When trimming-

[Ponder_MD]

I did search the archives for this but didn't quite find the answer I was looking for.

When trimming brass, do you trim for the shortest tolerance or the longest? Why?
Example: A .30-06 Springfiled case should measure between 2.494 and 2.474. Do you aim for 2.474, somewhere in the middle? The max of 2.494?

Also, here's a minor headscratcher for me- I have some once-fired, deprimed, cleaned, resized .30-06. I have not yet trimmed them. So far, they are all measuring around 2.48X. Do I still need to trim them?

 

[Growler215]

You don't gotta trim until its over max.

I trim to min, and then not again until near max as long as all rounds are the same load and not roll crimping. This minimizes the amount of time spent trimming.

 

[Ponder_MD]

You don't gotta trim until its over max.

I trim to min, and then not again until near max as long as all rounds are the same load and not roll crimping. This minimizes the amount of time spent trimming.

Ah, so you don't have to trim "every time" as long as it's in spec. Thanks.

 

[guzma393]

I did search the archives for this but didn't quite find the answer I was looking for.

When trimming brass, do you trim for the shortest tolerance or the longest? Why?
Example: A .30-06 Springfiled case should measure between 2.494 and 2.474. Do you aim for 2.474, somewhere in the middle? The max of 2.494?

Also, here's a minor headscratcher for me- I have some once-fired, deprimed, cleaned, resized .30-06. I have not yet trimmed them. So far, they are all measuring around 2.48X. Do I still need to trim them?

For plinker brass that just calls for "just needs to be in saami spec" I trim on the short end since the brass will eventually wear out or the necks will split before it has to be trimmed again, which is about 4-5 firings. I.e. I trim 223 at 1.745, where recommended trim length is 1.75". I leave .005" tolerance since I am trimming these along a press mounted power trimmer.

For low volume purposes, I trim on the saami spec recommended trim length and make everything uniform.

Sent from my SM-A136U1 using Tapatalk

 

[Growler215]

Ah, so you don't have to trim "every time" as long as it's in spec. Thanks.

Unless you're roll crimping. For that it's easier to trim to the same length every time than to readjust the roll crimp/seating die every time.

 

[Ponder_MD]

Cool, thank you gentlemen. If I get 4 firings out of my brass, that's plenty for me.

 

[K31]

It depends.

If you are trying to adjust your OAL so you are a few thousands short of the rifling, then you might need more than the minimum case length to hold your bullet firmly.

 

[BFMIN]

Its also going to vary slightly depending on your press!
I use a Dillon RL 550b, with that you trim to length BEFORE resizing! Because of that I trimmed & resized a handful of scrap brass. I normally would trim to minimum, when the fired case reaches maximun, but after measuring the length before & after resizing I determined the stretch average 5 thou. Now I trim to min minus 5 thou. That way they reach min on the first resizing.

 

[Harrys]

I trim to fit my chamber.

 

[E.Shell]

You don't gotta trim until its over max.

Exactly.

Your long measurement is "maximum". Any longer risks hitting the end of the chamber neck, If a too-long case neck hits the end of the chamber neck, the camming action of closing the bolt can create a crimp where none belongs. This can raise pressures, often drastically.

Your short measurement is the recommended "trim to" length and is usually about 0.010" shorter than maximum.

If not crimping, there is no need to be exactly the same length, as long as all are below maximum.

Harry says above that he trims to fit his chamber, and yes, some chambers exceed SAAMI dimensions so there is not need to stay below published maximum if you know your actual chamber length. Otherwise, staying below SAAMI maximum should keep one out of trouble.

I trim to min, and then not again until near max as long as all rounds are the same load and not roll crimping. This minimizes the amount of time spent trimming.

Yep. If crimping, especially with a roll crimp (normally engaging a cannelure) or sharp taper crimp, the length of all cases must be the same. Length variations = crimp variations = pressure variations and often variations in accuracy.

The 0.010" difference one typically sees between 'trim to' length and maximum length is designed to provide several firings between trims. If you are stretching cases so badly that you have to trim more often, revisiting your full-length die setting is necessary. Know that all your die manufacturer cares about (in his F/L die setup instructions) is whether the round will chamber, they don't give a sh*t about your case life.

Shooting near max loads is often necessary to get into the upper OCW node, which is where we must be for long range precision. This can be hard on brass.

Match brass is really valuable, not only because it's usually premium brass, but also the hand work that goes into match brass, like truing primer pockets, reaming flash holes, deburring the inside of the flash hole, neck turning and VLD chamfering. We shoulder bump our brass during sizing to allow 0.002" shoulder clearance, so this is the amount of growth we WILL get at each firing.

This means that if I trim to my -0.010" recommended 'trim to' length and use either a bushing die or a lubed expander in a standard F/L die, I will get 4 to 5 firings before trimming is necessary again.

BTW: The kicker is that all this brass you are trimming off is ultimately coming from the web of your case, taking you step by step toward a case head separation...

 

[erwos]

The real mindscrew is when you find out certain companies produce brass that is actually significantly below trim length from factory. Looing at you, Federal.

 

[floatingboy]

I don't think I saw anyone say it, so don't measure until after you size it (if you are full length sizing).

 

[Ponder_MD]

@E.Shell Lots of great information in your reply. Many thanks.
@floatingboy Right. My understanding is because the sizing process smooshes the brass longer. It has to flow somewhere.

I am not planning on crimping my brass this time around. I'm still unclear- under what circumstances is crimping desirable?

 

[floatingboy]

Yep!

 

[E.Shell]

I am not planning on crimping my brass this time around. I'm still unclear- under what circumstances is crimping desirable?

Rifle cartridges? Almost never. Ammo for semi-autos is often crimped, but the bullets must have a cannelure.

Pistol cartridges? Almost always. At least a light taper crimp is usually applied for most semi-auto ammo, and revolver cartridges, especially magnums, are usually roll crimped.

 

[wilcam47]

I trim under max. But i dont have a lot experience. We tested 308 rounds fired 3 times and it didnt change or stretch. My thoughts is if you trim to minimum you dont have much left. But again i dont have a ton experience.

 

[Ponder_MD]

Rifle cartridges? Almost never. Ammo for semi-autos is often crimped, but the bullets must have a cannelure.

Pistol cartridges? Almost always. At least a light taper crimp is usually applied for most semi-auto ammo, and revolver cartridges, especially magnums, are usually roll crimped.

Sorry, I should have provided more context. I meant for semi-auto rifle ammo.
In this instance, can you not crimp? What are the consequences if you don't?
Can you just do a light crimp or does it have to be a roll crimp?

I roger on the cannelure.

 

[slsc98]

Geez, MDS being what it is these days, I saw this thread title and opened this thread expecting something else (before I noticed we’re in the Reloading section