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-   -   Trimming and Crimping (http://www.firearmstalk.com/forums/f30/trimming-crimping-20253/)

TXnorton 11-20-2009 01:20 PM

Trimming and Crimping
 
Specifically 9mm and .45 ACP, and more specifically on a progressive press.

What do you folks do with regards to case length trimming and crimping?

When using my old single stage RCBS press, I would, as a standard practice, trim every case after de-capping and re-sizing regardless of actual length. Then I would set the bullet seating / crimp die for the trimmed case length.

With my new RL-550B I am wondering if I have been overly anal about this (probably - I am an engineer).

I now have the separate crimping dies for the 4th stage of the Dillion, and I have the bullet seating die screwed out 2 turns so as not to crimp as per the Dillon instructions.

How sensitive is the case length to the set point for the crimp die? There is a .010" dfference in the specified "max" and "trim to" case lengths for these two calibers.

I know that you do not want to have excess case length as these cartridges head space on the case rim.

Should I worry about this at all, beyond trimming cases ONLY if they exceed the maximum specified case length? Do you set the crimp die for a "mid-range" case length?

robocop10mm 11-20-2009 02:42 PM

I do not recall EVER trimming (or even measuring case length) a rimless pistol case. Length rarely changes enough to matter on a straight walled case like this. For that matter I do not even trimm Magnum revolver cases.

Bottleneck cases will stretch, partially from the higher pressures and partially from the nature of the expander ball being drawn through the case after sizing.

I have loaded and fired 10s of thousands of rounds of handgun ammo and have never had a length related issue. By the time a handgun case stretches to the point is should be trimmed, it is usually cracked and in the recycle bin.

RCHanlin 11-20-2009 03:11 PM

Quote:

Originally Posted by TXnorton (Post 188518)
Specifically 9mm and .45 ACP, and more specifically on a progressive press.

What do you folks do with regards to case length trimming and crimping?

When using my old single stage RCBS press, I would, as a standard practice, trim every case after de-capping and re-sizing regardless of actual length. Then I would set the bullet seating / crimp die for the trimmed case length.

With my new RL-550B I am wondering if I have been overly anal about this (probably - I am an engineer).

I now have the separate crimping dies for the 4th stage of the Dillion, and I have the bullet seating die screwed out 2 turns so as not to crimp as per the Dillon instructions.

How sensitive is the case length to the set point for the crimp die? There is a .010" dfference in the specified "max" and "trim to" case lengths for these two calibers.

I know that you do not want to have excess case length as these cartridges head space on the case rim.

Should I worry about this at all, beyond trimming cases ONLY if they exceed the maximum specified case length? Do you set the crimp die for a "mid-range" case length?

I used to do the same thing when I was loading with single stage press. It's only after I got my progresive rig that I realized that my cases did not require trimming. I still check batches for case length just to be sure though usually after they come out of the tumbler..

cpttango30 11-20-2009 03:13 PM

pistol brass will fail long before they need to be trimmed. I started doing it at first then I figures out real fast that was useless endeavor.

JonM 11-20-2009 04:10 PM

Quote:

Originally Posted by TXnorton (Post 188518)
Specifically 9mm and .45 ACP, and more specifically on a progressive press.

Should I worry about this at all, beyond trimming cases ONLY if they exceed the maximum specified case length? Do you set the crimp die for a "mid-range" case length?

i crimp all ammo that is used in semi automatic weapons and magazine fed bolt rifles that are not being used single shot at a time. i set my crimp to be a middle of the road. a little heavier or a little lighter doesnt matter much in a semi auto.

when i load my .308 for accuracy loads i use no crimp as that ammo never sits in the magazine and is loaded and fired in the rifle one at a time.

TXnorton 11-21-2009 10:54 AM

I did some experimentation on the 9mm cases (my .45 ACP's were already reloaded):

I measured about 30 random 9mm cases BEFORE resizing, and then again after re-sizing. The cases do "grow" in length when resized from .005" to .008".

My own prior reloads: Before re-sizing average = .736" after re-sizing average = .744"

Range pick-up (first fired) brass: before re-sizing = .741" after re-sizing = .746"

Published maximum case length for the 9mm is .754"

Published trim to length is .744"

All re-sized brass was well below the maximum case length. My prior reloads were from 20+ years ago, and I may have trimmed them back then, but I cannot remember. IF so, and as they (my prior reload cases) measured (on avergae) to 0.744" after re-sizing, that is what I would have trimmed them to back then and then this could verify that there was no (significant) case length growth due to re-firing and re-sizing.

I would guess that when fired that the cases expand in diameter and "shorthen" in length, then when resized they return to spec case diameter and "grow" back in length. What I have not done is fired a set of cases where I had actually pre-measured the sized cases before shooting and then again after re-sizing to see if there is any "net" growth in case length.

As you can see, I am still being anal. Well, it was a rainy day, and I did not have anything better to do with my time.

Robbo, you answered my question on case growth in bottle-necked rifle cases. Before I learned that you needed to trim the cases, I had stuck an overly long .223 case in my AR-15. That was almost 30 years ago and it was a real pain - live round partially chambered, bolt not fully closed and I could not get the bolt open or the round out of the chamber (no range rod at hand). That experience resulted in me becoming very paranoid about case trimming. But I think you are right and straight walled pistol cases should not be a concern.

Thanks,

robocop10mm 11-21-2009 02:35 PM

Oh I understand anal. That and OCD are actually desirable characteristics for handloaders.

On that out of spec .223 case - You were lucky it would not chamber. I saw a nice Colt A-3 blow up mostly because the brass had not been trimmed. The mouth was forced into the throat and pressures spiked. Cracking a barrel extension takes about 80,000 psi.

JonM 11-23-2009 09:53 PM

if you realllllly wanna learn the true meaning of anal retentive go talk to a benchrester for a bit ;) they make monk look like a slob.


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