Case Trimming

Roninco

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May 7, 2020
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Colorado
How much less than your actual chamber length should you trim your cases? Or do you just go by the trim length recommendations in reloading manuals?
 

Roninco

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May 7, 2020
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Colorado
I have the Sinclair case length gauges and I do anneal. Not sure I want to trim every time. Just wondering how much less is a reasonable trim length.
 

rsmithsr

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Oct 29, 2019
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455
Location
phoenix
the "normal" is 10..but normal chamber has 25 or so beyond the normal case length.
my chambers are cut with a short oal neck.
 

Litrfoot

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Jan 9, 2019
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45
Location
California
The best way, if you are shooting SAMMI spec chamber and cartridges, is to look up on the SAMMI website and find your camber print. There will be two prints, one for the chamber and one for the cartridge. On the cartridge print you will find the max length, then look at the chamber print and it will show the distance to the 45 degree cut before the throat. That is generally 10 thousands but not always, sometimes more, sometimes less. So what you want to avoid is during firing, the neck stretching and hitting that 45 degree taper and pinching the neck down and creating a pressure spike. This can be more critical with a 20 degree shoulder vs a 30 degree or greater shoulder due to stretching of the brass. Bottom line, at the max trim length you will have plenty of room to spare, but you must pay more attention to your brass length, maintaining that trim length. Hope this helps?
 

rsmithsr

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Joined
Oct 29, 2019
Messages
455
Location
phoenix
not true
sammi is a lot more than 10 between chamber and case at the neck length.
the trim spec is 10 but the actual distance is much more

The best way, if you are shooting SAMMI spec chamber and cartridges, is to look up on the SAMMI website and find your camber print. There will be two prints, one for the chamber and one for the cartridge. On the cartridge print you will find the max length, then look at the chamber print and it will show the distance to the 45 degree cut before the throat. That is generally 10 thousands but not always, sometimes more, sometimes less. So what you want to avoid is during firing, the neck stretching and hitting that 45 degree taper and pinching the neck down and creating a pressure spike. This can be more critical with a 20 degree shoulder vs a 30 degree or greater shoulder due to stretching of the brass. Bottom line, at the max trim length you will have plenty of room to spare, but you must pay more attention to your brass length, maintaining that trim length. Hope this helps?
 

GLTaylor

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Oct 11, 2019
Messages
567
Location
Cedar Bluff, Al
Your cases shouldn't stretch enough to make you trim every firing. The worst i ever had was a std 243. It and other cases with similar shoulder angles frequently require trimming every 3-4 firings. That's the reason I went to the 40° Ackley shoulder. It Really Slows down case stretching!
 

MagnumManiac

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Joined
Feb 25, 2008
Messages
2,268
I measure my chambers neck length.
My comp barrels are normally around .040” longer than the max cartridge length...so I trim to be .005”-.010” of that length.
I anneal every firing and trim every sizing.

The worst case I have EVER worked with for case growth was the 375H&H...hence why I re-chambered to 375 Bee. Even after fire forming which SHRINKS the necks by .030” on average, the cases take a LONG time and many firings to grow back to even the trim length.

The AI’s are similar to this too.

Cheers.
 

tnek13

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Joined
Feb 26, 2012
Messages
139
Location
NW Indiana
I use Little Crow trimmers. I set them to trim a couple of thousands less than max and trim after every sizing.
 
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