>>63957828
Only one of the rifles has a trigger.
The others have auto-sears rigged to fire as soon as the bolt closes on an live round.
Rifle 1 has a loaded chamber and a trigger
Rifle 2 and 3 have no triggers and empty chambers.
>pull trigger on rifle 1
>rifle 1 fires and the gas cycles the action of rifle 2
>rifle 2 immediately fires, the gas cycles the action of rifle 3
>rifle 3 immediately fires, the gas cycles the action of rifle 1
>see step:1
In "semi-auto" it fires in 3-round bursts.