Starline 556 case head separation

[RabbitSlayer]

Pretty sure the reason this happened was you fired itin a 223 chamber then fired it in a 223ai chamber. And not jamming the bullet. So the brass grew in the body instead of getting shorter from the neck and shoulder like it is supposed to form from. Or do a false shoulder by running a 6mm expander into the neck then partial size it back to 223. This will leave a sort of donut to headspace the case hard back against the bolt face. Starline is just being nice and getting you more brass to replace it.

I always follow this rule. New barrel? New brass.

It is my understanding that the jammed bullet is used because a smith didn't set the barrel back, so you have no crush fit. The jammed bullets sort of acts as headspace. I also have come to believe that using 1x fired brass is very common for 223 ai, and is a major selling point for this chamber. Am I wrong? I'm not opposed to new brass or jamming bullets for fireforming. I didn't think I was doing anything wrong. I certainly read about jamming bullets and cream of wheat etc...

The case also got shorter on fireforming..I assume this means the brass came from the neck and shoulder not the body. I expected this to happen, so I purposely didn't trim the 1x fired brass. They were all over min, so I would have normally trimmed. I trim everytime, cuz I have no life...

 

[Oso]

Today’s challenge with 223AI is that manufacturers of 223 and 5.56 ammo are intentionally forming the cases shorter than spec in order to ensure reliable feed/extraction in any/every AR15. The shoulder are short/below spec location, which makes it difficult to get the crush fit that 223AI needs to fire-form cases. Based on some samples I measured variations in length from case base to the shoulder being as little as .005” short of spec to as much as .015” short. This translates to light strikes as fire pin just pushes these short cartridges further forward into the chamber.

Gunsmith will chamber of a 223AI one of 2 ways. Either they will cut it to 223AI spec and headspace as per Mr. Ackley original design OR they will set the barrel back further (shorten the chamber) to adjust for today’s “short” factory ammo.

My rifle’s chamber is set to the traditional 223AI length, which means that I can’t get a crush fit with vast majority of factory ammo. Only premium match ammo seems to hold to case specs and will work for my rifle. I just load my own to ensure case dimensions will allow for a crush fit.

 

[DShortt]

'Slight change in metallurgy making it harder at the base of the case'.

That sounds peculiar.

I'll be interested to see if I get a specific response from Starline or just a 'copy and paste' of this.

Just to update this, it took a while, but I did receive a reply from Starline.

"The only difference is, the 5.56 brass is a little harder in the case head area. (they receive a lower temp interdraw anneal)."

 

[socalal]

I have had the exact same thing happen when firing super hot varmint loads from an AR or a Mini-14. The loads shoot great out of my bolt action varmint rifle, but not out of a semi-auto. My theory is the semi-auto action releases so fast that the high pressure tears the brass in half, usually in the place where yours tore.