So my state requires a ML pistol to be single shot and at least .50cal to be legal for deer. So my Remingotn 1858 is out.

I have parts from an old New England 12ga, the stock/receiver and foreend. I have no idea what happened to the barrel assembly, I inherited these as parts from my grandfather.

I was thinking of getting a 1:28 twist Green Mountain barrel and manufacturing the correct mounts to turn this into a break-action ML pistol. I would either cut the stock down to a pistol grip, or use it as a pattern to carve a purpose-built handle to get the length of pull correct.

Question is, how long of a barrel, and .50 or .54? I would probably mount some sort of Red Dot sight on it and use it for shots out to about 100 yds.