Well I learned something today from the local gunsmith and thought I would share, probably already been covered but worth posting again if not. I recently sold my model Remington 700 .300 Ultra with a Nightforce 20moa Pictanny rail and figured I could just use my used Seekins rings
off of that rifle for my new Savage model 111 LRH .338 Lapua equipped with a factroy supplied 15-20moa? Weaver rail. Long story short I was wrong, the Seekins rings rattle back and forth on the Savage rail when torqued. Ended up ordering some Leupold Mark 4 rings designed for a Weaver rail and will see how that goes. Here is the information that I obtained from this little venture hope it helps somebody.
Picatanny vs. Weaver rail differences...
The only difference between the Picatinny rail and the similar Weaver rail is the size of the slots
The Picatinny locking slot width is 0.206"(5.2324mm). The spacing of slot centers is 0.394"(10.0076mm) and the slot depth is 0.118"(2.9972mm)
Weaver rails have a slot width of .180"
Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails.