I'm not sure a 15/16ths inch TC barrel should be bored to 62 caliber. If my Chinese arithmetic is correct a 15/16ths inch barrel is;
.9375 in diameter. Subtract .620 that makes total meat left at .3175. Divide that by 2 for two barrel walls and what is left is .15875 for barrel wall thickness.
Normally a .62 fowler barrel diameter back at the firing chamber is larger than an inch, and probably closer to 1-1/8th inch leaving much thicker barrel walls back where ignition is. Plus, the fowler barrel tapers slowly to the thin section. A .62 caliber 15/16ths inch TC barrel will be thin, slightly over 5/32 inch all the way back to the patent breech.
Every one of these I have heard of were done using a 1-inch TC barrel.
Bob