Originally Posted by Strelok
Propane is pretty much the staple of any gas blowback to date. C02 if anything is a novelty/convenience to it. But it does have its benefits.
Usually C02 will shoot harder, and will be a bit more reliable than propane in colder conditions. If you live in an area where the temperature is generally lower. You should opt for C02.
Propane however is a LOT cheaper and reliable enough. 80% of pistols and rifles set for 'gas' run off of it. It just starts seeing some performance issues in colder or hotter temps. Really depends...
I just got a WE M4 CQBR and I was wondering why people prefered gas mags, then I started doing the math. 1 x CO2 cartridge last 60 bb's. $5 for 5 cartridges. 10 mags (as an example) mean $10 +tx. It's not very expensive but it's a lot more expensive then a propane cylinder (tank) at a cost of $3.89+Tx for a lot more mags.