Trimming Pistol Brass


October 29, 2009, 06:23 PM
I am looking at getting some pistol dies. I was wondering if I need to also get the case length gage so that I can trim the brass. I am interested in 9mm, .45GAP, .45ACP, .357mag, and .38spcl. The 9mm, .45ACP, and .45GAP will be used in semi auto pistols while the .357 and .38 will be used in revolvers. Do I need to trim the brass? What are the pros and cons of doing so? Thanks.

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October 29, 2009, 06:36 PM
I've never trimmed 9mm 38 special or 357 mag

load shoot enjoy

Jim Watson
October 29, 2009, 06:38 PM
I once trimmed a big bag of mixed .357 Magnum brass so the hard roll crimp I wanted on a heavy load would be uniform. Otherwise, I don't bother.

October 29, 2009, 06:41 PM
what kind of loader are you getting

I have a single stage and a progressive. I have loaded about 3000 9mm rounds so far and lots of 38 special

October 29, 2009, 06:48 PM
I've never trimmed pistol brass. For heavy crimps with a revolver, maybe. Depending on what I'm using it for. If I was trying for the tightest groups at 100 yds, it probably would make sense. For the go-fast, under 30 yd shooting I do, I couldn't possibly notice a differece.


October 29, 2009, 06:48 PM
I don't trim straight wall handgun brass.

October 29, 2009, 07:13 PM
The only advantage of trimming pistol brass is that you can get the crimps exactly the same (as Jim W notes above). Fortunately, there is hardly ever a need to get crimps this uniform, and hardly anyone trims pistol brass. If you aren't absolutely sure that you need to trim your pistol brass, then you don't and you probably never will. Don't worry though, there are plenty of other things you can spend $$$ on when you handload!

October 29, 2009, 07:26 PM
I never trim auto pistol brass. I do trim revolver pistol brass because it helps give more uniform crimps, especially critical (IMHO), if you are roll crimping.

October 29, 2009, 07:48 PM
I never trim my pistol brass wether it be auto or revolver, taper crimp or roll crimp,
don't matter, never a problem, been doing it for 54 years.

October 29, 2009, 09:10 PM
If you want to trim, the Lee case length gauge sets are cheap and work well.


October 29, 2009, 09:40 PM
Bottlenecked brass extends after firing. If you do not trim it, it does not chamber perfectly, which affects accuracy at first.

Straight wall brass shortens after firing. My 9mm brass, which was .752" unfired, is shortened to .744"-.738" after being fired 2-10 times. I wish to have something that would extend the 9mm brass back to its original length.

October 29, 2009, 11:21 PM
I trim my .38 Super cases once just for accuracy, not sure if it helps, but I feel better. No trimming on 9mm or .45acp. I probably should on my .357 mag cases, but haven't. I use a light crimp for light loads there.
If you don't have calipers, get one, they can measure a lot of things besides case length.

Steve C
October 29, 2009, 11:33 PM
Pistol brass gets shorter with use so you can trim virgin brass, after that it shrinks so there's no reason to. I bought one of the Lee case trimmers for .46 acp, .367 and .38 spl when I was new to reloading. Used it once and never bothered after that since the cases wouldn't trim with its fixed length insert.

Rifle cases grow in length because of the greater pressure. I'm not sure about the "super mags" like the S&W 500 etc. as they operate at rifle pressures.

October 29, 2009, 11:52 PM
I just alternate shooting my .357 between my puma and my 971. :D

October 30, 2009, 12:16 AM
Rifle cases grow in length because of the greater pressure. I think it may not be just pressure, but also shape of the brass. Shoulder at the bottlecked case may not perfectly fit the chamber. When firing, it enlarges main part of the case to the chamber, thus moving brass material towards case neck. Resizing of the brass upon reloading does not move the brass material back to base. Instead, it just shrinks the diameter making case shoulder thicker, and extending case length, thus requiring trimming after a while. This does not apply to straight-wall cases.

October 30, 2009, 01:43 PM
I check all pistol and revolver brass for maximum length, and set aside those that need trimming.
I assemble nearly all revolver ammo with cast lead bullet that have a crimping groove in the design. Case length is critical for crimping into this groove.
I check all semi-auto pistol cases for maximum length, then set aside those that require trimming. In my experience, the 9mm Luger is the worst offender, especially if the cases are of foreign manufacture.
The .45 ACP rarely requires trimming. Once in a great while I find a single case out of hundreds that's a little long.
On revolvers, the .357 Magnum seems to require the most trimming, I've found. I shoot almost exclusively lead bullets, requiring a roll crimp into the groove.

Interestingly, the worst offenders I've found for being overly long are factory-new, unfired .30-30 and .32 Winchester Special brass. One of my older Speer reloading books cautions shooters to watch for empty .32 WS brass being too long.
I size all brass, even new unfired stuff, before loading and then check case length for trimming -- handgun and rifle brass. I never assume that the factory got it right. If you've ever been in a munitions plant, and see how quickly brass disks are made into cases, you too would wonder how in the devil we get such uniform cases from such mayhem.
But we do. Nonetheless, there's a margin of error in everything, even nature -- they're called mutations.

I've been reloading for nearly 40 years. I check brass length religiously, and trim as needed. Others may consider it a waste of time with handgun brass, but it makes me feel safer about my reloads.
Whether it makes for more accurate ammo is probably moot: these 54-year-old eyes ain't what they used to be. Time was, I could spot a pretty woman in a blue dress at 200 yards. Today, I'm more inclined to see a mailbox at 50 yards, squint, and think she needs to go on a diet! :D

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