I think that all primers today are "Nominally" the same size. Once upon a time Rem primers (Old 97 size) were of a smaller dia than (209) Win, Fed, etal & primers for the .410 were also of a smaller size I believe. The problem today is that the Cheddites & possibly some other imported primers are just enough oversize that after using the pockets will be enlarged so that domestic primers are no longer a snug fit. This can be a plus for several times loaded cases in which the pockets are beginning to loosen, but once used the domestic varieties will no longer be a fit.
