Cast a few hundred last weekend. Was loading up some 45 colt and noticed a ring around nose of all my bullets. Thought it might be my top punch and switched to a flat one. Come to find out it’s my seating stem on Rcbs cowboy dies. Alloy was ww air cooled. Doesn’t do it on my bullets from the Lee mold but meplat larger on the NOE mold. Strange it didn’t do it when loading in the summer. Thinking of grinding ring off the stem and being stuck with a flat tipped seating stem but hate to tear up my stem if anyone has a suggestion. Not sure with same alloy why it didn’t do it on the 1000 or so I loaded in the summer and just started.