Real case trimming effects

[Thor2j]

Does anybody have any data of trimming their cases to the same length vs letting them be what they are as long as they dont exceed the chamber length.

Reason being that I have done it both ways and see little difference. I've measured my chamber length and am no where near that length but the brass ranges from 2.0245" to 2.0315" for twice fired Lapua .260. The new Lapua brass averages 2.0280". The average of the twice fired Lapua brass is probably 2.0285". I dont want to trim them all to 2.0245" because that is my shortest and would make them all the same because I feel thats a waste since the average is much longer. I am shooting out to 1000 so maybe the smallest differences would help. I'm leaning towards trimming them all to the factory 2.0280" and letting the short ones hopefully stretch. Any input would be great, thanks!!!

My measured chamber length is 2.0590", then for some reason sinclair recommends subtracting .024 thus my max trim to length would be 2.0466".

 

[ksthomas]

Thor2j,

The obsession with case lengths (down to .0001") seems to be a recent preoccupation, and I really don't know where it comes from. It's a waste of time. Case trimming for most bottlenecked rifle cartridges is a matter of safety, to ensure that the case mouth doesn't encroach on the leade just ahead of the chamber mouth. To do so may allow the chamber to actually "crimp" the case against the bullet, offering some very real pressure problems. Trimming them back to a point where they don't do this, is the goal. I've routinely trimmed my 308 Win cases back to 2.000" even, some .005" under the "suggested trim length" listed in most manuals. Those trim lengths, incidentally, are routinely nothing more than .010" below the SAAMI or CIP "Max case length" for a given cartridge, or 2.015" in the case of the 308 Win.. Nothing magical about the number, and it really has little to no effect on accuracy with this type of case.

In cases which are crimped, particularly with a roll crimp or something similar, uniform case length helps to ensure consistent crimp pressure and neck tension . . . vitally important when loading your NM Model 94 .30-30 lever action for an upcoming 1,000 yard BenchRest match . . . if you get my drift. Don't sweat it. Just make sure they're not encroaching on that chamber mouth, and you're good to go. Spend the time and concern on other things that really matter, but trimming ain't one'a them.

 

[Thor2j]

Thor2j,

The obsession with case lengths (down to .0001") seems to be a recent preoccupation, and I really don't know where it comes from. It's a waste of time. Case trimming for most bottlenecked rifle cartridges is a matter of safety, to ensure that the case mouth doesn't encroach on the leade just ahead of the chamber mouth. To do so may allow the chamber to actually "crimp" the case against the bullet, offering some very real pressure problems. Trimming them back to a point where they don't do this, is the goal. I've routinely trimmed my 308 Win cases back to 2.000" even, some .005" under the "suggested trim length" listed in most manuals. Those trim lengths, incidentally, are routinely nothing more than .010" below the SAAMI or CIP "Max case length" for a given cartridge, or 2.015" in the case of the 308 Win.. Nothing magical about the number, and it really has little to no effect on accuracy with this type of case.

In cases which are crimped, particularly with a roll crimp or something similar, uniform case length helps to ensure consistent crimp pressure and neck tension . . . vitally important when loading your NM Model 94 .30-30 lever action for an upcoming 1,000 yard BenchRest match . . . if you get my drift. Don't sweat it. Just make sure they're not encroaching on that chamber mouth, and you're good to go. Spend the time and concern on other things that really matter, but trimming ain't one'a them.

Thanks for reinforcing what my test data shows, not much difference in the trimming.

 

[ksthomas]

No problem, and glad to help!