.45 acp chamber taper??

Swilly · January 21, 2014, 12:48 AM

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.

**Unclenick** · January 21, 2014, 10:19 AM

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.

Clark · January 21, 2014, 11:05 AM

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.

Swilly · January 21, 2014, 02:57 PM

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.

January 21, 2014, 12:48 AM	#1
Swilly Member Join Date: January 14, 2014 Location: Central, WI Posts: 18	.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.

January 21, 2014, 10:19 AM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	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. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 21, 2014, 11:05 AM	#3
Clark Senior Member Join Date: December 4, 1999 Location: WA, the ever blue state Posts: 4,678	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. __________________ The word 'forum" does not mean "not criticizing books." "Ad hominem fallacy" is not the same as point by point criticism of books. If you bought the book, and believe it all, it may FEEL like an ad hominem attack, but you might strive to accept other points of view may exist. Are we a nation of competing ideas, or a nation of forced conformity of thought?

January 21, 2014, 02:57 PM	#4
Swilly Member Join Date: January 14, 2014 Location: Central, WI Posts: 18	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.