Well OK,go down the page just a bit and look a Grump's posting of the BD Load.
Grumps a freind of mine and we both fired that rifle he speaks of a few weeks ago. I guarentee that shallow groove fast twist false muzzle easy loading plastic thing WILL NOT shoot a full lead bullet with any accuracy.
There ain't enough rifling to grab the lead.(period) We shot that thing for hours.Tried 8 different projectiles.
We did find an ok verticle group at 50 using 365 gr full sabot type projetiles in front of about 70grs 2f t7,and determined if a feller cleaned the bore with a proper plastic cleaner stuff it would get better.
I found the Black Diamond to be just a little too light for me,it could use a little more weight in the butt end to give it better balance,and a funny thing happened with the trigger about 3 times out of 50. It was almost like a hang fire but it was with the mechinism,pull the trigger and it did nothing,2 seconds later it went off,scary,we just figgered it needed a break down and cleaning.
Those in-lines can be just as fussy for proper load and lube and prjectile as any of the traditional BP guns'. It just takes experimentation to find it.
To answer the original question, no there is no generic powerbelt type projectile,anything better than those cost more money.
Ya might tell ole'Dave just for me; that a patched round ball can out shoot'm all :-D , it has for centuries,the other are just a passing fad. :lol: