Nice! I set up a range earlier this year and had that same problem. The new 300 round mag for the DPMS works really well. I also converted it to HPA so there's no drop off. A 13ci bottle is good for ~1200 shots. New problem: the trigger is so heavy(~10#) that I now pull it with my middle finger because my index finger gets worn out.
I'm looking forward to opening up the bottle regulator and seeing how different pressures affect the performance over the winter. I've got a 10 yard shot in my living room. I made a cover for my television to make sure I don't accidentally put a round through it
I also converted a KWA for the same reason. I made a little holster/bottle holder that has a speed loader in the pocket for convenience. I go through 18 rounds so fast on this thing. Reloading was immediately a huge issue but with a few modifications to the magazine(drilled a loading hole/altered the slider so it holds in place) and the old school cheapo speed loader its a lot faster now.
I got it intentionally because the reviews said it was very inefficient--which means it's wasting a lot of gas on a strong recoil. That's not an issue with HPA and makes it a blast to shoot. The trigger is very good--tested at 3#.
