Here were my results using a Competition Electronics Prochrono:
Weather: Sunny, calm winds and 42 degrees
Gun Information
Gun STI Custom
Barrel Schuemann 6"
Load Information
Powder Alliant E3
Primer Magtec Magnum
OAL 1.180"
Crimp .410"
Bullet Information
Weight 220 grains
Mfr. S&S Casting
Shape Tunicated- lead
P.Chg 3.0gr
Shot 1 753
Shot 2 767
Shot 3 755
Shot 4 782
Shot 5 749
Shot 6 745
Shot 7 760
Shot 8 810
Shot 9 755
Shot 10 786
High 810
Low 745
Average 766.00
Std. Dev 20
P. Factor 168.52
I need to work on better Std Deviation with more consistancy at the press. But looks to be about the same power factor with 3.0gr of powder with both Standard and Magnum primers. All rounds fired reliably and no pressure signs. I tested 40 rounds in 10 round lots at 3.0gr, 2.9gr, 2.8gr and 2.7gr loadings.