Ok, after some additional thought and some measurements here is something that may help.
Thinking that you may be having a headspace tolerance issue, I did some measurements on the primers. These are approximate:
WIN 209: 0.2994"
Rem KB:0.2935"
So, the Remington Kleenbore's are 0.0059" shorter than the WIN 209's.
Perhaps this is just enough difference to be causing you the blowback because the Rem's are not sealing up as well in your rifle.
A couple of additional things I would check:
1) Check the main pivot pin in your rifle that secures the barrel to the frame,to ensure that it is tight and not loose at all. This could cause blowback. If is loose, then you will need a replacement main pin.
2) Don't over tighten your breech plug. Just snug it up finger tight. This may reduce enough headspace clearance to seal the Rem KB primers against the frame side of the breech.
Good luck!!
Tahquamenon