Thanks for the input.
On a whim, I tried 21.8gr of H4198, CCI450, LC brass, 55gr Hornady 55gr fmjbt, 2.2" col. But my chronograph had a stroke so no velocity from the 16" 1/8 barrel (unless ERR1 is a secret encoding of the velocity numbers). Seemed a fairly mild load that gassed enough to 3 o'clock my brass.
I know H4198 is less than ideal, but it is what I've got on hand.