I had the same problem with br4s. I called cci and they told me I was crushing the cup of the primer. I started trying to “feel” it seating properly instead of squeezing all the way down. Hand primer of course. Haven’t had a problem since
I have a 6.5 Creed AR WITH LESS THAN 100 rounds on it. I just never use it and am more into bolt guns.
Areo billet lower/Upper
MI key mod rail
Heavybuffers buffer and aftermarket buffer spring
24” criterion barrel with nice brake