I just received an M1 and was surprised to see that the rings on the swivel bales are made of brass and not stainless steel as others. I compared it to the other M1's I have and all but this one has stainless steel bales. I looked up any info on this but all states swivel bales were made of stainless steel. It appears to be of Korean War era, rear seam. Was there a particular era that brass was used? P.S. it does not stick to a magnet as others do.