dont you need green gas to fill those?
and how much does 1 fill of green gas last in a gun
I agree, if you want a high quality airsoft marker then you should get a gas marker. Also, don't use CO2, get HPA. It costs a buck fifty to fill up my HPA tank here in Southern Colorado. I've seen the same prices in Germany, Oklahoma, Massachusetts and Indiana, so I'm pretty sure it's the norm.
The reason I say HPA is because it is a more stable gas. CO2 has to be stored as a liquid inside the tank, therefore it's cooler (which I'll explain the effects of that later), and it has to be converted to a gas before it can be used to fire the projectile. Unfortunately, if you fire too fast the chances of siphoning liquid CO2 into you marker increases which will freeze up your marker and can cause a bunch of damage. Also, because the liquid to gas conversion, there is an inconsistency in fps. The paintball field that I regularly visit here, doesn't allow CO2 tanks on the field anymore because if you're firing at a chronograph you'll get mixed reading. It's usually +or- 20. So a marker calibrated at 280fps can shoot 300fps to 260fps. If you're playing speedball which is usually in-your-face action, then you won't see much of a difference, but out on the scenario field you might as well try to look as formidable as possible, because you won't hit much.
Furthermore, the boiling point of CO2 is -70 degree Fahrenheit. So that liquid CO2 is ccooollldd. The problem is that if you're playing during the fall or early spring months, you will find your marker siphoning up that liquid CO2 more often than during the warm summer months.
HPA is stored as a gas, and is warm. Eliminating all of the above problems.
Anyway, I'm not an airsoft expert, but I have played paintball for 11 years. So that's my reference for this post, personal experience.
My advice, since you all ready have a spring, you can at least go play. Just save up your money for a high quality gas marker.