777 has never burned thru my .018 yellow prelubed pillow ticking patches. Many looked reuseable after picking them up off the ground and that was using the hotter-still FFF 777.

Like most others have stated here, I'm in the same group that believe you are probably looking at a .530 ball and either .015 linen or .018 pillow ticking.

What powder?..... I use real blackpowder these days...... Schuetzen or Goex FFF. I got tired of seized nipples and seized cleanout screws from 777.