Nope they should both be 7/8" The only difference is some have different recoil lug layouts and widths as picatinny is a military thing and weaver is a civilian thing. Kind of like the big debate about 5.56 vs .223 rem. Virtually the same thing but not quite.
There are of course exceptions to every rule, but for a good rule-of-thumb, “Picatinny” accessories won’t fit Weaver, but Weaver accessories will fit “Picatinny”.