I passed up 4-5 Mark II magazines at the gun show last weekend. I purchased 2 Mark III magazines on Ebay and one turned out to be a Mark II (they turned up after the show). My stock 22/45 Mark III functions fine with Mark II as well as Mark III magazines. I was wondering what is the purpose of the extra notch on the Mark III magazine (The magazine catch is lower on the body of the magazine.) Thanks Neil S.