"Duel Code 14 gas" likely refers to 
Duel Code Green Gas, a high-performance propellant for gas-powered airsoft guns, with the "14" possibly referencing its pressure rating (like a 14kg/cm² equivalent) or a specific variant, providing consistent power and silicone lubrication for internals, popular for warm weather use and capable of cycling guns that lighter gases can't handle. 
 
Key Characteristics of Duel Code Gas:
Type: Primarily Green Gas (but also Red Gas variants exist).
Performance: High-performance, delivering reliable power and consistent pressure for blowback airsoft guns.
Lubrication: Contains silicone to lubricate seals and internals, reducing wear.
Weather Performance: Strong enough for warmer conditions and capable of operating in cooler weather where lighter gases fail.
Variants: Available in different sizes (e.g., 150ml, 560ml, 600ml) and power levels (like "Power Up 14KG").
Use: Ideal for gas blowback (GBB) airsoft pistols and rifles. 
In essence, it's a premium green gas for airsoft enthusiasts seeking better performance and reliability in their gas guns, with the "14" indicating its strength level..