There are lots of shot-out Colt and S&W 1917 barrels out there. Don't know if you re-thread one to fit a Judge or not.
Ya, I have a 1917 barrel that lead a hard life. I now have the 3" barrel in hand. Have not measured the threads, but I could probably make the 1917 barrel fit the Judge frame. But, then I could just use a piece of 4140 round stock if I wanted.
I am going to chase down some 410 shot shells and pattern the 6 1/2" barrel first. Then either ream out or use emery on a split rod and a drill to erase the rifling in 3" barrel. Take a small square file and make 4 shallow but easily visible grooves back in. Top bottom and sides, angling the file a tiny bit. Then install it and pattern it again.
I know it isn't going to have much range. But with 3" loads using 6 shot I wouldn't be surprised if ir killed small game at 20 yds. I will test it to see what it will penetrate before I shot anything with it. Bird feathers are tougher than rabbit skin, but will see how much paper it will penetrate at what range and how dense the pattern is. Might only be a reliable 15 yard gun.
But, from an article in NRA shooting illustrated "Remington's 2 1⁄2-inch, 1⁄2-ounce, No. 8 shot .410-bore game load produced a muzzle velocity of 1,180 fps. Penetration ranged from 3 to 5 inches. At near-contact distance the gelatin showed massive cavitation.
But no mention of distance. If a 3" 6 shot load starts at just 1000-1100 fps it should still be deadly on birds at 20 yds
A daisy BB gun fires a 5 gr BB at less than 500fps and will kill birds and rabbits with a decent shot. The velocity of 1.6 gr 6 shot out of a 3" Judge is going to be over 500fps at 20 yds
We shall see just what it will do.