suitable ammo for CO2

Whether you choose a pistol type or a rifle type is up to your taste. Personally I prefer rifles, simply for the pride I derive by handling them. Maybe your like for the pistol type is just ungovernable – go for it! The better the air rifle feels in your arms the more you are likely to enjoy your fun plinking or target shooting or small game hunting. Just note that the pistols have lower muzzle velocities than the rifles because of their shorter barrels.
This goes hand in hand with the look. Oh yes! My preference has always been the hardwood stock. I’m no person to walk around with synthetics, no matter how closely they are tailored to resemble wood. If you are a synthetics guy, still well and good. There are lots of CO2 rifles with synthetic stocks.
Finally, consider the accessories that come bundled with the air rifle you choose. Some CO2 airguns come with good quality scopes while others have no scope at all. Some have picatinny rails for mounting of extra accessories while others are plain.
What kind of ammo (pellet or BB) should you use for a CO2 air gun?
Pellets and BBs come in several different types and shapes. The ones you choose will depend on what you are using them for.
Air gun users can broadly be divided into target shooters, fun plinkers, and hunters.
If you are a target shooter, the wadcutter pellets will do you good. These are able to cut an accurate hole on the card stock of the target. Referees can therefore analyse the scores without much uncertainty.
If you intend to plink soda cans all Saturday afternoon, I suggest you use the round nosed pellet – round because you do not need any penetrative power. You can also opt for the BBs in this case. For your information, BBs are round or spherical while pellets have a more aerodynamic shape. It pays to know this.