308 case trim ?

[dom350]

Good evening - I am new to reloading rifle cartridges - been reloading pistols for awhile and I finally got a case trimmer to start in on the rifle side.

Here is my question. I just went and fired about 40 308 rounds and I went to trim them per the specs in my lynman book. It says this

Cast Trim length = 2.005
max case length = 2.015

Most of my case are between 2.003 and 2.004. I was under the impression that they stretched during discharge. These are factory rounds, just fired. Am I missing something here???

[nemesiss45]

They probably just trimmed them short at the factory. Reload them, shoot them, then see where they are at.

Also, did you size before measuring? They should stretcg in sizing.

[Blindstitch]

Several manufacturers use undersized or THEIR Size brass. I'm sure there are a few reasons why but I can't think of any besides maybe being able to use the same projectile across a huge line of ammo.

Some cased don't stretch all that much the first few firings but i'm sure after you reload this brass a few times you will be able to worry about trimming.

[Jim243]

In some of the lager calibers it is not unusual for the case to get shorter. The case will expand laterally to fill the chamber. Depending on how generous the chamber has been reamed cases will shrink in the overall length. I find that this is true in 243 cases and unless they have significantly shrunk, I do not worry about it but just resize the case and use again. Your only concern is that there is sufficient neck length to hold your bullet in with sufficient neck tension to insure that there will be no setback of the bullet while in the magazine, to help insure that I usually crimp with a Lee Factory Crimp die, be sure not to put a roll crimp on the case since that will lesson the neck tension.

Good luck and stay safe.
Jim

[Bart B.]

Virtually all bottleneck cases are shorter after firing. They lengthen when resized. My .308 cases shorten about .003" when fired then lengthen about .004" when full length sized. They grow about .001" each time.

I trim mine to 2.000" then when they've grown to about 2.010" after several shoot and full length size cycles, then trim 'em back to 2.000" and start over.

[Slamfire]

Most of my case are between 2.003 and 2.004. I was under the impression that they stretched during discharge. These are factory rounds, just fired. Am I missing something here

I cannot remember a time where once fired and once sized 308 was not over maximum. What counts is the length after sizing.

Trim length is primarily a safety consideration. You don't want the case mouth to stick out in the throat and pinch the bullet. As long as the case neck holds the bullet, even if the neck is excessively shortened, all that will happen is that the bullet goes down the barrel. Might lose some shine to the chamber neck if thousands of excessively short cases are fired, but, might not.

[Blindstitch]

What cases are you using since they can be different from different manufacturers.

[dom350]

Okay - I did not resize them first... Sorry for wasting everyones time. I will resize then measure, then trim if needed. Thanks for everyones quick input and responses to get me back on track.

[Blindstitch]

Hey don't forget to come back and give us the measurements.

[dom350]

After Full length re-sizing all the cases needed to be trimmed. How often do you guys use a uniformer? I have never used one on pistol rounds but it seems?? to be common on rifle cartridges.

[nemesiss45]

Uniformer as in flash hole uniformer?

[Bart B.]

Flash hole, primer pocket and neck wall "uniformed" are sometimes used in the pursuit of accuracy. I don't think they're needed until your worst groups through 300 yards are 1/3 MOA, 1/2 at 600 and 2/3 at 1000. Maybe not even then. Spend your resources on the other 99% of tiny groupsmanship. Otherwise, their usefulness will be masked by other things; bullet-barrel/groove diameter mismatch, for one. Not squaring up bolt and receiver faces for two others.

[dom350]

Flash hole, primer pocket and neck wall "uniformed" are sometimes used in the pursuit of accuracy. I don't think they're needed until your worst groups through 300 yards are 1/3 MOA, 1/2 at 600 and 2/3 at 1000. Maybe not even then. Spend your resources on the other 99% of tiny groupsmanship. Otherwise, their usefulness will be masked by other things; bullet-barrel/groove diameter mismatch, for one. Not squaring up bolt and receiver faces for two others.

Can you elaborate on the last two items? I've googled them both and it doesnt return good results.

[Bart B.]

bullet-barrel/groove diameter mismatch. . . Bullets need to be a few ten-thousandths larger than the barrel's groove diameter for best accuracy. If undersize, they'll deform enough to be very slightly unbalanced.

Not squaring up bolt and receiver faces . . . Squaring up the receiver face lets the barrel seat tight and evenly all the way around where it presses hard against the receiver. If not, a high point with most force puts a stress there as the barrel heats up. The barrel bends a little and shot impact starts moving away from point of aim. Bolt faces squared up keeps case heads square with the chamber axis. If they're not, the case head slams into the edge of the bolt face off the recoil axis causing the barrel to whip more in that direction before the bullet leaves; not good for one hole accuracy.

[dom350]

Thanks Bart!