Smokeless powder shouldn't explode. Black powder OTOH supposedly does. I've heard the same about pistol cartridges exploding with normal charges of Bullseye. The explanation being that the charge of powder lies flat in the case and the primer flash passes over the powder and ignites all of the powder at the same time. Very difficult to duplicate I understand.
Actually, this is the opposite of true.
Black powder CANNOT detonate like HE as it is a low explosive whereas Smokeless powder can and will actually detonate under proper stimulus. It's CLASSED as a low explosive, or deflagrant, but can be initiated to high order. One can make ANFO-type charges using smokeless powder as well as detonating it using a primary such as acetone peroxide or PETN. Even blasting caps will often produce HE detonation in smokeless. Or det cord.
"Burning or lighting all the powder at once" ain't in it......detonation is a pressure related phenomenon. Kinda' like 'dieseling' a gasoline engine...... but not.
But kinda'
Meanwhile..... even using containment (large pile/keg, pipe or gerb) the dull 'boom' of black powder comes from making it's shockwave front exceed the Mach limit, maybe 2000fps is achievable but not actual "HE" class velocities.
Properly stimulated, smokeless will propagate at 15,000+ fps .....
tmi, I know but I feel these to be important distinctions.
IMO "reduced loads" don't get dangerous until they're brought down to less than 50% of listed loads. And then only with "overbore" chamberings. IME what you'll run into when dropping down only a few grains below minimum, especially with slow rifle powders, is much less dramatic, involving collapsed cases, sooty necks and cases, weird smells and textures (I've seen cases with yellow sticky goop in them, like the powder turns to caterpillar guts) but can result in some fairly dangerous gas jets.
WEAR THOSE SAFETY GLASSES YOU'SE RELOADING GENII!!!!!
Or just stay within established boundaries.
period.