I believe I could have a double problem though - Oversize primers and maybe excessive pressure.
Do you all think the Federal primers being as large as they are could have enlarged the primer pockets to begin with?
And should I back off from the 50.5grns as it did cause the primers to flatten some?
Could be---that 's what's FUN about this Fine and Pleasant Madness called handloading, isn't it?
It looks like you are narrowing the possibilities down really well.
My opinion; that .001 or less difference in diameter shouldn't cause all that much difference in fit, and should not expand a properly manufactured primer pocket.
A human hair is about .003", and an oversize primer plus an expanded primer pocket might provide an accidental better fit. Having said that, I have used Federales, CCIs, and WLR primers for years, always with Winchester brass, with no hint of a fit problem, even after multiple loadings.
New brass is a good idea, and the fact that your cases have been reloaded only twice and have developed loose primer pockets indicate that you may be running too high a pressure.
Primer flattening is one of the least reliable signs of high pressure, unless you pierce or crater the primer cup, or the primer shows no radius on the edge, or swages out to fill the primer pocket completely, but it IS something to be aware of.
What Groovyjack said! Most primers, even in factory loads will flatten to some degree, because the cups are made of a softer material. But, dropping the load is always a good thing, especially if you feel uneasy. .5 gr, or even a full grain of powder less will not make all that much difference, and a deer will not know if it is hit by a 100gr bullet at 2950 or 2900 fps.
Read the article on optimal long range loads somewhere else on the forum. It is a goodness. Thank you, Dallan!