This photo was taken of a Cobra helicopter. You can see the gun pod houses twin mini guns. The gun pod housing has an interesting warning painted on the side.

WARNING-GUN WILL FIRE IF ROTATED BY HAND

This is not something one typically realizes unless you have worked on or around mini guns.

To prevent negligent discharges there is a way to stop the barrels from spinning.

See that rectangular hole in the OD green metal bar? A rod is inserted up into that hole to physically block the barrels from rotating.