Case life, and sundry matters appertaining to performance:

[meles meles]

oomans:

We seek knowledge. Would you clever types be so kind as to outline the various factors that can influence the number of times a brass cartridge case can be re-used, the steps that are required to re-use it, and the effects that changes in cartridge condition can have upon performance. As examples:

1. A cartridge that is used several times stretches and eventually breaks.
2. Changes in case wall thickness influence the powder volume and pressure generated
3. Annealing is required as part of the reloading process

Why do we wish to know?

We're shortly to be setting out a "problem statement" that will be submitted to potential students at the Badgerkadamy who are seeking Master's and possibly even PhD level Materials Engineering problems to solve. If one of them likes the idea of the subject, and the issues involved in solving the materials problems behind it, then there will be some in-depth scientific research conducted into it...

[Dougan]

1 - Yes.
3 - Required?...No - but can get more life and better performance out of case that are going brittle after multiple firings.
2 - Being picky with the question - No it will not alter the powder volume, but could alter the air space volume - It's an interesting question though, and would be difficult to precisely calculate...The case loses mass when it's trimmed back to length, that can be measured, but the case does not 'thin' evenly...it's thicker at the head end, and gets progressively thinner towards the neck; so it would be very difficult to work out where/and by how much the cases were thinning and therefore how much it was affecting the inside volume...

...my best guess would be that even after multiple firings and multiple trimmings, the effect of case thinning on air space volume would be less than that of 1 thou difference in bullet seating depth...

...if you can work it out I'd be very interested in the answer...

[meles meles]

To work it out, my favourite little tree rat, we need to know what questions to pose...

[Dougan]

If you're posing a question specifically relating to reloading then - Assuming that the die returns the outside of the case to it's original size; then by how much does the thinning of the case reduce the inside volume?

But a better question for 'materials engineering' could be - Can a fired case be returned back to it's completely original dimensions? (that is without melting it down and starting again).

[meles meles]

Being pedantic, tree rodent, the thinning of the case will increase the internal case volume...

[Dougan]

Durrr!...been a long Monday...

Anyway...specifically, what sort of question did you have in mind?

[meles meles]

If we knew the questions, we wouldn't be asking...

Consider a few things.

A brand new case is used and after one firing it fireforms to the chamber it was fired in. It is now a tiny bit bigger. How much bigger ? How much has the brass flowed ? Where ? More at the shoulder ? More at the neck ? By how much has the brass been work hardened? Does it need annealing yet? Before re-sizing ? After re-sizing ? How much annealing does it need ? How long for ? At what temperature ? Full length re-size ? Neck size?

The once fired cartridge is now fired again. By how much has its performance changed ? Is it any bigger ? Thinner ? Longer ? Does it need annealing yet ?

The twice fired cartridge is now fired again...


Get the gist ? What questions do we need to ask ?

[Dougan]

I'll leave the answers about annealing to those who have experience of it.

As for the rest of it; I'm as curious as you...I've been doing a practical test with some 6.5 x 55 cases:

I started with PPU factory - after reloading them once (neck sized) I measured 25 of the cases; the shortest was 2.154" and the longest 2.161, and the average of them all being 2.157 - Then they were loaded (neck again) and fired again; with the shortest being 2.155 and the longest 2.163, and average 2.159 - the case had now become a bit of a 'crush fit' where they had expanded in the body and not returned much, so I full-lentgh sized them, and measured them again; with the shortest 2.162 and the longest 2.167, and average 2.164...

...I then trimmed them back to 2.155" (as recommended (wish I'd kept the shavings now to weigh)), and have fired 10 of them again so far, but not measured them yet...

...I intend to carry on measuring, noting sizing and trimming the same 25 cases until one of them shows signs that it doesn't want loading again...and hopefully that will answer some of the questions I had about how many times I can use the same cases in this rifle...


Btw: I haven't seen any signs that they 'need' annealing yet, and am not planning on doing so...but that's not to say that they wouldn't benefit from it...

[dromia]

While they are on they could also figure out why my 45ACP cases get shorter with firing.

[Dougan]

I wouldn't presume to try and answer a loading question that you can't Adam...

...but I did notice something about using a Lee Autodisk on my .357 cases - I don't know if I've set it up wrong, but when I powder the case, the belling action seems to shave a little brass off the edge of the neck (I know because I have to brush the small shavings off the shell-holder about every 100 rounds)...after more than 10 firings, the cases have hardly lengthened; and I can only assume that the action of the die is trimming them at the same rate they're lengthening...?

If that is the case, then they must be getting thin, but I've only had a couple of very small neck splits so far...