I have a Sig M400 and I'm having a problem with short stroking. I've run a variety of factory ammo through my M400; 55, 62, 64 and 69 grain from Hornady, Winchester and other reputable companies. 500 to 600 rounds and no problem. I've started to do my own reloading. The following are .223 loads not 5.56 loads. Sierra 65 gr SBT with 23.9 grains of IMR4895, no cycling problems. Barnes 62 gr TSX with 23.9 gr Varget, no problems. Sierra 69 gr HPBT with 23.7 gr IMR 4895, no problems. My problem is in using the Sierra 69 gr HPBT with 19.7 grains of IMR 4198. i.e. 1. Firing with one round in the clip the bolt does not travel back far enough to lock in place, most of the time. And 2. Firing with multiple rounds in the clip the bolt travels back far enough to pick up the next round but the round does not seat itself correctly on the bolt face and as a result the cartridge jams in the receiver. As an added note this problem is intermittent. I can fire two, three or sometimes four rounds before I get a jam. I suspect that the pressure envelope (duration) of the IMR 4198 is not long enough to force the bolt to retract completely. The question I have is; do I increase the powder load (from 19.7 to 20.0) which will increase the pressure spike but reduce the pressure duration or decrease the powder load (from 19.7 to 19.4) which will reduce the pressure spike but increase the pressure duration ? Any help will be appreciated.