I am new to reloading for .308win. Can someone explain to me why you need to trim case from the maximum case length of 2.015 to 2.005? Is this to allow for neck expansion during firing? How far above or below the trim to length value can I vary? Do new brass need to be trimmed to 2.005? Thanks!
Question on OAL and Trim to Length
- Thread starter Ngyukon
- Start date
Everytime you fire a round, the case "flows" a little bit forms to the chamber. Then once you resize the brass it gets worked once again. All these things over time lengthen the case. If it is not kept in check, the case mouth will eventually bottom out on the chamber, in the worse case actually pinching the bullet and cause pressures to rise upon firing. Hence trim them back. We usually do new brass just to make them uniform.
You trim to length so you are not jamming the case onto the rifling which will greatly increase your pressure. Your cases will grow more by resizing them, then by shooting them. I trim my .308 to 2.000 and can go 5-7 firings before they need to be trimmed again.
Please correct me if I am mistaken. I thought the suggested trim to length for .308win is 2.005 which is the minimum. The maximum being 2.015. Basically, if my case length is anywhere between 2.005 to 2.015 it will be safe?
Is it safe to trim to 2.000? or how far below 2.000 can I go?
Is it safe to trim to 2.000? or how far below 2.000 can I go?
Yes.
Don't panic if you get to less then 2.005 on some cases but I wouldn't get unnecessarily experimental without good reason and more experience
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Maynard just told you it was safe!
It is interesting to note that Maynard is a top of the line match shooter, and he has just said the cases can vary in length to the order of .010".
Why do new reloaders and plinkers make so much of a few thou difference in case length? (Except, as has been adequately pointed out, don't let them get too long.)
How far below 2.000 can you go? It is not uncommon to form 270 W brass from 30-06 brass. The newly formed 270 case will be about .10" (100/1000 of an inch) shorter than the specified length of a 270 case. They shoot just fine and will eventually grow to full length, or even to where they need to be trimmed.
Another rule of thumb to use, for casual shooting, at least, is the neck has to be long enough to firmly hold the bullet.
I am using an .308 Obermeyer match chamber and have not problems trimmed to 2.000". Like I said I can get 5-7 loadings before I have to trim again, so that just means one or two more firings between trimming. I have had cases as long a 2.017" before trimming.
