So after sleeping on it, I think this is a a combination of things.
1. The wall thickness on the Win brass is slightly less than spec (~0.010-0.011 as best I can measure with calipers).
2. The pulled plated bullets are slightly swaged down (just over 0.400) and should be 0.401
3. Possible that my brass is work hardened and not sizing properly anymore
I have a hard time believing that my brass is over worked. I have a quite a bit and most of it was once fired range brass (some mine, some purchased) that is fairly new but I couldn't tell you how many reloads. I try to load it first in first out, I have a return bin and a supply bin so I keep all of it in circulation and don't just reload the same pieces over and over. Plus you would think I would see split case mouths if the brass was work hardened I haven't seen any during loading 40. I have had a couple with my 45 brass.
I took some measurements of the case mouth diameter through the loading cycle.
Sized: 0.419
Expanded: 0.421
Seated Bullet: 0.422
Crimped: 0.421-0.422 (tried different amounts and none leaving crimp mark in bullet)
I've set my expansion to the minimum amount that would easily accept the bullet so it doesn't teeter on the case mouth. it's much less than I was using prior as you have to get the bullet just right for it to sit on the case mouth.
I think I'm going to try the EGW small base die for these pulled plated bullets. I don't think I need the Lee U die as it is 0.003 smaller, it would just work the brass that much more.
So now the million dollar question, what should I do with the ~500 loaded cartridges that could potentially setback? It does take moderate force to get the bullet to move. Should I run them through the crimp die again? I don't think it will do any good.
I've shot maybe 1000 of these without issue. I'm leaning toward just shooting them. Knowing they may setback, I won't just hammer the slide if I encounter a jam. What do y'all think?
Thanks to everyone for their input.
Cheers,
Toby