In the case of rimmed cartridges, variations in case length would seem to make little difference in perrformance except that amount of roll-crimp that the crimp die imparts would be greater for slightly longer cases, etc. I guess it follows that pressure could be affected likewise.
On the other hand, semi-autos (.40S&W, .45ACP, etc.) which head-space on the case neck - hence the reason for taper-crimps - would seem to be very particular about length variation. If case is too long it won't chamber; if too short you get a dud.
Having said all that, I use .40 brass as it comes from the dumpster, and have never had a missfire on that account. Would I be better served by measuring and trimming, etc. (I like the Lee system on other calibers.) or should I be satisfied if it goes bang following trigger pull?

Would seem to be a great waste of time to me.....
Randy

In my life time I have loaded many thousands rounds of pistol ammo and I have never trimed a single case. I also would say that 97% of the brass that I have reloaded are range pick up. Don

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"Don't worry be happy"

I trim and chamfer my pistol cases.
But then I hand-weigh each charge.
I count stairs (over and over and over).
I read Moby Dick once a year.

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and what his trumpet saith

Who really goes down with the whale: Ahab or Starbuck?

Everybody, save only one.

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and what his trumpet saith

I have seen no appreciable difference when trimming pistol cases other than in producing rounds. If they aren't too short, and they are for a semi-auto and they go bang......um.......why bother?

Just a while ago, I wanted to do a test. Trimmed 100 45ACP brass, loaded them all the same at the same time with bullets from the same casting session, same sleeve of primers, the whole nine yards. No difference across the chronograph, none. On the target, no difference. In the press? Yeah, nice flares and crimps every time.

FWIW

I'm with Hawkeye10, been reloading for 35+ years, many thousands of rounds, have never trimmed a case, and have never had a problem.

I trim them, but I don't lead a very exciting life.

I measure and trim when needed but then I usually strive for quality over quantity too. Different strokes for different folks as the old saying goes. Do as you wish and as long as it works for you you are good to go.

I'm one of those 30+ years reloading guys and never once found a need to trim any of my pistol or revolver brass. As long as it chambers properly, the wobble errors I induce when attending to make it go bang, are of far greater significance than any inherent advantage I've ever been able to demonstrate on another of the fascinating minutia of reloading.

Rifles do need trimming from time to time.

I have bench rest friends whose lives would be in shambles if they were somehow prevented from performing their own rituals....but they ain't hand gun shooters.

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Dum vivimus Vivamas

In loading and shooting several hundred thousand straight-walled pistol rounds, I have yet to see the need to trim a single case. Revolver brass tends to wear out before it's needed, and many semi-auto cases (most notably the 45ACP) tend to shorten with use, given standard-pressure loads. The cartridge length of a 45ACP is listed as .898, I have yet to see one that was actually that long, most are .892-.895".

As was said, the difference in accuracy from round to round is far less than my own variations from shot to shot.

I have never trimmed pistol cases in 30 years of shooting BUT I did stay at a holiday inn once.

I thought the Lee trimmers were a good idea, because I had trouble with the base and crank things on rifle cases.
I bought one for every handgun caliber when I ordered one time.
Sat down and went through bunches of brass in several calibers.
Didn't get a single sliver of brass.

I had to trim all my 9x18 Makarov cases, but then I was making them from 9x19 cases. Other than that, never trimmed one.

I guess some fanatical match shooter who deburrs and bores all primer holes to exact sizes might trim cases for the sake of consistant lengths, but most likely not.

The crimp on straight wall cases often need trimming, i.e. .357, .44 mag, hot loads in the special's. My .44 mag loads "stretch" the brass and have to be trimmed to get a uniform crimp.

One trimming is good for 3 to 4 loadings. If I load to the mild side, trimming is not necessary for me.

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JIM
NRA Pistol Instr

And do you wear a belt and suspenders? Actually, there is something very satisfying knowing you have a box full of perfectly loaded ammo! I do that with my 454's but not with my 44 mag and 38 spl.

I reload only 45 ACP for my M1917 and M1937 and I trim cases just to keep mouth square. I've noticed most cases shot once are out of square and it hurts my sense of the perfection.

Agree with Cochise especially with .44 mag hot loads, and .357 too. Trim to get uniform bullet seating and crimping on the cannelure. Max with H110 seems to give some stretch.

"Call me Fishmeal."

The only pistol cases I trim are the ones I shoot in Revolver category (.44 Mag) in handgun metallic sihouettte shooting. Target ranges are 50 - 200 meters. I leave my case trimmer set to the same length, and every case gets a little brass removed after each firing, almost always on one side of the mouth. Trimming squares up the mouth and gives me a consistent crimp. My match loads group about 3" at 100 yards out of my revolver.

I've never trimmed any case for a semi-auto.

Color me anal, but I do trim the flash holes and length of new
.44 brass. Thereafter maybe every 5 loadings do they stretch
enough to need another trim. .44 spl almost never need a trim
after the initial cleanup.

I have noticed that headspace is very poorly controlled in most
revolvers and this can contribute to case stretching. I bought
some snap caps that don't even begin to intercept the firing
pin. I complained and they told me they were "in spec" listing
dimensions that varied dozens of thousandths of an inch.
For the record these are A-Zoom .44 spl. I am going to try the
Triple K next.

6mm needs a trim after 3 or 4 shots. I have several weapons
in this calibre, all with different chambers, and don't want to exceed max length.

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Nemo