I've had patches that were just "too thick", not too big for a .30 cal. At least on a round jag.
Because no-one seems to standardize on thickness I just keep a .270 jag tip handy for the really stubborn ones, or use a slotted tip.
Allan Quartermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”