Case Length Variance

[Movie Man]

Question about case length, and C.O.A.L. measurements.

I understand a bit about the coal being N overall lebgth and how yhat might change depending on the design of the bullet.

However why do different reloading manuals give differwnt case or brass lengths to trim to. Shouldnt this be standardized and the same for .270 reloading sierra as to barnes .270 reloads? Why would there be differences here.

Read More

 

[DizzyJ]

Question about case length, and C.O.A.L. measurements.

I understand a bit about the coal being N overall lebgth and how yhat might change depending on the design of the bullet.

However why do different reloading manuals give differwnt case or brass lengths to trim to. Shouldnt this be standardized and the same for .270 reloading sierra as to barnes .270 reloads? Why would there be differences here.

Got examples of two different manuals giving different trim lengths?

 

[Movie Man]

Yes

 

[Movie Man]

Yes, reason for the question.....

Barnes states case trim length to be 2.530
Nosler shows case trim length to be 2.540

I know it's only a small amount but would expect that number to be a don't exceed length and the same for all companies.

 

[Koda]

Barnes states case trim length to be 2.530
Nosler shows case trim length to be 2.540

Nosler is just being lazy and assuming you know the saami tolerance. Barnes is assuming you want to trim to the middle of the tolerance.
This is what happens when engineers use unilateral tolerancing but at least in this case its applied correctly, it simply means the nominal dimension is to be strived for without going over. Simplified, its better for the case to be longer than shorter. Nosler for the win.

 

[Movie Man]

Nosler is just being lazy and assuming you know the saami tolerance. Barnes is assuming you want to trim to the middle of the tolerance.
This is what happens when engineers use unilateral tolerancing but at least in this case its applied correctly, it simply means the nominal dimension is to be strived for without going over. Simplified, its better for the case to be longer than shorter. Nosler for the win.

Thanks Koda,
I'll have to go look up the saami tolerances. So long is bad sorter is good.

 

[Certaindeaf]

Question about case length, and C.O.A.L. measurements.

I understand a bit about the coal being N overall lebgth and how yhat might change depending on the design of the bullet.

However why do different reloading manuals give differwnt case or brass lengths to trim to. Shouldnt this be standardized and the same for .270 reloading sierra as to barnes .270 reloads? Why would there be differences here.

Probably because it doesn't matter.

 

[orygun]

Probably because it doesn't matter.

The number itself doesn't really matter, but keeping all cases a uniform length does. More so in a cartridge that receives a crimp.
I've always been kind of surprised that not all loading manuals provide a "trim to" length.

 

[Mikej]

Simplified, its better for the case to be longer than shorter.

Why? Unless you are concerned about .005"+/- case length difference? Or the neck tension?

I only use two books, The Speer 14 and Lyman 50th. Speer is 3.539"-2.549". And Lyman is a "Trim To" of 2.540". I read any source, with only one case length, as a TRIM TO length, and maximum case length would be .010" more. For my type of shooting, casual, 100 yards, just havin' fun kind of shooting, a couple/three thousandths doesn't matter to me as long as it within that ten thousandths range. (roll crimped cases accurate trim length means more) You mentioned above that you're getting pretty anal about getting one hole groups at REAL distance? I would suggest that getting that anal over a couple of thou on your case trim is something you don't need to worry about, if at all, until you have done everything else to get accuracy first.

 

[Mikej]

I've always been kind of surprised that not all loading manuals provide a "trim to" length.

I haven't looked at bunch of different manuals but I presume manuals with only one trim length mean "Trim To", and you have a ten thou above that upper limit.

 

[Koda]

but I presume manuals with only one trim length mean "Trim To", and you have a ten thou above that upper limit.

that is incorrect, the "trim to" length is a max length....

 

[Koda]

So long is bad sorter is good.

to clarify, its the opposite. Longer is better, shorter is bad.
anywhere inside the saami tolerance is fine but longer is better to maximize case life.

SAAMI Standards - SAAMI

Note: New & Revised Cartridge & Chamber Drawings not yet included in the standards can be found HERE. American National Standards Published by SAAMI The SAAMI Standards are published to provide safety, reliability, and interchangeability standards for commercial manufactures of firearms...

saami.org

 

[Mikej]

that is incorrect, the "trim to" length is a max length....

Not according to the Speer manual. They have Trim to and Max length.

 

[Mikej]

but longer is better to maximize case life.

I've rolled his around in my mind. I don't see how trimming would shorten case life? Your not working the brass, like when sizing. And you're not heating the brass. Trimming to trim-to length would mean you don't need to trim as often.

 

[Koda]

Not according to the Speer manual. They have Trim to and Max length.

My bad, Im not familiar with Speer manuals. You said they only have one trim to length but it looks like they also cite a max trim length so I was confused as I thought it was referring to the max trim length. Its the max trim length that once cannot exceed by .010 or any amount.

 

[Koda]

I've rolled his around in my mind. I don't see how trimming would shorten case life? Your not working the brass, like when sizing. And you're not heating the brass. Trimming to trim-to length would mean you don't need to trim as often.

If you take a piece of metal and remove some of its material you make it weaker. If you trim more than needed then you will get one or two less firings out of the case at the end of its lifecycle. This is why saami uses a unilateral max tolerance rather than a symmetrical tolerance. I get that reloading manuals are cherished, but this is why I only use saami specs for case prep.

 

[Mikej]

You said they only have one trim to length but it looks like they also cite a max trim length so I was confused as I thought it was referring to the max trim length.

The Lyman manual has only "Trim-to" length. No max length. I've taken that to mean a source citing only "Trim-To length that I would still be in spec up to .010" over Trim-To.

 

[Mikej]

If you take a piece of metal and remove some of its material you make it weaker. If you trim more than needed then you will get one or two less firings out of the case at the end of its lifecycle. This is why saami uses a unilateral max tolerance rather than a symmetrical tolerance. I get that reloading manuals are cherished, but this is why I only use saami specs for case prep.

But brass grows when you shoot it. If you only trim to max length it may grow to need trimming with the next firing.

 

[Koda]

The Lyman manual has only "Trim-to" length. No max length. I've taken that to mean a source citing only "Trim-To length that I would still be in spec up to .010" over Trim-To.

that I will have to disagree with if their "trim to" length is equal to saami spec max length.

Again, this is why I only use saami specs. Reloading manuals are influenced by their authors bias and personal preferences.

 

[Koda]

But brass grows when you shoot it. If you only trim to max length it may grow to need trimming with the next firing.

true,
rethinking my position on this you may have a point here as long as you stay within the saami tolerance it probably doesnt matter or affect case life. I was just thinking that if the case is kept farther back then by removing more material it weakens the case faster but now Im not certain. Appreciate your input here.

their might still be an advantage to trimming less for more neck tension.