Dirtier? Yeah, maybe, but "they" cleaned up Unique in recent years - it's not as dirty as the Unique of old. I too like Hodgdon's shotgun powders in pistol loads, having made that discovery after giving up shotgun sports and re-employing the leftover jugs of Clays and Univeral Clays. But that's coincidental, a matter of expediency and accuracy, not because it's cleaner. I still have, and shoot with, a stash of the old Unique and don't mind its "dirtiness" - after all one cleans one's guns after a day of shooting anyway, right? As for schmeck left in the barrel after each shot, it gets blown out along with the next shot and matters not a whit.
