Do me a favor so we all can help you better: take a couple more pics for us. How about one of the bolt's face, and one of the base of the fired round that were hanging up. Also please measure the rim diameters and thicknesses of a round of the 120's that didn't cycle, and same for one of the brass that did properly cycle.
This is personally a new one for me as I have never seen this issue come across the boards here, nor have I had it myself.
Bookmarks