Have you noticed that movies and paintings always show mountain men carrying their rifles across the saddle. This method would make the rifle readily available in case of hostilities. It would also work as long as you were riding out in the open plains or scrub land. Much of their trapping activity actually occurred in mountain country that was forested and covered with blowdown, making this method completely unworkable. Don't think they had very many groomed trails back then either. On a recent black bear hunt in the Absaroka mountains, we constantly had to bust our way around blowdown or through aspen groves with no trail to reach the high country. My rifle stayed in the scabbard while I used my free arm to fend off branches and stay in the saddle. We also climbed up some slopes that required the horses to lung their way up to more level ground, making the task even more challenging. Heading back down out of the mountains in near dark one night, the outfitter's horse suddenly jumped about three feet sideways when it encountered grizzly scat on the trail. I got to witness a micro rodeo with colorful language in a tangle of aspen trees. No loose rifle would have survived that dustup. I guess reality doesn't always match creative presentations of history.