I have read, on one of the old gunboards, that the compressed black powder pellet for the .303 had a hollow core molded in for more complete ignition.
I found this, which seems to corobberate that:
"The powder charge was pressed into a pellet with both ends slightly rounded and pierced with a central flash propagating hole.
I can't find a picture anywhere though. Possibly because you'd have to destroy a collectable round to even attempt getting the pellet back out. It would seem to support the other information I found where the pill was wet moulded into some kind of die, or mold & then ejected & dried. I guess they did this instead of the "rolling into a sheet, smashing up & screening for grain size technique"?
Funnily enough I used to visit an abandoned plack powder mill in South Wales frequently, but I never found anything other than workers cottage gardens gone wild for a couple of hundred years & riuned masonry.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”