Because I'm resizing 45 Colt brass now, I'll use these as an example. When I check fired, empty brass OAL I get 2.70". The body of the case, roughly around where the base of the bullet would be, is .478".

Now, after I run these cases (winchester) through my RCBS carbide sizer die, I get an OAL of 2.80" and the body measurement has shrunk to .470.

Now, what I'm wondering is, how much of this case length increase after sizing is from the body O.D. being reduced and manifesting in case OAL, or, how much, if any, of this is from the case stretching in the die?

Yeah, I have a lot of free time...

Why would a carbide die stretch brass? By pulling on it? I doubt the friction of the die is enough to "pull" brass longer when the case is pulled back out, especially since the case is sized smaller when pushed in.

Some handloaders believe pulling the neck of a rifle case over the expander ball stretches brass, but an experiment using the same die to size cases both with and without the expander ball found no difference.

Thats what I was always told about rifle cases. I bought a tapered carbide expander button for a 243 die, it didn't help.

Well if you squeeze the diameter back down that brass doesn't dissappear... it has to go somewhere.... it goes back to length. At least IMHO.

That's my take on it too. Squeeze down on a length of any round material, like dough, and it goes somewhere, like out the ends.

I don't like short brass, so I usually prefer to form cases from a larger version of the same cartridge, like 7mm-08 from .308 and .338-06 from .35 Whelen. Gives me some extra length to play with, trimming for an exact fit to my chamber. Of course you have to make sure that the neck doesn't end up too fat for the chamber, but I never experienced that.

I believe that more lengthening occurs from FL sizing than from dragging an expander back through the neck, but it's easy to test.

Paul

Yes.

I, too, have read about rifle brass stretching in the sizing die but often wondered if it could happen to a short, straight walled case like 45 Colt brass.

I guessed that the case was getting longer and shorter due to the bodies O.D. expanding and contracting.

My 45/70 brass does this too and it's not going through a carbide die of course, so I'm wondering if any of the sizing process is causing case stretch. I guess if I get a head separation I'll know more?

Yes.

Yes. Squeezing a straight wall case will lengthen things. Squeeze it, and material has to go some where. My 45-70 and 45-90 cartridges behave the same way. Shortest after being fired.

Typically pressures in straight wall cartridges are not sufficient to cause brass to flow. Now a Weatherby bottle neck cartridge is a different cat.

Are you sure your readings are correct? If I am reading your post right, your brass OAL is increasing 100 thousandths of an inch. I would highly question that.

I have seen little case stretch in straight wall handgun brass in 44 Rem Mag, 357 mag, and 38 +P.

If you had said 8-10 thousandths stretch...maybe...but 100 thousandths...I don't know.

Yeah, I meant my fired cases mic 2.070" BEFORE resizing and 2.080" AFTER resizing. I didn't have my dang glasses on before. I "get it" that the body of the case is expanding and contracting during the resizing process, but I wonder if any of that is from the die stretching the case.

It just occurred to me that if I fire the case again and it measures 2.070" again then I can assume that the die is NOT causing any case stretch...

Your carbide die is not stretching the case. If you doubt that, lube ten of them and run them through the sizer. The lube will reduce friction...see what happens.

You also said that if you fire the case and resize, and if it measures 2.070...you would rule out the die stretching the case.

IF that happens, the dies would have to be compressing the OAL. That is not going to happen on a straight wall case. Think about it.

Sizing lengthens cases. It's as simple as that.

I'd check your measurements again. An empty 45 colt case should be in the neighborhood of 1.285".

Ditto here. I use an RBCS carbide set for .357 & .38 and the Lee trimmer seldom if ever does more than skim the mouth after sizing. This is after hot LiL Gun .357 loads and mild Trail Boss .38s.

IMHO experience 45 (long) Colt chambers and throats as well as loading dies can vary a great deal. My only current one is a New Service Match Target from 1926 that is a great gun. I use a Lee 4 die set (also carbide) and since only one gun is involved, only size down to where I get good bullet retention (only shoot cast). As this revolver is an almost handmade gun, I have no chamber variance, so any case fired in any one fits every one.

I shoot moderate loads but with 300 gr bullets and have never had a problem with bullets sliding out, given a good roll crimp in the crimping groove.

Cases last forever. I'm still using some that I bought with my first New Service in 1963 !

Good shooting !

Fired case before sizing 1.270"



Case after sizing 1.280"



I really CAN read a caliper I just had a brain fart trying to run on my poor memory that's why I write everything down when I'm handloading.

That's better, the difference is .010" (ten thousands) versus what was stated in your opening post which was .100" (one hundred thousands). Write it down, check twice or three times, it's measuring same principle applies as in the old mantra "measure twice cut once". Otherwise you'll find that you've cut it twice and it's still short. Handloading and the measurements that go along with it can at times be baffling even for the experienced handloader.

270,

I'd be interested to know what is the diameter of your cylinders?

Take an diameter measurement of a couple sized cases. Fire them, and measure the diameter of the fired case.

The difference in that measurement is what is causing your OAL of your case to grow--not the carbide sizer "stretching" the case.

.010" still seems like of lot of case growth. I would venture that the diameter of your cylinders are on the up limit of spec.

Just for reference, and you probably know this. Max case length for 45 Colt is 1.285". Trim length is 1.275". I would not trim until the case length is 1.285"...and then, I would only trim to 1.275".