Breechplug
The heavier bullet will only preform better up to a certain yardage befor the lighter bullet wich retains more energy will out preform it at the longer distances.
You might want to re-read your statement I think you might have it just backwards... Normally the lighter bullets will not carry the enrgy as far out as does a heavier bullet unless the velocities at the start are really far apart or the BC of the bullets are severly mis-matched. Again assuming that they are close in diameter.
This might serve as a comparison...
