co2 is much higher pressured than green gas so it will give you a fps boost of about 20-40 and if it's blowback it will kick harder but if you have a low priced gun you risk cracking it! so i recommend that you get a green gas gun because the 20-40 higher fps does not compare to replacing your gun! But if you do decide to get a co2 gun DON"T get a m1911!!! My brother got one and it broke within 2 months!