I would have to say that filling "big black powder cases" with black powder would be a safe bet.
Certainly, but as you point out, people do try all sorts of equivalents. I've wondered if any of those involving smokeless powders are safe.
I can see where a hang-fire might generate some gases which later go off, these gases forming something of a super-primer. This would light up the main charge far faster than a regular primer, and the result would be similar to having used too fast a powder, ie. the entire charge burns off before the bullet is far enough down the bore.
However, I'm not sure I see why a light bullet is required in the recipe. Does this mean the light bullet jumps down the bore a bit more, giving a larger (and cooler) combustion chamber, allowing more gases to cook off? If so, then a heavy bullet should have a similar effect if the charge is reduced further still.
always use ninety to a hundred percent of a case-filling charge
Is Hodgdon playing some odds in advocating greatly reduced charges of H4895? How about the BP folks shooting light charges of 4227 and 4198 in the medium length (eg. 38-55 and 45-70) cases? Or is it only the heavily deterred powders which create problems?
