I have three of them. Two flintlocks and one percussion. They have a 1-28 twist. They are basically the same barrel you'd find on a Knight Rifle. Very excellent sabot shooting rifles.
Mine like the 240 grain XTP with about 85 grains of powder. I have pushed them harder, but I found the very best accuracy was with 85 grains. I have pushed them all the way up to 110 grains.
They are well made, easy to clean, and just a great barrel. Depending on the year of your Hawken, you might have to customize the barrel a little to make it fit. I had to take a small amount off the thimble rib that rides under the barrel, so the stock could accept the barrel. A Dremel tool made this just an easy thing to do.