Colt 6940 split case necks

I have a colt 6940 that is bout 6 month old. Just got done shooting a total round count of 200 round thru it. While I was policing up the brass, I notice that the case necks all showed signs of burn thru and spliting in one location.

The rifle is accurate enough, bout 2 inchs at 50 yards with irons. The ammo I am using is some old American Eagle .223 55grn FMJ stuff. Case head stamp is LC01.

I know its not normal, do I have a bad chamber? I shot the same stuff out of a Rugar SR556 and SCAR 16 and they didn’t show the same issue.

A photo or two of the empty brass might be helpful.

I knew I should have keep some of the damaged brass…