I no longer use the Mk12 SPR or any 5.56 rifle cos this is often the case. However, within 100 metres a 5.56 will drop a target after 1 hit to the centre mass...not sure if the ballistics/damage model factors in potential body armour though.
Agreed, the damage model is quite weird. Takes 3 centre mass hits with the Mk12 SPR at 200-300 metres to drop a target. I'm pretty sure 5.56 is more potent than that.
@ Uranium - I'm assuming you are firing at the engine block/fuel tank area?