How much does brass length really affect things

So - in my ongoing battle to figure out why I suddenly have unreliable 45 reloads it was suggested that the crimp was incorrect on some rounds due to the brass 'shrinking' with repeated re-use. On the face of it this seemed possible as some of the 45 brass I have is at least a decade old. So I decided on some measurements.

Starline (for want of a better baseline) advertise their new brass as being between .892 and .897
I have some once fired (as in - the cases are from rounds that I fired that were factory new) starline brass and a sample of 10 cases shows that they are between .886 and .889
Digging through the tub of cleaned, random, 45 brass I see measurements anywhere between .887 and .869 (so - a maximum of <3/100s of an inch shorter than new)

Using the shortest ones I found I dry loaded a couple (I'm assuming here that the lack of primer and powder are not relevant at this level of accuracy) and got a crimp of .463
I took a .889 case - same load - same crimp.

This leads me to think that brass length is effectively irrelevant in 45ACP and isn't contributing to the functioning woes.

Anyone got any thoughts and comments?

Derek

straybrit wrote: I suddenly have unreliable 45 reloads 

Derek

Derek,

Please explain unreliable;
Failing to chamber?
Failing to fire?
Wider dispersion on target?
other?

The issue with brass reloaded many times that, others have stated as a concern in obtaining reliable accuracy, was the loss off consistent crimp pressure due to over worked cases.

Ian

Essentially I get very variable impulse - in some cases resulting in failure to eject. I've had an ongoing issue with the powder (see the WST threads) and I've looked very hard at the reloader (see thread on cleaning the powder feed) but these aren't proving to be a complete solution.  This is kinda interesting in as much as I had effectively zero issues prior to my 18 month medical layoff (and the remaining rounds from that era performed as expected) so I'm trying to nail down what's changed.

REConley's post above brings something to mind that I hadn't considered - that is that the strength of the material is not a constant over time/use - so even though the crimp might be the same it might not be achieving the same results.

I'm going to retry by loading some of those once-fired cases and see if I see the same variability

It's all a learning experience.

Derek.

A couple of concepts regarding brass mechanical properties.  

First, there is no time-based change in properties of cartridge brass at the temperatures we use brass cases.  Once the brass is formed (crimped) the amount of tension residual in the brass does not change.  This is not true, however, for the lead bullet.  Lead will “creep” and change shape at room temperature while under relatively low stress.  It may seem glacial in its response but within a few years the lead no longer has the same stress or shape.  Note that the time frame is months to years.  

It is my guess that there is a mechanical issue here.  Either in the chamber or cartridge.  I suggest that you use a sharpie marker on the whole cartridge and place it in the chamber, then close the slide.  You can remove the extractor before you do this.  Then use a rod to push the round out of the gun.  What is causing the issue will be apparent.

I am still reloading 1971 brass. It isn't the only brass I have but I have a bunch of it. I can't tell any difference between it and new Starline for reliability. If you hadn't mentioned that your older brass was working fine and the new stuff wasn't I would think Wobbley nailed it but it is doing the opposite. It also cancels out my theory that it was the 18 month layoff that was the problem. It is easy to limp wrist a .45 if things hurt. I suppose it could be dampness or some chemical reaction weakening your powder. Just spitballing here. I am sure you will figure it out.

Len