craig, it may not be the same, but what part of the explanation for Dell's conclusions don't apply to shotguns? The laws of physics, etc. don't change.
I and a few friends have been loading bpcr cartridges with light loads of Unique, 4227, and similar powders, then pushing 3/8" of fine-pore floral foam over the powder until it crushes. This also holds the powder on the primer and creates a sizable amount of space to the lead bullet. Accuracy is greatly improved in most cases. No problems have been reported.