The DShK is a gas operated, belt fed, air cooled machine gun that fires from an open bolt and in automatic mode only.The gas piston and chamber are located below the barrel; the gas piston is of the long stroke type, and is attached to the bolt carrier. The gas chamber is fitted with a gas regulator, which requires a special wrench to make adjustments.
The bolt, of generally rectangular cross-section, locks into the receiver with two outwardly pivoting flaps. These flaps are pushed outwards from the bolt to lock it by the enlarged firing pin, which in turn is operated by the vertical projection on the bolt carrier. The rear of the receiver houses two spring buffers, one for the bolt and one for the bolt carrier.
The heavy barrel is finned for better cooling, and is fitted with a large muzzle brake. The barrel can be detached from the weapon, but it hardly can be called “quick detachable”; it is screwed into the front of the receiver, and then fixed there by the cross-bolt,which is also screwed in place.
There’s an entry on the DShK in Wikipedia, too, but it’s pretty spare.