This condition is called "detonation". There is a camp of reloaders that believe that small volume powders in 38 and 357 are dangerous and they avoid that recipe altogether. The theory is that the low volume of fast burning powder spreads out and lays flat on the side of the case (because the gun is obviously level to the ground when firing). When this happens a rare condition can occur where the primer ignition travels over the powder (which is laying on the flat part of the case) and does not ignite the charge.....the primer pressure can start the projectile down the barrel before ignition of the powder charge and when the powder does ignite....kaboom.
My opinion is this "detonation" theory came from reloaders that blew up their gun and can't admit they f***ed up and made a double charge.....and are blaming it in the powder recipe.
I've had many spirited debates about this.......I don't subscribe to it. Bullseye is a fast burning low volume powder.....literal mountains of bullseye have been loaded under 38 wadcutters and semi wadcutters by bullseye shooters for decades.....2.7 to 3 grains at a time. It was and is one of most popular bullseye recipes.