just for giggles 
Mossie 25% fuel and full ammo - 17,913 lbs
Mossie 25% fuel and all 303s gone - 17,711lbs
Mossie 25% fuel and enough 20mm for a kill - 17,291lbs
so not as much of a dif as the jug but still it's an advantage of just over 600lbs
as grizz says, it's not much in most planes but it is in some.
Thx for proving me wrong, it is definitely an advantage in the jugs. I think the best way to look at it is the ratios of weight being fired off, not necessarily the poundage. In the case of the mossy, dumping ammo with 'enough to kill' gives only a 4.5% decrease in weight. As for the jug, dumping ammo gives 7.5% decrease in weight. As far as trying to establish some sort of a guideline for which gives 'noticeable advantage', I'd say >5% decrease in weight = noticeable advantage, <5% negligible advantage.
As far as these types of rules in a tournament like this with nothing on the line? Meh, no need for it. If you get a jug as your dueling aircraft, dump ammo!
P.S. I'm willing to bet the 110G might also gain a nice advantage also but since it is already a heavy 2 engined aircraft, the percentage difference in weights might be similar to that of the mossy, <5%.
