Here's a couple slow powder references. 6" G20 conversion barrel throated to allow max oal of 10mm mag. Do not reduce oal!!! .426 case head expansion on 2400 load .425 on 300mp 158gr berrys php, 11.5gr Alliant 2400 @ 1.270" = 1479fps 158gr berrys php, 14.0gr Alliant 300mp @ 1.270" = 1357fps 300mp load makes a huge fireball!!!