About your case life . I had an expirence with a mark X mauser in 22-250 . I was shooting up some Win 40 grn. 4000 fps factories . After about 8 or 9 I'm seeing gas leaks around the primers bright rings just above the heads stiff bolt . Down range all is as it should be ,3 in at 200 with 5 inside an inch . Repeat . Repeat . With new brass and some 55 grn fmjs turning around 3100 I had similar results . Checked case dim.s head growth all the normal ?????? No answers . Finally decided that the action/bbl was of such mass that it wasn't cooling and thus shooting "hot" powder . The factories and the handloads had head separation in brand new unfired Win brass starting at about the 6th rnd . The hand loads were middle of the road from Lyman . The 243 and 22-250 are close in a heavy action with a heavy bbl you could be seeing the same thing .