Think about this. Over the years we have made some 13/16" (.812) diameter barrels in 50 cal. I am not going to tell you
about the ridiculous test loads we did in one. The biggest problem in using a barrel this small is cutting dovetails into it
If you don't have a vertical mill to do it, I would suggest you solder them onto it. Personally, I would never build a gun
with a barrel this small. We have also made some 3/4" barrels in small calibres, but have discontinued that, too much
like a "toy". Years ago we had a guy here in Pa. who was shooting in a lot of matches and winning more than his share.
He shot a gun with one of the 13/16" 50 cal. barrels, shot 50 grains of powder, and was deadly with it. As for me, I
would prefer a heavier barrel for target shooting...............Don