But having to deal with each shell hardly makes HPA worth it. Also it seems the easiest place to tap would be the rear plate on the stock, which wouldn't be compatible with shoulders
I don't even think tapping it would work because it's got the little chamber for the CO2 cartridge and then the valve inside it that lets a tiny bit of unregulated CO2 (around 800 PSI) through to propel the bb.
It's kind of like the same concept with a CO2 pistol. I thought about tapping one a long time ago and then realized that it probably wouldn't work. Also, the chamber walls are probably very weak since they aren't actually holding the gas, just the metal cartridge.
I agree though, if it was possible to tap, it probably wouldn't be worth it. I wish manufacturers would spend more time on making rifles that are accurate, consistent, and durable rather than things like this.