What kind of gas are you using? Are you charging the mags correctly/fully? Also, about how warm is it where you're located? With the weather here in Edmonton the way it is, my room (where I store my mags) is still pretty cold, far below the ideal temperature range for GBBs. Cold mags will exaggerate cool down problems inherent to gas guns and result in poor performance and gas mileage. If you have long (49 round) mags, they tend to perform better in the cold simply from having much greater gas capacity.
Don't shoot your gun sideways. It releases fast cooling liquid directly into the gun, and would likely cause damage similar to venting the mag with the button on the back (frozen seals and the like). Also, the hopup will badly skew shots made from anything other than a correct vertical angle. Firing sideways also expends MUCH more gas with no gains in performance whatsoever (even though more gas is expelled, the rocket valve will close under similar pressures, so the BB will be propelled with roughly equivalent force and the rest of the gas wasted venting on blowback).
*edit: You know, I was just thinking about this today... The whole no increased fps bit made sense to me when I was considering the way the gun works, but there are plenty of contradicting examples
high flow valves and enhanced hammer springs all work by releasing more gas which apparently does make it past the floating valve to improve fps. Still, don't shoot your gun sideways! It's still more likely to cause damage and poor gas efficiently than firing it in the correct orientation.