Originally Posted by ACEd

Agree significant differences in metal geometry at top. It is also worth noting there were 2 variations (at least for the 4516-1) with the yellow follower, the original with the D shaped indent at the back and the AcuGlide without the D but with different, more severe lip geometry. I dont have mags in front of me, but based on pictures I took for previous post in the referenced thread, I believe there may be subtle changes in followers, potentially very minor changes in the ramp angles. Still the metal changes stand out.