The Swift Magazine is likely based on .45 ACP magazines for the M1911.
Despite being classified as military ammunition, it is reloaded with one box of civilian bullets.
It is found in civilian, and sometimes military locations. It is used in both a weak and strong firearm, the Colt and Desert Falcon respectively.
As with all magazines, combining two of them together will get you the sum of both magazines filled into one, while still retaining the other. (Assuming there would be rounds left over in the second magazine.)
An empty magazine has the same texture as a full magazine on the ground.
It somehow has the capability to chamber rounds into the Colt and Desert Falcon, despite the two being incapable of sharing calibers in real life.