[firespec35]

Where exactly were you? It depends on what state land you were on. IIRC state recreation areas, Target shooting is prohibited even if hunting is allowed. It has to be specific areas to shoot (State game areas etc...) I can't remember exactly because the only public area I shoot at is the pit in lapeer.
As for confiscating your guns. Welcome to the DNR. They have more unbridled power than any police agency. Good luck. Call a lawyer
ETA* missed the part where you said its local pd. That's crap there yours you were legally carrying them. Take your ri60s in and get your stuff back. As for the rifle hopefully you have the reciept. If it wasn't reported stolen they shouldn't have taken it.

PS My gut is saying there is more to this story. Maybe it the gut of a cynical old ghetto medic, but my gut is right more than wrong.