Midway has been selling several Mark 4s as exclusives for years. So no its not a different animal. Our military used all of them and Midway has been one of the few vendors you can get them from. The fixed 10x is probably tougher than the variables which were not all that great for a couple guys i know who had them on hard kickers.

https://www.leupold.com/blog/post/30-years-of-service

I meen i dont see them listed as available thru Loopie. Maybe im missing it?
https://www.leupold.com/shop/riflescopes