approx 600-850psi, normally around 750-850psi (think the pressure of CO2 at room temp). since most, well, all stock class nelson based pumps run off twelve grams, and none of them comes stock with a reg, that range applies to pretty much all of them. the on exception might be the garg, just because it comes with a spiffy valve chamber that can be enlarged a bit, but even then the gun still operates at the pressure of room temp co2 in the stock config. I mean, I've turned many a stock class gun to lower/mid pressure operation with a reg and some other things (i.e. springs) but they certainly don't come stock like that.
How's you project going? XD