I have been reloading target shotshells for over 50 years without a mishap, so far anyway
Given the bulk of such powders as Green Dot, Unique, and so on, if I have a double charge of 32 grains in a 12 ga hull I can't get hardly any shot in, so I see a problem right there.
Unlike pistol brass, too easy to put a double load in a 38 Special hull, that's why I charge the hulls and put them facing up in a block 50 at a time and shine a flashlight down to see they are all level with the powder before seating the bullets.
A big worry is to have no powder in the primer will blow the bullet halfway up the barrel = a bulge