Question about trimming pistol cases

[rlbellco72]

Bare with me as I am just getting into reloading.

I have read on two different forums about trimming pistol cases and the general consensus is that semi auto cases don't need to be trimmed and that revolver cases sometimes need to be trimmed to acheive a good crimp.

I guess, I just want to get a third opinion, from my fellow VGOF members.

Also, any advice about reloading would also be appreciated. I currently setup to reload .40 S&W and .38 Special.

Thanks

[noylj]

All cases start out slightly too small.
Bottleneck cases, because pressure against the shoulder causes the case to stretch, need to be trimmed every three or so firings.
Straight-wall cases, since there is no shoulder pushing the case forward, do NOT grow. Thus, they don't need to be trimmed. With many firings, most straight-wall cases, in fact, seem to shrink a bit.
Revolver cases, that head-space on the rim, are trimmed just so the roll crimp is consistently in the crimp groove. Once trimmed, they are good-to-go from then on.
Semi-auto cases that head space on the case mouth should not be trimmed and, if accuracy is your goal, you will be best served by actually measuring the cases after sizing and saving those that are within 0.005" of the max length for your "match" loads.

[rlbellco72]

Thanks for the feedback noylj.

[jdonovan]

I have read on two different forums about trimming pistol cases and the general consensus is that semi auto cases don't need to be trimmed and that revolver cases sometimes need to be trimmed to acheive a good crimp.

We teach students in the reloading class to always measure.

While it is possible they may need to be trimmed, and I've had some new factory brass that could have used a few thou taken off, I've never trimmed a factory ammo case in my life. And thats been over 20 years on the SAME 38 special cases.

You need a caliper to set OAL any way... check your brass it only takes a few seconds, and you don't have to measure every one of the cases. A 5-10% sample will generally be enough for brass that you have been keeping together as a batch as you'll be keeping records of case length change. If you're using random range pickups, then you need to be more careful.