I found a bag of 100 of these sorting through my piles of gun stuff. Any idea who made them for midway?

Is that the Mannlicher Schoenauer cartridge or the rarer Mauser? I would guess it is the former.

Just curious.

Just the regular M S variety.

Midway has used Jamison and Star in the past. I used their 25 Remington Brass (Jamison). It was heavier than factory brass but worked great in my Rem M8 and the quality control was very good.

Call Midway and ask.

I don't know who made Midway brass but I, and I have heard from others who experienced the same, have had several potentially dangerous longitudinal splits upon firing after the first reloading.
The guy who sold me the rifle didn't reload so I am certain the brass was only once fired. The splits occurred just below the neck and ran down about 3/4" or they occurred starting about 3/8" above the base and ran up the case about 1/2".
I tossed the rest of the Midway brass and loaded rounds, about 17 pieces, after my experience with the splits.