I shoot the 348 grain powerbelts all the time out of my Staghorn with 90 grains of Pyrodex RS with great results. I also shoot 320 grain real conicals with 100 grains of Pyrodex RS, again no problem. I have shot conicals that are 426 grains with 80 grains of Pyrodex RS. No accuracy there, but no damage to the rifle. I have even shot minnie balls out of the Staghorn. Again with 80 grains of RS and no damage to the rifle. The thing I would do is keep the charge under 100 grains, and the larger the conical, the smaller the charge.

I have also shot conicals over the 300 range, although with the Staghorn I seem to find that it likes the lighter conicals. The 240 & 250 grain range.