If those were OM inert projectile 76 mm shells , they like to 105 mm and earlier 3"/50 had bagged powder charges inside the cases . The muzzle debris were bag parts . The bagged charges in 105s are in lighter and coarser cotton than flour sack , just a long skinny pillow case with a draw string top and an over powder card to give near zero case space after projectile seating . The typical powder kernel is by eyeball about .20-23×.675 with 7-9 longitudinal perferations basically 4831 scaled up 10x or so . The powder is bagged on a tare scale separately from production lines to eliminate powder spills . If you've fumbled a full case lately or had a measure bridge unload after you moved the case or pan you can imagine 10-20# going on the floor except it screws up a whole semi manual hydraulic 5 cell assy line when there's a spill .
The light for twist and after exit waiting for the spin and air drag to catch up is pretty obvious too . I don't know right off what a 76mm standard weight projectile is but TNT weighs about the same as concrete and era APs generally had a weighted core behind a hardened point and a faux nose cap for BC bump , one hold over book for 6 projectiles of slightly different weight and MV to hit the same POI at 500 & 1000 yd . You only have to be 150 ft with a fragmenting shell at any range but you have to be inside 30" to disable another tank with an AP or EP . Probably 12" for a kill unless you have the high ground and can shoot the engine room . Again in the era .