, 12:48 AM   #1
Join Date: January 14, 2014
Location: Central, WI
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.45 acp chamber taper??

Does anyone have any good theories as to why saami specs for a .45 acp chamber call for .007" taper from case mouth to breech face? I am assuming that it is to facilitate easy extraction in an auto pistol but seems overboard as all of the 5 different brands of factory ammunition I have mic'd come in at .470-.4715 and many have been smaller at the web.
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Old January 21, 2014, 10:19 AM   #2
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From the SAAMI drawing, I get 0.0030" taper on the cartridge case and 0.0052" taper on the chamber. This is for the 0.650" separated reference points. The taper's a little bigger all the way from the case mouth to the breech.

That is, as you suggest, for feed reliability, as is the unsupported portion of the standard barrel. Keep in mind that, like any military gun, the 1911 had to pass sand and mud contamination functionality testing, so it couldn't be as tight as you'd design a target pistol.
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Old January 21, 2014, 11:05 AM   #3
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In December 2000 I built a 45acp with a Shilen .451" groove barrel black on a 1903 Turkish Mauser action.
For a reamer I used a .469" straight fluted reamer and a 45acp throater.
I chose .469" because brass that went through a Lee .457" Carbide die ring [45acp carbide sizer die], came out at .469".
I then throated until a dummy round with a 230 gr FMJ seated to 1.275" would just allow the bolt to close.
Loaded to 460 Rowland levels, the rifle shoots small groups at 100 yards with 230 gr FMJ bullets, but not very good with 185 gr.

What does it all mean?
There is no taper.
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Old January 21, 2014, 02:57 PM   #4
Join Date: January 14, 2014
Location: Central, WI
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Thank you guys for your input.

My mauser's chamber has a very small amount of taper. Just what was honed into it. It was bored however as it saved the trouble of making a reamer. I figured I could get away with a much tighter chamber in a bolt action.
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45 acp , chamber

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