It is my understand that Old Gabe shot a hawken that was either .53, or .54 caliber, depending on sources, and not .58 caliber. I understand his rifle is still on display in a mueum out west, along with his possible bag, horn, and hand made powder measure. Someone else' memory is going to have to tell us which museum its in. Someone said its at his rebuilt fort, in Wyoming, but someone else said its at the Museum of the Fur Trade, in Nebraska.
Considering how the curved buttplate is intended to be fired off the upper arm( above your bicep), I don't think you want to volunteer to shoot many 150 grain charges out of such a gun, much less be packing two .58 caliber round ball in the barrel and firing. Those are " Proof loads ". and were never intended to be used off the shoulder.
A piece on his gun and powder measure appeared in Muzzle Blasts back in the late 1980s, or early 1990s, and indicated that his powder measure threw 50 grains of FFg powder. This for a .54 caliber gun. In an interview with the man in his later years, after he went blind from cateracts, Bridger said he used one measure when shooting deer, and antelope. He used two measures to shoot Elk and Black Bear, and three measures to shoot Grizzley and Buffalo. He also explained that his reasoning was so he could recover the lead balls , and recast them, as hauling enough lead around was a serious problem for men who trapped and hunted for a full year between supply sources, mainly at rendezvous.
I have my doubts about the writer of this story. I think Gabe used whatever was in the barrel to shoot whatever he came across. Yes, he may actually have planned to hunt a particular animal, and then could choose how much powder he would load in the gun. But, most of the time, I suspect he loaded his gun for what he thought he might find in the area. I doubt that he purposely hunted Grizzly bear, since they are such tough animals to kill, and were well respected for their courage, and willingness to attack a hunter if he did not kill the bear with his first shot, even when mortally wounded. Bridger's time around buffalo would also have been limited. There were no trains to take hides to market, so when he shot Buffalo, it was for food. The mountain men preferred to shoot the calfs, because the meat was sweeter, more tender, and the tongues were excellent fare.
If you have never eaten beaver, its the closest meat to taste like Beef you are likely to find. I can see how the mountain men got tired of eating beaver, and even venison, and looked for something different. They all write well of eating mountain lion, and considered it a great treat.
