The case of 17HMR split neck cartridge cases and effect upon accuracy..........friend's rifle firing just perfect, I measured OD at shoulder/neck at .194 and .945 with no split necks. My own rifle, less than 500 rounds through it, suffers split necks and fractures extending through shoulder area (1 out of 5) with no dependable accuracy. Measurements all at .192, .1925......could it be a too tight chamber is causing this? r in s.

Easy fix, send it back to Cooper and they will fix it for free.