Results of AR15 case life test using LC Brass

J

jepp2

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CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

Over the past 2 years I have been running a test to determine the case life for LC brass fired in Ar15 rifles. I wanted to know when and how the cases would fail.

This isn't an endorsement to load brass beyond what you normally do. It was for my benefit, but I wanted to share the results.

Bottom line, 19 of the 20 cases involved in the test failed due to cracks/splits developing in the root of the gouges created when the fired case was being extracted and contacted the locking lugs on the barrel extension.

My case life results for the 20 cases involved in the test:
  • 25'th firing 2 cases failed (1 due to a small crack at the junction of the body/shoulder),
  • 26'th firing 4 cases failed,
  • 27'th firing 4 cases failed,
  • 30'th firing 6 cases failed
  • 32'nd firing 2 cases failed
  • 36'th firing 1 case failed
  • 37'th firing 1 case failed

I was using once fired brass picked up at the range. My load was 26.0 gr of WC 844 with a 55 gr. FMJ bullet providing a velocity of 3050 fps in a 18" barrel. QL predicts the peak pressure would run about 53K PSI.

None of the brass showed any signs of primer pocket enlargement, none of the brass had any thinning above the head (indicating potential case head separation).

I set the shoulder back ~0.003" each sizing. I annealed case necks each 5'th firing.

I took pictures of the case necks as they failed. As I saw the trend of what was causing the failure, I made minor modifications to my AR15's which has eliminated 95% of the gouges. I am including pictures of the gouges where the failures occurred (what doesn't look like much to the naked eye looks pretty dramatic when magnified) and the sharp corner on a typical barrel extension that caused the gouges.

[URL=http://s860.photobucket.com/user/jepp2/media/Typical%20Gouges_zpseuuifetm.jpg.html][/URL]

[URL=http://s860.photobucket.com/user/jepp2/media/Barrel%20Extension%20Locking%20Lugs_zpsfye99o6n.jpg.html][/URL]
 
Thanks for sharing you results. Always wondered about actual case life. Theres alot of fluff thrown around about it. Nice to see an actual test.
 
Interesting how well that lasted. Thanks for the test effort.

jepp2 said:
My load was 26.0 gr of WC 844
Click to expand...

If it's surplus WC 844 and not H335 (canister grade WC 844), the burn rate may be further away than H335 is controlled to (max load 25.2 grains with this bullet weight from Hodgdon). So QuickLOAD may not match its peak pressure well.

Since it's over the equivalent published load, I put the required warning into your post for you.
 
In don't anneal, and I get 5 - 8 reloads I would guess before neck splits occur. Given that the brass I get is mostly free but decent quality range brass (same brands and headstamps from same session), or if using brass from my large quantity of new bulk LC or commercial brass acquired years ago, what I do is economical enough for me.

These are very interesting test results and thanks for sharing them.
 
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That is interesting. Makes the conventional wisdom of "4 reloads and chuck it" seem very conservative.

Jimro
 
Great photos, info ty.

Brand of dies used? Brass life has always been cut short for me using an old RCBS FL die. The necks fail. Trying a new RCBS now. Over working the neck area seems to be the main problem. Bushing dies would be better.
 
My bad for not putting the load disclaimer in the post, thanks Unclenick!

I used a standard FL Redding resizing die with a carbide expander. I do lube the outside and inside of the case necks.

As I mentioned, I was only setting the shoulder back 0.003" per firing.

The neck OD after firing was 0.254" and after sizing and expanding was 0.244", so it was seeing 0.010" expansion. My die only undersizes the neck about 0.001". That is why I did anneal every 5'th cycle. But clearly the amount of expansion during firing was too much for the thin brass in the root of the gouges and thus the failures. As soon as I could see any light through the case neck, I retired it. Some were barely visible.
 
Exactly what did you relive from your barrel extension?
Click to expand...

To eliminate the gouges I shorted the ejector spring about 2.5 coils to reduce the force it put on the ejecting case into the locking lugs, and I broke the sharp corner of the 2 locking lugs that were causing the gouges.
 
Thanks for sharing. Good test data is rare.

FWIW, I do that mod to all of my ARs, knocking off the sharp edges of the barrel extensions, but I leave the ejector and extractor and full power.
 
Very helpful.

Just wanted to note that is a very small sample size out of single population.

I have always felt comfortable with ten and then pitch.
 
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