It's not the OD that's the problem; it's the shape of the primer and it's slightly greater length that makes them hard to seat. The Remingtons are slightly shorter have a more rounded nose. The plastic in the base of the STS hull conforms to that shape. The longer Winchester primer has a square nose and the plastic in the end of the STS primer tunnel interferes with it.
: You can seat the primers as deep as possible and fire the shell. There should no be as much of a problem after the first reload. OR you can use a #1, an A, a 15/64 or a 5.9mm drill bit to manually ream the STS primer hole to remove some of that plastic. I've tried all of them and prefer the 5.9mm or 15/64. I put the drill bit in a drill press set on slow speed hold the hulls upside down while I ream the primer hole from the outside bottm. Takes only a second or see for each.
Typically, the Mec and Lee loaders that push the hull down onto the primer with support from the inside will insert non_Remington primers much better than do the P-W loaders that don't give the primer tunnel any internal support. I use a P-W loader and keep a little Lee Load-All close by. I pre-prime a thousand or so Remington hulls at a time with Winchester primers on the Lee then unscrew the primer punch pin from the deprimer of the P-W and run the hulls through pre-primed the first time I reload them
Maybe these photos from another forum will clarify: <I>Remington Hulls and Non-Remington Primers</I>