A 45 Colt in a 410 chamber is not safe, as has been mentioned. Also, the OP said:
My local state park only allows squirrel hunting with a shot gun
I don't think the game warden would be amused to find you shooting a bullet into the air, even if technically it was fired from a shotgun.
There is a big difference between a 410 slug and a 7.62x39 bullet. A 123 grain 30 caliber bullet is somewhat light for its caliber. A 109 grain 410 slug is ridiculously light for its caliber. It has a very low sectional density, a function of weight for diameter, and won't penetrate very well. Couple that with the poor accuracy of a projectile fired from a smoothbore with no sights and you have a recipe for wounding.