If I had to guess, since Jim uses the same barrel, just bored to different calibers, it will be a .50, .54, .58 selection. If he has a tapered barrel, and personally that would be make or break for me to buy, I would think that squeezing in a .62 would be tough...maybe not since the pressure is so much less 'out there' at the end. After all, on a 20 GA fowling piece the metal isn't too thick at the muzzle. A .50 would be heavy as I suspect a tapered barrel will be 1 1/8" at the breech.
I'm watching this one with great anticipation!
I'm watching this one with great anticipation!