Gas

A gas blowback pistol or rifle stores propellant inside the magazine and uses it to drive both the BB and the slide cycle. Run out of gas mid-game and the pistol's a dead weight at your hip. Use the wrong gas for the platform and you'll either underperform (gas too cold) or risk damage (gas too hot). Three propellant types cover the UK GBB market, each with different operating characteristics.

Green gas is the UK standard — propane mixed with silicone oil, sold in red-capped cans (Nuprol, ASG, Abbey). Optimised pressure for most GBB pistols (~120-130 PSI at room temperature), built-in lubrication from the silicone oil, the propellant nearly every GBB pistol is designed around. CO2 is the high-power option — sold in 12g cartridges that slot into CO2-compatible magazines, runs significantly higher pressure (~800 PSI from a fresh cartridge), gives sharper recoil and higher FPS but stresses the pistol's internals harder. Not all GBBs accept CO2 mags — check before buying. Propane with adapter is the value option — bulk-buy a propane cylinder from any camping shop, decant into your gas can via an adapter, costs a fraction of green gas per fill but lacks the silicone oil lubrication (mitigated by oiling magazines manually).

Gas also powers 40mm grenade shells for launchers — usually green gas for compatibility with most shell designs. And cold weather is the killer of all gas propellants: below ~10°C, pressure drops sharply and cycling becomes unreliable. The fix is either heavier gas (winter-grade variants exist), CO2 (more cold-tolerant than green gas), or HPA pistol adaptors which bypass the gas problem entirely.