Requirements: FNV (of course) and Gun Runners' Arsenal add-on. It's sold by Vendortron as "Buffalo Gun."
45-70, I figured it would do a little extra damage and have more critical chance and damage than a regular Brush Gun, but made it heavier and with a regular 6-shot magazine to keep it reasonably balanced.
I liked the versatility of the Medicine Stick but prefer scopes for long range. I used the La Longue Carabine model and animations, but the sounds and settings from the Brush Gun and Medicine Stick to make a scoped levergun with decent power.