During a few playtests, we've come to like playing a rule best summed up as an Operations Card:

Low Ammo: Your units firepower is halved AGAIN for any attack (Fire & Movement, Concentrated Fire, Op Fire, Assault) action.

IE A russian squad containing 4 regular infantry makes a Fire & Movement. They move two hexes and fire on a german unit. They would normally attack with a FP of 2, but with Low Ammo, it is halved again for a FP of 1.

or

A russian squad of 1 officer, 1 elite, and 2 regular infantry assaults a german squad. They normally would assault with a FP of 5, but with Low Ammo, assault with a FP of 3 (2.5 rounded up).

This has made for some gruesome urban onslaughts where one side may outnumber the enemy, but still depend on combined fire and other tactics...