This is a spare magazine for the G&G G1911 fixed slide NBB CO2 pistol.
Note: CO2 pistols live relatively short lifespans. CO2 is a very high pressure gas, is unfiltered, and is also dry. Particles from CO2 capsules can deform the hard rubber and plastic seals used in CO2 valves. You may have to replace the magazine periodically to keep this pistol in working condition and every time you put a new CO2 capsule in the magazine, make sure to put a drop of 100% silicon lube on the puncture valve.