If you can find arrangements to get a tank filled with high pressure air, pcp guns are great. I have a 22 cal that I tuned to a little less than 900 fps with the heaviest weight 22 pellets, and I can shoot maybe 25 shots with very little change in point of impact, then another 25 or more but it slowly drops point of impact as pressure falls below a certain threshold. Sorry, I've forgotten the specs of pressure vs number of accurate shots as its been a while since i shot it. I brought home my scuba tank from the last hydro test, and the buggers forgot to fill it.
I can also quickly turn down the velocity to some degree. When it shot at 495 fps, I could get a lot of shots out of a tank.