There may be nothing more confusing in the world of gun accessories than trying to define the scope mounting system. Picatinny, cross slot, Weaver style, scope rail, and 1913 mil-std are all terms used, but ask anyone to explain the difference and you might just be met with a blank stare. There are those who would claim that they are essentially the exact same thing, but is that in fact the case?
The answer to that question is a resounding NO!! The Weaver and Picatinny scope mounting systems were not standardized at the same time, with many even believing that the Weaver style was very much influenced by the Picatinny design.
That may explain why there are some definite similarities when you view each base head on. As far as mounting purposes go, their dimensions are interchangeable, but when you look at both from the side, that is when the major differences become painfully obvious.
What is that difference, I hear you ask. The most obvious difference is that the cross slots on the base of the Picatinny system are wider. These are the slots that the recoil lug or bolt on the rings fit into. It should also be noted that the slots on the Picatinny system are evenly spaced, whereas the Weaver system will place slots where they believe is most suitable for mounting a scope.
If you are wondering whether or not your Picatinny rings will fit in a Waver style base, the answer really depends on the size of the recoil lug in the rings. Weaver style rings almost always fit just fine in a Picatinny base.
More information about the dimensions of both styles can pretty readily be found online. The one word of advice that we do offer is that if you are set on using Picatinny Scope rings, you will probably be much better off with a Picatinny base.