Trimming cases that headspace off the mouth

[mattri]

Just put together a little project running a 350 Legend on a Savage platform and have run in to an interesting situation.

When cases are fired, then trimmed to length/chamfered/cleaned etc, then re-sized the sizing process invariably bumps the case mouth back up a little, slightly changing the COL from the already trimmed (proper) length. As this round, and many others headspace off the mouth this can create an interference issue akin to not properly bumping back the shoulder on a bottleneck case.

It seems the best route is to re-size the case first, then trim to length.

I'm new to straightwall cases that headspace off the mouth so maybe this is what you guys have been doing all long.

Is this all there is to it?

Thanks, Matt.

[ak_milsurp]

Yup

Sent from my LM-V350 using Tapatalk

[mattri]

Well man did I overthink that. Alright then, thanks

[ShooterAZ]

The sizing process tends to stretch them a little, but the firing process can actually cause some straight walled cases to shrink a little too. As long as you're not over the Max COAL everything should be fine. You did answer your own question, size first then trim.

[mattri]

Thanks guys!

Related question:
How short is too short?

I realize there is a max length we don't want to exceed so we trim to length x- and that sometimes straight wall cases will as mentioned actually shorten somewhat. At what point do they become too short?

We have a max length, do we have a minimum?

[WHITETAIL]

Most strait walled cases are trim to .010 shorter than MAX.

[Winger Ed.]

I trim after sizing on rifle ammo, but never bother trimming straight wall handgun stuff.
They headspace off the mouth of the case, but there is a tolerance too.

They'll still work if they are a tiny bit longer than they're supposed to be, unless you have a real short chamber.
If they're a tiny bit too short, the firing pin will push them up some, but it still has enough over travel to make a good strike.

[dtknowles]

Trim after sizing because that is the condition of the case when it is chambered.

Tim

[Texas by God]

The trimmer pilot won’t fit in a sized case, will it? Or am I thinking of bottleneck rifle cases? I never trim .30 Carbine, 9mm Luger, or .45 ACP- but the .350 Legend was the topic. Never mind....

[mattri]

Actually that's what started this whole thing.

The pilot will fit inside the neck of a fired bottleneck cartridge but once sized it won't- so you trim first then size.

Well I just found out the same is true with the 350 Legend. The trim pilot fits inside a fired case but if you trim then size the case stretches and you're back past your trim-to length. In an AR style chamber you have enough "slop" it doesn't really matter but in a tighter chamber you can run into an interference.

Looks like I'll just need to thin the trim pilot down a touch.

[dtknowles]

Have you tried trimming after you run the case on the expander? Size, expand, trim, chamfer, prime, charge, seat, (maybe crimp), shoot.

[BrutalAB]

I mostly load straightwall cases and always thought the proper way to trim any case was to do it after sizing for this reason. I trim my bottleneck rifle rounds after sizing for this reason. Never thought the issue wouldnt exist on bottlenecks... learn something new every day.

Edit to add:
A little lube on the pilots helps.