teach me about case trimming

[Sniperwannabee]

So reloading newbie here...I see the reloading books have a case length listed and i understand you need to trim it once it gets to that length but my question is: is there a tolerance you trim the case to so it has some time to grow again? to me if you trimmed it to the exact length you would have to trim after each firing. Is it common to trim it a certain length below?
thanks

 

[SupressYourself]

The Hornady manual lists a max length and a trim length. They are typically .01 apart. You want all cases to be the same length, but pretty much anything between those two works. Attached a screenshot of 6.5 Creed as an example.

 

[KnowNothing256]

Reloading manuals will list a max case length and a trim length. You trim to the trim length when it hits max length.

 

[Steel head]

I rarely have to trim brass
Maybe every 5-6th loading at most.
Dont run standard SH pressures and maul your brass in the dies and case growth is minimal in a bolt gun.
I trim it to whatever it was when new unless I know the chamber neck length and can let it get a bit longer without issues.

I make little case neck measuring gauges on lathe so I know exactly what I have.

 

[spife7980]

Saami spec gives a tolerance. Usually it’s a max length followed by a range below that’s acceptable.

“1.600-.020” which means with 1.580-1.600 being within the spec.

Most recommended trim lengths are right in the middle of that range, so 1.590

 

[Chickentoast]

I'll measure a few pieces of brass after each firing (that started the same length). To measure chamber, I'll fire them until the bolt won't close freely on a spent case (with firing pin out). Now I know approximately where the sweet spot lies, and when I'm getting close to chamber length. Quick and dirty for me is just measure 2 or 3X fired brass and trim to that size.

 

[Sniperwannabee]

Thanks for all the replies, I just wasn’t sure how accurate you have to be as my case trimmers are pretty cheap and don’t run to accurate or consistent. What’s would be the downside of trimming too much?

 

[Chickentoast]

Thanks for all the replies, I just wasn’t sure how accurate you have to be as my case trimmers are pretty cheap and don’t run to accurate or consistent. What’s would be the downside of trimming too much?

Less bullet in the case neck and inadvertent altering of the pressure curve (if it's a lot shorter) since projectile would exit the neck sooner.

 

[KnowNothing256]

Not too sure about the inconsistency, I see trims within 0.001” with my Frankford Arsenal Platinum multi-station. That’s plenty consistent.

 

[nutation]

Cases can be trimmed a little bit below the SAAMI minimum without problems. I've seen some surplus 5.56 ammo with cases about 0.010 below the minimum.

 

[lightman]

I have an old chart from Ohaus, old as in ancient, that list the max length and the suggested trim to length. Most of the trim to lengths are 10 thousands shorter than max.

All of the loading manuals that I have list case length numbers. Slightly shorter won't hurt anything but too long can cause pressure problems or difficulty in chambering the round.

 

[2aBaC̶a̶]

As with most things reloading consistency is the goal so I trim to make them all the same. I usually trim to kiss the shortest ones unless its stupid short.