DP-28 vs DPM

I’ve mentioned the DP28 and DPM light machine guns a couple times, and it occurs to me that the differences between them are worth going over. There are parts kits for both variants available, so a prospective builder ought to know what changed and why.

DP28 (front) and DPM (behind)The DP28 was one of the early generation of light machine guns, designed between the World Wars before everyone had figured out which features worked and which didn’t. During WWII, the Russians adopted a modernized version of the gun as the DPM in an effort to improve some of the more readily fixable issues.

The most obvious difference between the two guns is the stock. The original DP28 used a traditional straight rifle stock with a bulge for the non-shooting hand to hold. The DPM changed that to a much more comfortable and controllable pistol grip. In the process, the grip safety was dropped and replaced with a safe/fire selector lever above the trigger. For someone contemplating a semiauto reproduction, these are the most significant differences between the designs.

DP (top) and DPM (bottom) stocks and lowersFor guns in combat use, though, the change to the recoil spring was much more important. The original DP28 used a recoil spring sleeved around the gas piston, under the barrel and in front of the action. It was discovered that under continuous fire the heat from the barrel was intense enough to damage the temper of the spring and cause malfunctions (the same thing happened to the Lewis gun for the same reason). So with the modernization, the spring was moved to a more typical position behind the bolt. There was no space in the receiver to accommodate a spring back there, so a tube was added to house it. Incidentally, this change also forced the change of the the takedown pin – the DP28 uses one the runs through both sides of the receiver but this would interfere with the recoil spring in the DPM, so it uses a shorter pin that only threads into the near side of the receiver.

DPM spring tubeIn addition to the spring housing tube, a guide for the rear recoil spring was also necessary, to prevent it from kinking and binding. So while the bolt and locking flaps were left unchanged between the two designs, the DPM added a long tail to the firing pin to act as a spring guide.For what it’s worth, I have no idea what the three holes in the DPM bolt carrier are for, but they show up on every DPM kit I’ve seen.

It’s worth noting that the receivers for the two designs are basically identical, and a DPM receiver can be assembled with a DPM pistol-grip lower and DP28 internals, including the forward mounted recoil spring and still function just fine (unless you’re shooting so much that you get the barrel glowing). This is a convenient fact for semiauto builders, as the lack of a recoil spring in the back opens up a lot of options for a semiauto fire control group.

DPM (top) and DP28 (bottom) bolts and carriersThe final change was to the bipods. The DP28 bipod was just clamped over the barrel shroud with a thumb screw, and was deemed too weak in combat. So with the overhaul, the DPM bipod was changed to a unit that used a bracket inside the shroud solidly bolted to an outside piece to hold the legs on much more securely. In additions to being more solid, the result was also attached at the top of the shroud, giving the DPM a slightly lower profile.

DP28 (top) and DPM (bottom) bipods and receiversThere were other variants of the DP light machine gun, including vehicle-mounted, aerial, and belt-fed types, but those will have to wait for another day. The two we’ve looked at here are the ones commonly available today as parts kits, and thus account for the vast majority of what most folks will encounter.

Pictures courtesy of GunPics.net