Case Trimming

Brian in Montana

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Ramsay, MT
I feel like I've been posting a lot of dumb questions of late, but here's another:

How much difference does case length actually make? I always measure and trim after every firing, but does it really make enough difference for the trouble it is? Seems like it would effect pressures to a certain extent.
 
Case lengths extending beyond SAAMI specs can supposedly cause safety issues. I trim any new batch of cases to the SAAMI minimum case length and don’t need to trim again for several firings depending upon the cartridge. I’ve never found a change in velocity or accuracy as the cases get slightly longer, but I still always measure the cases to make sure they are within specs and within a few thousandths of each other. Neck sizing dies also help decrease stretching in cartridges such as 22-250 that are tapered and tend to stretch more than others.
 
I use the Lee trimmer system. I trim every single time. Accurate ammo is made by keeping all factors the same. The Lee trimmer makes trimming and chamfering simple. No measuring needed, it stops cutting when they are the right length.
Does it matter a lot most of the time? Not unless they are overly long as to cause a pinched bullet in the throat, or not allow the bolt to close.
But , it's not much trouble to me for the piece of mind it gives me.
You'll find some cartridges and loads need trimmed often anyway.
 
Case lengths extending beyond SAAMI specs can supposedly cause safety issues. I trim any new batch of cases to the SAAMI minimum case length and don’t need to trim again for several firings depending upon the cartridge. I’ve never found a change in velocity or accuracy as the cases get slightly longer, but I still always measure the cases to make sure they are within specs and within a few thousandths of each other. Neck sizing dies also help decrease stretching in cartridges such as 22-250 that are tapered and tend to stretch more than others.

If the cases get too long they may not chamber at all or if they are forced into the chamber, when fired the neck may not be allowed to expand enough to release the bullet, then you got major pressure problems.
 
I use the Lee trimmer system. I trim every single time. Accurate ammo is made by keeping all factors the same. The Lee trimmer makes trimming and chamfering simple. No measuring needed, it stops cutting when they are the right length.
Does it matter a lot most of the time? Not unless they are overly long as to cause a pinched bullet in the throat, or not allow the bolt to close.
But , it's not much trouble to me for the piece of mind it gives me.
You'll find some cartridges and loads need trimmed often anyway.

Or one can use a junk case to make a trim to length dummy cartridge and use it to set your trimmer. A .30-06 dummy case will work for .25-06 and other .30-06 based cases. I have a file type .30-06 trim die which I've used just a few times. Somewhere along the line one needs something to use to set up the case trimmer.
 
So I feel like I should know this, but I don't. Is the "trim length" published in manuals intended as a maximum, a minimum?
 
What manual are you using? The 308 win max case length is 2.015 and the minimum case length, sometimes referred to as “trim to” length is 2.005.
 
The drawings are typically maximum SAAMI length. As mentioned there is often a trim to length listed. I believe the Lee trimmer pilots are setup to trim well short of SAAMI.

You may also find a lot of new brass to actually be short. Typically I trim to the shortest of my batch when starting new and trim after several firings to keep things just below SAAMI in an attempt to keep things consistent. I've been told having a consistent neck length helps with consistent neck tension (same amount of brass contacting the bullet) though neck thickness, type of sizing die used, seating die setting, etc also come into play so there are a ton of variables there.


I shoot a lot of once fired 5.56 brass and will process a pile of range brass as well as once fired I have acquired from friends. I started using the Frankford Arsenal Case Prep Center. It indexes off the shoulder of the case. It takes a bit of finesse at first but once you start it'll make short work of 500-1K pieces. My bigger cartridges like 300WSM and straightwall cases (which almost never need to be trimmed) get trimmed on a lyman setup. I've all but stopped using Lee case trimmers due to the volume I tend to process at one time.
 
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I use the Lee trimmer system. I trim every single time. Accurate ammo is made by keeping all factors the same. The Lee trimmer makes trimming and chamfering simple. No measuring needed, it stops cutting when they are the right length.
Does it matter a lot most of the time? Not unless they are overly long as to cause a pinched bullet in the throat, or not allow the bolt to close.
But , it's not much trouble to me for the piece of mind it gives me.
You'll find some cartridges and loads need trimmed often anyway.

Lee's trimming setups (shell holder and case length gauges) are really slick. It doesn't take long at all to trim and chamfer during case prep. I just chuck mine in my drill.
 
I am sure ,trimming more than a hundred or so at a time would be easier and quicker with a power case prep machine.
The ones I have looked at run around $160.00-$200.00.
The Lee trimmer is around $12.00 for the tool and 6-7 bucks for each caliber specific pilot.
I never load more than a couple hundred rounds at a time, and more often 50-60 every so often .
I'll spend the extra money on bullets and powder.
 
Lee's trimming setups (shell holder and case length gauges) are really slick. It doesn't take long at all to trim and chamfer during case prep. I just chuck mine in my drill.

Agreed. I have used them for years. I got a Lyman case trimmer, that belonged to my dead brother-in-law. After using it, I went back to my Lee trimmers. They are cheap, simple and fast-when used with a drill.

Most manuals give a max case length and the casing does not have to be trimmed if it is below this. That being said, I rarely push them to the max. I trim after a couple firings for the most part.
 
I use an RCBS case length trimmer...takes a minute to get it set for the cartridge. But I believe it improved my hand loads consistency over something like the Little Crow Gun Works "WFT" which trims off the shoulder. I'm now a believer in trimming based on overall case length measured from the case head.
 

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