Question on why my 243 necks are cracking

Dultimatpredator

Well-known member
To give the history on the brass it was given to me. I don’t know how many times it was fired previously and how old it he brass is. I annealed all the brass about 2-3 firings ago. I am bumping the shoulders back approx 3000 th’s. They are all RP cases. I trim the necks every time back to minimum length as most have grown during firing. I have fired them in two different BCA 243 uppers. They have been sized each time in my small base RCBS sizer die. Is the brass getting worked that much after 2 to 3 firings that they are cracking already? It seemed after every firing I’ve been loosing around 3 to …or more, out of maybe 50 to 60 casings, to neck cracking. I would assume I need to anneal them again…maybe after every firing? I have shot 243 RP casings umpteen times my bolt actions and can’t recall have a cracked neck in any of them.

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I have the rest prepped ready to load. I’m wondering if I should anneal them before I prime and load? I always anneal before sizing the brass so it’s kinda backwards. Just wondering if it will save a few cases by doing so?
 
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I suspect the ARs basically have mil spec reamers for the chambers to ensure extraction. Mil spec is of looser tolerances so the weapon will continue firing under adverse conditions of dirt & combat grit getting into the chambers. The AR chamber necks are not tight benchrest necks and are letting the case necks expand more than your sporting bolt gun. The brass can't handle the stretching.

I had a similar problem years ago with a National Match .30-06 1903 Springfield that kept creating case head stretchings and partial separations. I took it to a gunsmith and he said the chamber was within SAAMI specs but .004 over exact so it would keep firing under less than ideal conditions: i.e. combat. He told me to not set the shoulders back as much and use a dedicated set of dies for that rifle and problem solved.

Your sizing die might need to be bored out a bit to prevent this over working of the case necks or just load up on brass and consider it the cost of using an AR.
 
My brass has a lot of deep scratches on the case necks. I wonder if the barrel lugs have burrs? I’ll have to see if I can lightly stone and polish the barrel lugs. I wonder if the deep scratches are making weak spots and causing the cracking?
 
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How hot is your load? I get neck cracks like this in all of my varmint rifles which are designed to shoot fast, like the 220 Swift or 17 Rem, after several loads have been through them. Annealing will definitely help but I don't expect to get more than 4, maybe 5 firings out of my varmint caliber brass.
 
Quote:To give the history on the brass it was given to me. I don’t know how many times it was fired previously and how old it he brass is.

If you can get some, I'd try shooting a few factory rounds, or known new cases (or even known once fired) and I'd bet you have no cracked necks. Old brass becomes brittle and are especially apt to crack when fired in "generous" chambers, as mentioned above. Unknown number of reloadings + older brass would be my guess.

Regards,
hm
 
QUOTE

How hot is your load? I get neck cracks like this in all of my varmint rifles which are designed to shoot fast, like the 220 Swift or 17 Rem, after several loads have been through them. Annealing will definitely help but I don't expect to get more than 4, maybe 5 firings out of my varmint caliber brass.
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I took a file and lightly went across all my barrel lugs. Then I polished them with a Dremel tool and mothers chrome polish. The scratches I was was getting on the case neck area is now very light on a few to non existent now on others. It went from light scratching to completely disappeared after shooting a few groups.
 
The 3rd,4th from the right don't look like they have even been sized/fired. Shoulder and neck not formed like the rest, What are the neck numbers? Especially neck wall thickness, old brass that has been neck turned will crack, sometimes when seating bullets. The cracks themselves seem to show a radial force, what are the fired neck diameter vs loaded diameter?
 
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with Wyobull …. Generous chamber. Mic a loaded, unfired round and then Mic a fired round before sizing. See how much your necks are expanding. Much more than .006-.007 and that brass is getting worked hard. A tight neck bolt action as a comparison often only has .002 or so.

Do similar checks on the should diameter and the case diameter just below the web.
 
I’m going to load some up with my regular size RCBS green box sizing die set and accuracy test to see it it tightens groups. I know the SB black box set opened up groups in my other 243 upper. I’ll have to see if the The regular sizer isn’t as hard on brass. I did find out I trimmed my brass a little to short. It was a 2.020”. Don’t know if trimming to short would have affected anything. I do know when I trimmed brass to 2.035” in my tightest grouping load combos it DID open up the groups. Must have been caused by more neck tension???
 
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