Why would they want to?
If you are training & doing I.A Drill's. (Imeadiate Action) & load/ unloading Drills as well as live firing in service. You WOULD need dry training to be as near to live firing as possible.
So.......Troops would use 'Normal' 30 rounders. If you want less drill rounds in a 30 round mag. You only put in what you need. Simple!

WHY on earth would the Military go to the trouble & unessacary expense. Of getting a different type of mag in?....

Of course, if YOU needed a 10 round mag. It would be a simple job to cut one down, & modify it.

Just my 2cents worth of being a Military Armourer.