You say,'coke can shim (feeler guage?) gap at the top', thats about .002" (isnt it Tim?), and from past posts hasnt that been an acceptable 'headspace' on these? Now, is that a pinch 'fit' or a sliding fit of the feeler?
Have you removed the extractor/ejector for the fitting? No need to be second guessing the breech fit with it in there to throw you off.
With it out, can you get that feeler down around the sides too?