Sharps I ahd Jason Simpkins in Colorado make me a double rifle in 50-90 caliber from a Merkel 12 gauge. It is a fine conversion gun. While I am not an expert by any means I believe he goes up to 50 cal in 12 gauge donor shotguns and is working on a .577 on a 10 gauge shotgun donor. He has also built 45-70's on what I think were 20 gauge frames.

Barrel length is whatever you want, basically. I wanted a short stopper gun and Jason did a fantastic job of making mine a 20 inch barreled fast wielding stopper gun that is as about as powerful as a 500 Light NITRO, which is enough for stopping about any beast on the planet. Blam Blam.

His brother is on this forum. Bonanza. I encourage you guys to work out best ways to reach Jason if you want to talk to an expert in conversions, like Jason is.

I have a 50-90 double rifle on a beautiful Merkel frame that shoots great, looks great, and cost me a fraction of what a 50 cal double rifle that is this beautiful would cost.