As for your comment on gas types for gas blowbacks; co2 has more force to it, meaning the BB will have a higher velocity exiting the barrel. Green gas has less unf to it, so the BB will be traveling at a slower speed compared to co2.
Green gas is cheaper, since you can essentially use propane (Coleman 1lb tanks work perfectly) and you can find them everywhere. Co2 costs about $1 per canister, and the costs add up.
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