Hi AmEngRifles. I have only shot new production Wolf bimetal in my semi Mk3. This ammo has a boat tail bullet that does not play well in older bolt actions, but cycles and shoots fine in my Bren. Just a thought. Has the regulator been drilled oversize? I would think that the smaller holes would be modified, as they are not useful on a semi. The only concerns I have heard for the cordite ammo was mostly about hang fires.