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C02 pistol are very affordable and they are very high on FPS. There are two types you can get a Blow Back C02 Pistol or a Non Blow Back C02 Pistol. The Non Blow Back is cheaper and has more FPS and the Blow Back is more expensive and has lower FPS but with lower FPS you get cool blow back action where the slide moves back after every shot but nothing comes out just the bb out of the barrel.

Magazines- Most Non Blow Back C02 Pistol have the C02 put in the grip of the pistol where you slide the grip to the right and there is a slot to insert the C02 cartridge but you still put the magazine on the grip of the pistol. Now Blow Back C02 pistols have you insert the C02 cartridge in the magazine as well as bbs where the Non Blow Back has separate places for each.

They are really easy to use and they are really fun. In my opinion you should get a Non Blow Back C02 Pistol because you barley are starting in airsoft guns you should get this one at Walmart it's a really good deal.

http://www.walmart.com/ip/Crosman-Air-Mag-C11-Soft...

Most newer CO2 airsoft pistol just have the gas go into the mag. All you have to do is get some 12g CO2 cartridges (They sell them at WalMart, Academy, etc.) and place one into the slot in the magazine. Once you do there should be a cover that goes over the end to conceal the cartridge and also screw it into the mag so that the air valve punctures the cartridge's seal. Make sure it is in tight so that the air does not leak, but do not over force it and break the air valve.

How To Use Co2 Cartridges