It was the mp5 and the m9, and it makes sense why, as they both use .9mm rounds. I don't feel like this is a glitch as much as it should just be an implementation. Guns using the same type of ammo should share ammo, whether for the better or the worse.
Honestly I like the MK14 better for some reason...
I like how in CoD4 if you wanted to silence the 74u you had AR hip fire spread. This basically diversified what SMGs people would use (if you wanted to go stealth you'd be better off with the MP5 or P90).
Honestly CoD4 gun balance was the best... especially when you consider that CoD4 was original at the time.
GT: OhBlivEeUn "MW3 is a really stupid game. Not all jugernauts are alike? Strike packages? Get the F*** out of here." - BattleAxeRX