Hey,
I started a thread about this last year, it's here:
https://www.realitymod.com/forum/f10-pr ... ate-3.html
It annoys me that (playing as US) I can't reload my US rifle at a MEC crate but I can reload a found MEC rifle at a US crate. It's just inconsistent, and I while I understand that the engine limits how we can use crates, it doesn't prevent us from going back to universal supply from crates. This is a system that used to be in place and I honestly have yet to hear a single convincing argument for keeping the current system over it.
It may not be common practice for Blufor troops to use opfor guns and ammo, and why would it be, having trained with a certain weapon I'm fairly sure I'd want to keep using it in a life or death situation. However, if I was out of ammo in a hairy situation, I would pick up a G3 and use it.
So while i recognise that different factions use different ammo types, the current system falls foul of this anyway, and it would be be more "realistic" (in that it simulates using whatever you have to hand in order to stay alive, rather than just sitting there lemon like with an empty m16 next to a crate full of enemy guns and ammo).
Also, supplies are important in PR, they should be treated as such, and if found by the enemy there should be consequences.