This actually makes me laugh out loud! Do yourself a favor, check the weight of the aircraft before you fire all the 8mm Mauser ammo from the rear gun and then do it after you have expended all the ammo. How much weight did you save? Do you think it *really* helps the you and the 110 to survive? If you need to be that extra 100 pounds less in weight to survive, then you should not have been in the predicament u were in. 
I make mention of that to everyone I see doing that, it is just a "gaming the game" thing that as you mentioned gives you an advantage in your own mind, when in fact it makes such a minute different that even if modeled you wont be able to notice. Think you'll be able to hang on that stall turn *that* much more because that ammo is gone? Nah, you wont. Dont waste your time firing all your ammo. It is just as much of a fable as "resetting the map room" will allied troops if a few enemy troops made it in. Time alone resets the MR. Skuzzy said it in the server.
This is wrong. The AH physics do not just ignore reduced weight because it happens to be borderline negligible. It does make a difference. The next question is - how much difference? That little bit of difference is marginal, but then it's not rare that you lose a fight because of some marginal angle or timing. While it's not something you should worry about when you're still learning the basics of an aircraft, IE when that marginal weight difference is "in the noise", once you get near being able to consistently enough fly an aircraft at 9/10th's or so, it's a worthwhile handicap -- Because: What's the alternative?
Having that much more weight being lugged around? If hit% stats matter less than having a good fight or surviving longer, then there's no reason not to ditch that ballast; if that's all that ammo is to you.
And this is not just theoretical argument, it's from practical exp. I can definitely feel the difference between 50% and 100% ammo in the planes I knew well, e.g. 152. I could feel it in the 110 as well, whose ballast-able ammo I'm pretty sure is at least as significant as the 152's. I regularly emptied my 152's down to something like 200 20mm and 45 30mm for most sorties. Sometimes dumped all the 20 and kept only 30mm. Why? For a reason that might be more particular to cannon birds, but: because I didn't need more than a handful of cannon rounds for a kill. And I got to the point where I only fired when there was an actual 30% chance I'd hit (and handful of 20+30mm = kill), and in most sorties there was only enough fighting happening to add up to about a dozen kills tops.
Now the above very specifically discerns what the conditions are that warrant dumping useless weight, even marginal weight. It's not for everyone, but it's definitely not "a fable".
