.45 ACP - surprizing case length variations.

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leonardj

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In spite of being told by numerous reloader/shooters that case length means little or nothing when it comes to accuracy with the .45 ACP, I decided to test a theory of mine over the past couple days.

I had often wondered why I would get occasional wild "flyers" that would ruin an otherwise respectable group. Not discounting that it could be "operator error", but did I move THAT much?

While reloading, I noticed that occasionally the crimp effort didn't seem to be the same on some of the cases. Could the amount of crimp (taper crimp) make enough of a difference to cause the wild flyers? How much variance could there be in the length of the cases?

According to the Hornady Reloading Manual, 6th edition - for .45 ACP:
Max case length: 0.898"
Case trim length: 0.893"

After measuring all my .45 ACP brass - about 2000 cases, all once fired, here is what I found: a variance of 0.064" from the shortest to the longest !!! The shortest case was 0.845"; the longest was 0.909" - 0.011" longer than the stated maximum case length.

The results were:
- only about 1% were longer than 0.091". (these will be trimmed to 0.090")
- about 90% were 0.080" to 0.090". (these are the cases I intend to use)
- about 5% were 0.070" to 0.079". (these cases, and all below will be discarded)
- about 3% were 0.060" to 0.069".
- about 1% were shorter than 0.059".

My take on this is that 10% of the reloaded rounds could have anything from an extreme crimp to no crimp at all. IMO, this has to affect the case pressures, resulting velocity, and obviously, POI. Does this seem logical? I am hoping that my next group of reloads, and targets, will make the tedious measuring of these cases worth while.
 
Very interesting. I do load "match" ammo. Meaning the most uniformly I can, but I did not measure the cases. I should measure some of them and will be interested in your results.
 
As an experiment why not reload all or some of the " 5%" the " 3%" and the "1%" groups separately and fire them for accuracy also. Don't change any of your reloading settings and load them up. If you don't document them also, you haven't proved they were the ones that caused the flyers. It would be interesting to know if the case length was that important.
 
Sounds like an interesting project. Would be very interesting to compare results between the out of spec brass and the carefully prepped and trimmed brass. I used to spend lots of time trimming, deburring flash holes and cleaning primer pockets. Didn't see all that much difference when I stopped doing that.
 
The more times it is fired, the shorter .45 ACP brass becomes. With the 200gr H & G seat the bullet so it just touches the rifling using same length (sorted) brass for max accuracy. This is not a good idea in IPSC or IDPA because of possible malfunctions, but works for bullseye where you have an 'alibi'.
 
Was there any relationship between case manufacturer and the length?

I know there are differences in case wall thickness. Remington brass (R-P and Rem-UMC) is noticeably thinner than other brands that I have. But I never thought to see if there was a difference in length based on brand. Of course, my brass is hardly once-fired, so I couldn't judge anyway!
 
EdGCNM said:
Was there any relationship between case manufacturer and the length?

I know there are differences in case wall thickness. Remington brass (R-P and Rem-UMC) is noticeably thinner than other brands that I have. But I never thought to see if there was a difference in length based on brand. Of course, my brass is hardly once-fired, so I couldn't judge anyway!
Click to expand...

The brass grows shorter in 45 ACP because of the large diameter in relation to the length. Full length sizing is not really full length because of the shell holder. Brass consistently loaded to major, power factor back in the day was 175 and you had to have some cushion, will expand at the base ahead of the extractor groove, where the sizer die cannot reach, the brass has to go somewhere so it flows into that area, shortening the overall length with time. Most 1911s actually headspace on the Extractor in practice, unless there is a tight match chamber, which was found to be unreliable in IPSC. The last thing you want in a match is a malfunction of any kind.
But I digress, don't worry about case length, use once fired brass, from YOUR gun, carefully inspected, for match ammo.
OPC X6
 
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