A buddy of mine was at range shooting his reloads and had a casing split on him. I guess that's what it's called. No damage to gun but range official asked him not to shoot anymore. Ejected shell and it was opened up on side of casing. What causes this? when he was telling me this, I asked if he measured his casings before actually loading, He said no. I know after shooting that casing will stretch some. I didn't know the answer why I trim mine other than I read it on Aldeer. If the case is longer , what can happen to shell? I told him I always measure before loading and after loading to make sure they aren't over recommended length. I think that's called COL. He said he measures some but not all. What say ye here on Aldeer?

Brass stretched case split. Remember BG your performing a small explosion every trigger pull. I once loaded a .38 special case 122 times before it split a .45 94 times but those are extreme examples. I'd bet Ol'AU338 only gets 5-7 loadings out of his big magnum loads before they work harden and rip.COAL(cartridge overall length) is why we trim.

I had a factory Hornady 45 split it’s entire length a while back. It was one of those nickel plated ones.

The camming action of closing a bolt creates a lot of force, pushing the loaded round into the chamber or pulling the fired case out. If a case is longer than standard length, you can actually "crimp" the case mouth, thus creating extra tension on the bullet. That extra tension raises the pressure and in extreme instances can cause high enough pressure to cause failures.... split necks, split cases, blown primers. Cases grow.... the brass flows/moves in the only direction it can go which is toward the barrel. Everywhere else its contained, by the chamber walls and the bolt face.

If its a good day, you have a bolt that is hard to open and a flattened primer. If its a bad day you get to ride to the ER, and trash your favorite rifle. If its a VERY bad day, you get a ride to the morgue. Don't cut corners. Don't guess. KNOW

Re-reading your post, let me add this: COL or COAL and case length are not the same. COL is the length of the cartridge, which is the length of the case plus the inserted bullet. Case length is the length of the empty case, you should see a "trim to" and a "max length" in the loading manual.

I honestly think nickel plated cases are weaker than standard brass. Loaded some light plate loads in .45 in 55 brand new nickels and every dadblame one of'em split in 4 loadings. 231 and start charge for 200 rn bullet.

That's about right. Start seeing split necks on my magnums on the 6th or 7th load.

When I got my 338 winny back in 97, I bought 100 nickel plated Remington brass to load. It was good stuff, got 7 loads out of it before necks started splitting. It was stretchy, had to trim those cases at least every other firing.

I trash nickel plated .38/.357 because I get 5x times the split cases as from brass. Plus they are much more difficult to size. I check length on every rifle case I reload every time. I shoot semi auto rifles (.223, .308, 30-06) and they are all rough on brass. They slam them in, lock, fire, unlock, and jerk them out with extreme force. Has to be right or there can be a real problem but usually the round won't chamber and lock if the brass is too long. Safer to measure and trim.