Glen Seekins, from Seekins precision is who clued me in on the details of Picatinny rail. His bases and rings (some of the best I've ever had) are true picatinny spec, others are not. The problem arises when you try to put a ring of Picatinny standard on a base that's not, The slot in the base won't accept the lug under the ring. The reverse of that Picatinny base with weaver ring, is a sloppy bolt running through a slot, this could allow the scope to slide for or aft. Either case is not good. I have three Slug guns for deer hunting and a muzzle loader for deer hunting here. They all have picatinny bases, this way I can swap the Leupold 2-7x scopes between the guns if needed, I also can easily remove the scope and replace it when cleaning the muzzle loader. even the newest greatest muzzle loader are still a chore to get as clean as I like them.
Paul