Follow the gunmaker's recommendation. 777 gives more velocity (and pressure) than black. I hope you're loading that by volume!
100gr may be all the fun you'll want in that light rifle with that heavy slug.
Boy, 120 777 with a 350-400 grain bullet is a hell of a load in that lightweight gun. I agree.
I use 80 gns 777 in my firehawk. Have used 100 pyrodex regularly, but with that gun I shoot mostly sabot loads with 240 gns bullets.
FWIW, the Firehawk in stainless and wood is, IME & O, one of TC's finest ever.
