I notice that the bottom of the grip on the 3953 Tactical has an extension to match the bottom of the magazine in length when inserted. Is this part of the grip or the frame. What would be the purpose of this?I would think it would be easier just to have the bottom plate of the magazine extended so when inserted the bottom of all 3953's would not have that notch that exists when magazines are inserted.

I believe what you are referring to...

there are two models of TSW

standard grip length with a standard 3913 type mag
and
shorter grip length utilizing a CS9 type mag

the latter is for better portability, but by all means dont go slamming a mag home without moving your finger out of the way.

I qualified with three big service guns and slammed mags home. when I went to qual with the CS9D and I did my first mag change....well let's just say it was not pretty.