The nose of the propeller-head slug looks a shade larger than the Gualandi's and I think it is unlikely that it would set off a primer under normal shotgun recoil. But Elvas is right, and ''think it unlikely'' is something it might be an idea to improve on. A concave ejector pin would very likely be enough.
I don't know that ballistic coefficient is such a great issue with shotgun slugs. Everybody is some way off having their range limited by loss of velocity rather than loss of accuracy. A possibility worth considering, though, would be a plastic sabot covering the nose, into which the lead part is inserted from the rear. The nose in plastic could be any shape you like, and besides primer detonation, would deal with the tendency of a slug cartridge to fall on and dent the slug nose when dropped. I don't think lead could ever decelerate faster than plastic. It would probably need a plastic plug to fill the space behind the slug.