Hi Rabid...
well my original post didn't take.. so here is the short version.
That rifle is White clone and those bullets are meant for the 1-24 twist. Your Hawken type gun won't probably shoot them real well, and my New Englander split the stock with the 440 version of the same bullet.
70 grains is all you need with the white to get these accurately downrange. At 1100 feet per second, the bullet has 550 revolutions per second, enough to stabilize. This same velocity would give you only 275 rps in the hawken/new englander with 1-48 twist. You might have to really push this with much more powder for it to be really accurate in your gun.
Aloha.. Tom