I am "MOSTLY" breechseating them with a "plugged"(powder and wad) case since only about 0.125" of the base is in the case. And so 1.2" is in the bore.
beltfed/arnie

Their 420gr M4 Money bullet casts at 412-413 for me in 20-1. I use it for the longer distances and also had BACo make me one that casts at 426gr and is 1.512" long. First time out The 426gr bullets seems to shoot better at 600yd. But, I'm shooting a 14.5" twist barrel. 

Was shooting the Saeco 640 bullet (370gr) at 200yd. It would hold the 10-ring of an SR-1 target, but just barely and my scores were in 97-99 range with a few Xs. Tested it against the BACo 400gr Kidwell bullet and the groups went from ~2moa with the Saeco down to ~1moa for the BACo. The 400gr bullet will hold the x-ring when I do my part (generally shoot 100-5x+ score). 

Deadeye Bly switched from shooting the Saeco 640 at 200yd to a Brooks 420gr bullet at the most recent match we shot. Think he may have shot a new personal best of 100-5X at the match with the heavier bullet and believe his Shiloh has a 16" twist barrel. It shoots the 420gr bullet well all the way out to 600yd, so there is no reason not to try the 420gr BACo.