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The Degtyaryov machine gun was a Russian 7.62x54mmR light machinegun from the late 1920s, the initial prototypes used a pretty par for the course 20rd box magazine, but with the DP27/DP28 iteration, it would instead use a horizontal drum (or 'pan' magazine).
The Degtyaryov uses a long-stroke gas piston to motivate the bolt carrier, which locks with a pair of 'flapper' locking lugs which get forced outwards by the firing-pin slamming forth on its way to strike the primer, forcing them to engage (thus, the action would HAVE to be locked to be able to fire). The recoil spring on the DP-28 machinegun is coiled around the piston rod, which was regarded as a sleek way to keep the action short. When the gun cycles, it actually makes the drum/pan index each cartridge, so when it fires you see the magazine spin.
It's a very old fashioned looking machinegun, with its old style rifle stock, the horizontal drum, and conical flash hider. It worked really quite well, the magazines being a single stack made them reasonably flat, so with a carrying box to stuff a bunch of them in, reloads weren't TOO cumbersome, and with its relatively high 47rd capacity, it's more than twice most magazine fed light machineguns of the era.
Compare to the Chauchat (20rds, but really 18rds), the Browning Automatic Rifle, Lahti Saloranta, and Zb.26 (20rds), the MG13 and Châtellerault, (25rds), Bren (30rds), or Madsen (20rds to 40rds, depending on variant and caliber). It has the same high capacity as the Lewis gun, but without the bottom of it being open to the elements, and the single stack nature keeps it fairly low friction and well behaved.