I buy denim at the yard good store. mostly using 10 ounce for all the guns now. When Taylor first built my .69, it would not shoot 10 ounce (.682" ball) over 90gr. of powder
or it would blow holes in the patches. I had to use 12 ounce, I measured at .025" with the mic and .030" compressed in calipers. That worked all the way up to 1,700fps, which
took 200gr. GOEX 2F. Shot the same as 165gr., so I stayed with 165 for my moose load. Shot a bunch of 1" to 1 1/2" groups at 100 meters with that load combo. That was in the 80's.
Might be able to do 2 1/2" to 3" today. I made 2 1/2" a few years back, shooting with Taylor, but had 4 shots in less than 1 1/2".
I am a firm believer it takes powder to shoot well at long range. More powder, also gives you a longer point blank range, given reasonably low sight height.
I wash new denim twice. First time, regular wash, second time, same cycle, but without soap. Rinse twice. The material usually comes out slightly thicker than it measures in the store. Safe
to say that with a ball .005" under bore size, 10 ounce should work well. It might even work with a .010" undersized ball, as long as the rifling is normal, not the deeper rounded bottom grooves.
A .600" ball is already .010" undersized to every land. It's no wonder those thin patches were burned through. Even the light load shows blow-by all the way around.
Keep at it, you'll get it shooting well with a hunting load.
I found Swiss 1.5F to be heavier per stricken load(volume), than GOEX 2F and 3F.