The Hawken rifle was being made around 1820... even in percussion lock versions.
They would have been cutting edge technology.
Few mountain men used percussion rifles. They knew
if the caps were lost, the gun became a club..
Much more likely he carried a flintlock ....could have
been a Hawken (St. Louis style)....Just as likely was a
musket or mid caliber (36-45) rifle.
These guys made do with what they had. In 1820, the
fur trapper was truly an explorer. Chances are they wouldn't
even be aware of what it took to take down game or even survive in the
region until after they arrived......No internet, phones, few newspapers.
It was all word of mouth and these guys were often misfits and loners
who didn't hang around asking a lot of questions. After all, who were they
going to ask? The fictional movie version
of Jeremiah Johnson being a notable exception).