At one time, Ram-Line made at least one hi-cap mag for the MKII (14 rounds). It had a semi-transparent plastic body, with a "constant tension" spring or some such thing. The spring kind of "rolled down" as you loaded it. Closest analogy I can think of is like an exposed tape measure with the end secured inside the top of the mag. I think the spring design was the reason they were able to cram so many rounds in there.
Someone also made a 12-round mag with a stainless or chrome-plated body. I think this one was by Ram-Line, as well. IMHO, this one looked a little better, at least on paper. I've never seen one in person.
Back in the day, they were both listed in the Cabela's catalog with the 10/22 stuff, etc.
I've got a 14-rounder laying around somewhere, but I've never shot it. It didn't exactly exude quality, but when I saw it I couldn't help myself! Someday I'll dig it out and try it...
I think there would be a market for a higher-capacity mag,
IF it would function as well as the factory mags. A 14-rounder that functioned well and worked with the Ultimate Clip Loader would pretty much be ideal. Not exactly a Bullseye tool, but it would make the tin cans dance! Spray and pray...
