Accuracy change 45ACP 45 Auto rim

Vet66 · September 30, 2015, 05:35 PM

Same load and coal same bullet, yet the auto rim is all over the place compared to the ACP brass in a S&W 625 PC. Why?

Kosh75287 · September 30, 2015, 06:34 PM

What kind of dies are you reloading the Auto Rim rounds with? Are they the .45 ACP dies, used to reload your ACP cases?

Vet66 · September 30, 2015, 08:04 PM

Quote:

What kind of dies are you reloading the Auto Rim rounds with? Are they the .45 ACP dies, used to reload your ACP cases?

Yes, they are the same dies with minor adjustments.

jag2 · September 30, 2015, 10:32 PM

So you are using moon clips on the 45 ACP rounds? What are you doing for a shell holder, did you order one specifically for the 45 auto rim? Is your coal staying consistent, checking a lot of them throughout the loading session? Those are the only things I can think of. I use the same rounds for revolver or semi auto, just use moon clips in my 25-2 with no problems.

Vet66 · October 1, 2015, 08:22 PM

Well of course you change the shell holder for auto rim brass, much thicker rim. I'm using the auto rim brass to eliminate the moon clips used for ACP brass. The question is why the change in accuracy between the brass, same volume ?

Hunter Customs · October 2, 2015, 08:06 AM

Maybe case mouth tension, either from not sizing enough of the case or the difference in the crimp pressure.
I would try roll crimping the auto rim brass if you are not doing so already.

**Unclenick** · October 2, 2015, 09:23 AM

I would take fired rounds and weigh the cases and expended primers, then fill them with water and weigh them again. Subtract the dry weights from the wet weights to make sure the internal case volumes are actually the same. Since the brass forming steps are different, they may not be.

I would also measure loaded rounds as to thickness of the brass over the bullet to see if the rattle room is similar.

After those checks, though, assuming they don't produce anything obvious, I'm going to guess that the moon clips are actually helping center the cartridges in the chambers when the firing pin goes forward. Particularly if the bullets are lead, this will affect accuracy by mitigating how tilted the bullets are when entering the forcing cone, something that can increase groups size significantly. This is why, with lead bullet revolvers, you always see the advice to size the bullets to fit the chamber throats within half a thousandth if you can. That lines them up and eliminates tipping.

Assuming that is the actual problem, another thing I've found helpful is using a stepped expander like the Lyman M type to provide the case mouth flare. This creates a step that you seat the bullet into so it starts straight into the case during seating. You can see the effect by examining the slight bulge line in the brass where the base of the seated bullet stops. Using a belling flare, that line is frequently uneven to the point you see it only on one side of the case and not on the other, and more so in some individual rounds than in others, indicating variable degrees of bullet tipping. But using a stepped expander and setting each bullet squarely into its stepped flare, the seated bullet bulges are much more uniform all around, indicating less tilt in the bullet.

Vet66 · October 2, 2015, 10:48 AM

Unclenick, thank you for your informative reply. I will try all as you suggest. The bullets I am using are poly coated lead 200gr SWC pushed by 4.0gr of VV N310 powder and, CCI primers.

September 30, 2015, 05:35 PM	#1
Vet66 Senior Member Join Date: October 31, 2014 Location: Pennsylvania Posts: 187	Accuracy change 45ACP 45 Auto rim Same load and coal same bullet, yet the auto rim is all over the place compared to the ACP brass in a S&W 625 PC. Why?

September 30, 2015, 06:34 PM	#2
Kosh75287 Senior Member Join Date: October 15, 2007 Posts: 820	What kind of dies are you reloading the Auto Rim rounds with? Are they the .45 ACP dies, used to reload your ACP cases? __________________ GOD BLESS JEFF COOPER, whose instructions, consultations, and publications have probably saved more lives than can ever be reliably calculated. DVC, sir. انجلو. المسلحة. جاهزة. Carpe SCOTCH!

October 2, 2015, 09:23 AM	#7
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	I would take fired rounds and weigh the cases and expended primers, then fill them with water and weigh them again. Subtract the dry weights from the wet weights to make sure the internal case volumes are actually the same. Since the brass forming steps are different, they may not be. I would also measure loaded rounds as to thickness of the brass over the bullet to see if the rattle room is similar. After those checks, though, assuming they don't produce anything obvious, I'm going to guess that the moon clips are actually helping center the cartridges in the chambers when the firing pin goes forward. Particularly if the bullets are lead, this will affect accuracy by mitigating how tilted the bullets are when entering the forcing cone, something that can increase groups size significantly. This is why, with lead bullet revolvers, you always see the advice to size the bullets to fit the chamber throats within half a thousandth if you can. That lines them up and eliminates tipping. Assuming that is the actual problem, another thing I've found helpful is using a stepped expander like the Lyman M type to provide the case mouth flare. This creates a step that you seat the bullet into so it starts straight into the case during seating. You can see the effect by examining the slight bulge line in the brass where the base of the seated bullet stops. Using a belling flare, that line is frequently uneven to the point you see it only on one side of the case and not on the other, and more so in some individual rounds than in others, indicating variable degrees of bullet tipping. But using a stepped expander and setting each bullet squarely into its stepped flare, the seated bullet bulges are much more uniform all around, indicating less tilt in the bullet. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

September 30, 2015, 10:32 PM	#4
jag2 Senior Member Join Date: June 30, 2009 Location: dallas Posts: 773	So you are using moon clips on the 45 ACP rounds? What are you doing for a shell holder, did you order one specifically for the 45 auto rim? Is your coal staying consistent, checking a lot of them throughout the loading session? Those are the only things I can think of. I use the same rounds for revolver or semi auto, just use moon clips in my 25-2 with no problems.

October 1, 2015, 08:22 PM	#5
Vet66 Senior Member Join Date: October 31, 2014 Location: Pennsylvania Posts: 187	Well of course you change the shell holder for auto rim brass, much thicker rim. I'm using the auto rim brass to eliminate the moon clips used for ACP brass. The question is why the change in accuracy between the brass, same volume ?

October 2, 2015, 08:06 AM	#6
Hunter Customs Senior Member Join Date: March 26, 2005 Location: Osborn, Missouri Posts: 2,697	Maybe case mouth tension, either from not sizing enough of the case or the difference in the crimp pressure. I would try roll crimping the auto rim brass if you are not doing so already.