When To Trim Cases??

[roysclockgun]

Maybe I am trimming before a need to do so.
30-06 for instance: The reloading manual shows new brass at 2.494" and to trim to 2.484". I have been trimming anything longer than 2.494"!
What is the max stretch that I can allow, before trimming?
Best to all,
Steven L. Ashe

 

[DrMike]

Steven,

Normally, cases should be trimmed when they are 0.010 inches over SAAMI specs. This depends on the cut of your chamber, of course.

 

[Charlie-NY]

Maybe I am trimming before a need to do so.
30-06 for instance: The reloading manual shows new brass at 2.494" and to trim to 2.484". I have been trimming anything longer than 2.494"!
What is the max stretch that I can allow, before trimming?
Best to all,
Steven L. Ashe

I've never seen "new brass length" listed in a reloading manual. New brass is typically much shorter that "max length". Hornady manuals list the "max length" and the "trim to length" which is typically .010" less than max.

 

[roysclockgun]

Okay, thanks for that.
However, I am loading light loads just for range testing older military rifles. US M1 Rifle, US M1903 and US M1917, in which chamber dimensions are generous. Am I going into dangerous territory by going over the max. case length shown, in these tests? Again, for 30-06 the max shown is 2.494". I want to use cases measuring up to 2.504" in these test, using 150gr. fmj bullets and 49gr. of milsurp IMR4350.

 

[DrMike]

The primary danger arises when the case neck expands into the chamber neck and is restricted so as to generate excessive pressure. Though you are using light loads, I'd tend to err on the side of caution and trim whenever the cases exceeded 2.494 inches.

 

[Guy Miner]

Dr. Mike - I remember learning that lesson in the 1970's when I didn't have a case trimmer!

I loaded up my favorite 6mm varmint loads without trimming the brass and was surprised when I had all kinds of pressure problems...

Young fellow. Hot rod cartridge. Lots of IMR 4350... Wish I'd had a chronograph, I'll bet velocity was sizzling!

Had to really lean on the bolt to get it open... Pulled the bullets, got a trimmer and started over.

Guy

 

[DrMike]

I'll wager that we've all done that, Guy. Usually, it is just enough pressure to be a good lesson. Occasionally, it is more than a good lesson.

 

[Elkman]

When my cases get near the max length I trim back to the listed trim length, on most of my rifles thats after about three or four loadings.

 

[Silent Sam]

I full length resize new brass and trim to minimum as part of case prep every time for load work up and hunting rounds. I don't ever have to worry about brass that's too long and don't fool around measuring each piece.

 

[300WSM]

It varies. There is no set dimension for each and every gun alike as a go/no-go type of number.

I've always found that if you start with a trimmed case, you can get three firings before a trim is needed.

Sometimes that third firing can be a little snug but still good.

Then trim back .010 below SAMMI and repeat process.

 

[runtohunt]

Interesting subject. I have always trimmed after each firing. A fellow at the range told me that I am trimming way too much. My thought was that if I didn't trim after every firing, I would get increased pressure from the first batch of trimmed cartridges to the last batch of cartridges that would be 0.010 longer and that, that increase in pressure would change POI. Am I being silly?

 

[DrMike]

Interesting subject. I have always trimmed after each firing. A fellow at the range told me that I am trimming way too much. My thought was that if I didn't trim after every firing, I would get increased pressure from the first batch of trimmed cartridges to the last batch of cartridges that would be 0.010 longer and that, that increase in pressure would change POI. Am I being silly?

I would say you are being cautious, rather than silly. It doesn't hurt a thing to trim that frequently. One advantage might be that you start from a consistent cartridge length with each loading.

 

[joelkdouglas]

Interesting subject. I have always trimmed after each firing. A fellow at the range told me that I am trimming way too much. My thought was that if I didn't trim after every firing, I would get increased pressure from the first batch of trimmed cartridges to the last batch of cartridges that would be 0.010 longer and that, that increase in pressure would change POI. Am I being silly?

I would say you are being cautious, rather than silly. It doesn't hurt a thing to trim that frequently. One advantage might be that you start from a consistent cartridge length with each loading.

I end up trimming pretty much every firing also--sometimes I can skip a firing. I measure a sample of 7 or 8 cases, and if any of them are over 2.494 (30-06), or SAAMI length, I trim all the cases.

I also very slightly full size each firing, which more than likely causes the trimming.

 

[300WSM]

Interesting subject. I have always trimmed after each firing. A fellow at the range told me that I am trimming way too much. My thought was that if I didn't trim after every firing, I would get increased pressure from the first batch of trimmed cartridges to the last batch of cartridges that would be 0.010 longer and that, that increase in pressure would change POI. Am I being silly?

What are you shooting? A typical sporter/hunting platform? If so then trimming is overkill. For example starting with all cases trimmed, sure you might re-size ten of them and get a variation of .001 or so...but you wont get much more than that, trust me when i tell ya that your typical sporter/hunting rifle will not distort accuracy one bit from such a little variation on the case length.

Even a 1000 yard bench gun some shooters will shoot the same case before trimming more than once....these guys are as overkill as they come.

 

[.300winmag]

I trim my cases after every firing. It goes quickly and it makes me feel better in the fact that the surface area contacting the bullet should be more consistent. Overkill, probably, but it is how I do it.

 

[Elkman]

Overkill, probably, but it is how I do it.

I think you are right !!!

 

[DaveA37]

Interesting topic indeed but to trim or not to trim, Hmmmmm?
Most of us are concerened about the cases expanding too much.

What happenes if the cases are trimmed TOO SHORT, Say .003-.005 BELOW the specified case length? Certainly there would be some significant expansion once the cartridge is fired.

 

[DrMike]

What happenes if the cases are trimmed TOO SHORT, Say .003-.005 BELOW the specified case length?

No problem. There is a point at which the neck will no longer hold the bullet, but even up to 0.005 below standards does not constitute a danger. Aesthetically, it is quite unsatisfying, however.