I'm confused, you are saying 20" barrel but showing 26" barrels for some of the velocities and I did not see a 3250 fps 75 Amax load.
Yes those are from quickload but that is what Mike sent and where he is firmly stating that's his max loads he recommends. Like I said cousin tried more and loosened up primer pockets.
But the gun shoots everything great, it is an accurate round and is better with the heavier bullets. Cousin almost sold his due to the trouble it took to get less than his 223AI with 50 gr bullets (his favorite bullet weight) but tried the 60 gr NBT's (I thought it was Vmax's) and now loves the round. He switched to Imperial sizing lube and uses a 243WSSM die before going on down to 22 caliber.
He had a 223 WSSM that could've been the king but got less than 1000 rounds before toasting the barrel. Tried the 25 WSSM but saw the 22 PDK and it's reported 3900 fps with 50 gr bullets but the guy quit building them so he tried Mikes version. Long story short, he has 3 or 4 223AI's and for him they make the most sense.
I will remind him of the new powders and look forward to seeing your results.
