I just switched out a barrel on my 7mm rem mag. I'm also load testing for a 300 win mag. Using the same box (or boxes) of primers, CCI mags. I can once in a while hear a delay in the firing in the 7mm, snap/boom almost like a muzzleloader. Never had it happen in the 300 win mag. Re-checked my headspace and it ok. Could it be a issue with the firing pin?? Just cleaned that also. And the primers have a nice dent where the firing pin hits....