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223 case neck separation


kmca

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Had 2 cases separate at the neck yesterday.  It seems the first fired and the case neck separates and sticks in the chamber.  Second round gets the neck of the previous round stuck and the rifle won't go into battery and is manually ejected.  I've shot a few thousand rounds through this rifle and it never happened before.  I'm using once fired Federal brass, W748 powder, RCBS small base die for sizing, the rest are Dillon. Headspace in the rifle is okay.  Any ideas why this is happening?

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First things first. Make sure your chamber is free of any kind of obstruction from the previous case. Fire a factory loaded round and check the case for any kind of abnormal markings that might indicate a problem.

At this point I can just give you little things to check.

The small bass die works the brass a bit more than standard full length dies as it sizes to minimum sammi specs as well as a bit further down the case body to help with reliably in autoloaders and when processing military brass that had been fired in guns with very generous chambers. IMO unless you have a particularly tight chamber to where a standard full length size die won't cut I'd avoid the small base die just cause it works the brass so much more.
Make sure the expander ball on your decapping rod assembly is properly squared away and not tweaked to one side.
Make sure brass is trimmed to 1.750".
If you must crimp, seat and crimp in separate steps.
Consider using a body die to bump the shoulder back and then a neck sizing die on the neck.
Annealing works nicely for necks as well.




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Thank you for your reply.

Barrel is clear of obstruction.  Since it happened in the first 25 rounds, then again in the last 25 rounds after a 100 round day I don't think that would be a problem.

I have fired factory ammunition and there don't appear to be any differences from my reloads.

Since I use the reloads in several different AR's, I was trying to make the reloads "universal".  The rifle I use most, doesn't want to chamber my reloads without using the small base die.

Brass is first deprimed, cleaned and trimmed to 1.750 then deburred and primer pocket cleaned.

The small base RCBS die says it sizes to a "little" undersized and bumps the shoulder back slightly.  Is that any different than the Hornady small base body die?  Is that what you're saying?

I thought about annealing, but the thought of doing every case make me want to use factory ammunition.

 

 

Edited by kmca
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A small base die is .002 to .003 smaller in diameter than a standard die and bumps the shoulder back .002 to .003 more than a standard die. So be careful when you use a small base die and "NOT" bump the shoulder back too far. The thumb rule for semi-autos is to bump the shoulder back .003 to .006. So be careful with excessive shoulder bump that can cause case head separations.

 

If there is a chance that you have some range pickup brass that was neck turned that may have caused the neck separation. If the neck is turned down too far into the shoulder area I have see cases separate at this point.

 

I buy a lot of bulk once fired Lake City 5.56 and 7.62 brass and use a small base die the first time I size the brass. There after I size my cases with a standard full length die.

 

NOTE, chambers and dies vary in diameter and length and nothing is written in stone. "BUT" a case fired in a semi-auto should be sized .003 to .005 smaller in diameter than its fired diameter. This insures the fired case will extract reliably and "spring back" from the chamber walls when fired.

 

 

Below I use a Hornady cartridge case headspace gauge to measure my fired cases from my AR15 and then bump the shoulder back .003.

 

H0SXHH8.jpg

 

Below the Wilson and Dillon case gauges do not check case diameter as you can see by how far the reversed case goes into these gauges.

The JP Enterprise gauge on the far right is made with a finish chamber reamer and checks case diameter.

I use the Hornady gauge to check headspace length and the JP Enterprise as the final "plop test" of the loaded rounds. (case diameter)

 

KSB3ZvP.jpg

Edited by bigedp51
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Neck separation can be caused by oversizing. A small "ring" of metal builds up at the shoulder, creating a stress line around the case. I'm sure a metallurgist can explain how the metal flows at a microscopic level...

 

I can feel the ring with a little bent paperclip run down the case wall. It's a PITA to do this, and I don't do it every loading. I spot check after the 4th loading of a batch of brass, then every other loading thereafter. That way I know when to toss the brass. 

 

I also quit using Federal brass for more than 2 reloads because it is so soft. 

 

YMMV

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You really need to post a picture.  Brass normally fails closer the the base, about 1/3 of the way up leaving much of the case in the chamber.  This is the portion of the case where the heavy base thins.  Sizing brass too much will do this as will excessive headspace.  Other potential culprits can be brass that's too long or burrs in the chamber.  

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Didn't find the case that separated, but here's the next round that pulled out the remainder of the case.bullet1.thumb.jpg.e3a752c83fb8821d0272170a97adee08.jpg

BTW, I'm using the Lyman case gauge and when I insert the case reversed, it looks like your JP gauge.

Edited by kmca
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