If I remember correctly, the bodies themselves were originally made for the Bingham rifles. I remember reading that Ciener purchased thousands of these Bingham mag bodies initially. The magwell block (lack of better description) was added to the Bingham mag bodies by Ciener for use with the AR-15 conversion kit. Then later, he started making his own mag bodies. The pic below shows the weapon that used the mag.
I remember reading that same thing so I started looking for hi-cap mags that I could modify to use in some of my rimfire uppers.
This is something I did and what I found so far!
the mag on the Left is built with a box around it and I use it in my M261 17 Mach2 upper. I found the actual magazine body in E-gunparts.
The middle one is a modified Ciener 30 round mag I use in my M261 22lr upper.
The mag on the right I found in E-gunparts and the body looks just like the Ciener but is listed as a 15 round Mossberg magazine and has a little box thing on the top rear. When I got it I found the mag body seemed to be exactly like a Ciener but the inside parts mere a poor copy. All the Ciener internal parts fit in this mag. One reason it may have been listed as a 15 round mag is there were two springs inside -- I removed one spring and can load 20 Mach2 rounds and 25 22lr rounds in it. These aren't cheap at $27 from E-gunparts plus the shipping but I wanted to see how close they were to the Ciener mags. I'm starting to think these are made some place in Europe and then modified by a second manufacturer to fit different guns.