BFG- that looks like an exceptional light offhand rifle, doesn't it.
My .45 has a GM barrel with 60" twist. It likes both water based lubes and oil based lubes. With the water based, it shoots well with from 55gr. 3F or 2F to 75gr. 3f or 2F - all GOEX. With a slippery lube, like Shenendoah or LHV, it demands 75gr. 3F or 85gr. 2F. That is to shoot 1/2" bench groups at 50 yards. I use a 10 ounce (.0225") denim patch with .445" ball. It shoots equally well with the red/white/blue/blue ticking (.023") I send to a couple people. Measurements with calipers squeezed hard (between finger and thumb), not a mic, which measures thinner.