I screwed up the title and don't know how to change it. I have a Ruger MARK III 22/45 Tactical and just today I purchased a Ruger MARK IV 22/45 LITE, SKU 43927. The magazines for both look identical except for the finish. My Mark III magazines are a dull black finish while the Mark IV magazines are E-Nickel finish. I see no difference except in the color of the finish on the magazines, yet Ruger says it is not recommended to use Mark IV magazines in a Mark III gun and vice versa. Can anyone tell me why? The magazines look identical. Is Ruger just blowing smoke to get people to buy more magazines? Has anyone tried a Mark III magazine in a Mark IV gun? If so what was the outcome? I'm specifically talking about the Mark III 22/45 and the Mark IV 22/45 LITE. Thanks everyone.