Fold Crimp versus Roll Crimp

[Cap'n Morgan]

With a shotgun shell, the wad is always seated against the powder, unlike some rifle and pistol loads where the bullet seating depth varies the distance from the bullet base to the powder. Deeper seating reduces this distance and that's where the higher pressure comes from no?

Yes, but all shotgun wads are somewhat compressible - some more than other. If you have two loads with exact similar components, a roll crimp will in most cases (pun intended) compress the wad less, resulting in lower pressure.

[Squid Boy]

The wads were not always seated on the powder. Some early Paradox shells had a collar inside that stopped the wad and left a chamber where the powder was loose. It sounds crazy but it moderated the pressure in early smokeless powder loads and will still work today. Thanks, Squid Boy

[Newtire]

Just curious where did this info come from?

[Squid Boy]

I am sorry to say that I cannot put my finger on it at the moment but it was either The Gun and It's Development by Greener or The Modern Shotgun by Burrard. It may also have come out of a compendium of articles from The Field. There are several others as well but this was linked primarily to the Paradox Gun and H&H. I have been working with Paradox loads quite a bit lately and will post the info if I can locate it again. Thanks, Squid Boy