Went to the range with a dozen loaded 458 SOCOM (new Wilson Defense AR build kit-barrel, bolt & carrier). New Starline brass FL sized with Lee Die, CCI 350, RL7, Hornady 325 FTX. 5 of the 12 failed on first try, examined one and it looked like it had a very light firing pin ding. 2 of the 5 FTF fired on second try, other 3 would not and show no signs of firing pin strike. I have a Hornady headspace comparator, but not the correct bushing. I improvised with a 13mm deep socket to check relative headspace (yes this is sloppy) averaging 8 pieces of each (except 3 for FTF). With new Starline brass as 0, my FL sized brass was approx. -.0016, FTF pieces were +.0013, and fired brass was +.0108. This doesn't make sense as a headspace issue - could I have a bolt/firing pin problem?