UKM-2000: The Polish Successor to the PKM

UKM-2000: The Polish Successor to the PKM

The business-end of the Polish UKM-2000P in firing position with just the belt left out for safety reasons before the command is given. Note the profuse chrome plating on the feed lips, part of the machine gun’s feed-tray extending out of receiver. Without a belt of cartridges, the UKM-2000P is almost undistinguishable from the PKM. (MSgt Mariusz Bieniek, 16th AABn Combat Camera Team, Polish Army, November 9, 2010)

These called for a deep modernization of the PKM, going far beyond mere rechambering for the new round.  A whole new family of machine guns were called for, the UKM-2000P Infantry model with traditional fixed hollowed wooden stock, a folding stock UKM-2000D Airborne model (both based on PKM), and a solenoid-fired UKM-2000P Tank model, based upon the PKT, all incorporating modification to the the direct feed with M13 disintegrating links.  The new machine guns were ordered logistically compatible with PKT/PKM, meaning that all mounts, covers, belt-boxes, packaging etc. designed for the old machine guns could be retained to reduce the cost of re-arming.

The UKM-2000C was initially to replace the PKT in all T-72 and PT-91 main battle tanks, as well as BMP-1 infantry fighting vehicles and BRDM-2 armored reconnaissance vehicles.  That was never to be realized, however.  So far it was only integrated into the new Hitfist-30P turret of the Rosomak wheeled IFV, due to limited availability of the new machine guns, imposed by the new HCP management abrupt decision to drop military production altogether.

The UKM-2000C was initially manufactured in standard, right side-fed version, following the old Soviet arrangement of the vehicular mount.  It was hoped that the so-configured UKM-2000C could be a major export success, enabling other ex-Warsaw Pact countries to introduce a NATO-chambered machine gun for their military hardware, sparing them the cost of rebuilding cramped interiors to install Western machine guns.  These plans failed to realize, and this was one of the deciding factors behind HCP’s quitting machine gun manufacturing after spending considerable amount of work and money co-designing the new model.  There is also another variant of the gun, the UKM-2000CL, fed from left side.

UKM-2000D with a prototype detachable folding and telescoping stock.

First model UKM-2000s were able to feed from two different belts, the M13 disintegrating links, as well as the German DM1 non-disintegrating one.  However, after the testing, a decision was made to eliminate the DM1 capability and use the M13 links only.

As early as at the prototype stage a Mil-Std 1913 support was designed for the UKM-2000, but the military insisted on retaining the old-style tangent sight, which took up most of the feed cover.  Later on the new manufacturer, Tarnow Mechanical Works (also making the WKM-B) designed a new detachable Mil-Std 1913 support, going over the top of the tangent sight (because the military wanted to retain not only the tangent sight, but also the ability to use while the rail is mounted), resulting in an excessively high and wobbly mounting of the red dot sights.  As the UKM-2000 was to replace PKM/PKT, same accuracy and grouping was required, as well as service life and reliability.

Similarities and Dissimilarities
The most profound design changes in the UKM-2000 as compared with PKM/PKT are connected with the new methods of chambering and feeding.  This required a completely new feed mechanism, repositioned from receiver into the feed cover, new feed tray, and deeply modified receiver, bolt, bolt-carrier and barrel.  With feed direction and ejection opening required to stay put as per the TTR to retain PKT vehicular mounts, the chamber had to be moved forward, to be positioned in front of the feed tray, instead underneath, as in “legacy” PKs.  As a consequence the barrel had to be shortened from 605 to 547 mm in P/D models and from 722 to 636 mm in C models, while the receiver was extended.  The longer receiver required the bolt to be repositioned, as the bolt carrier retained its length.

The new feed mechanism is based on the MG 42 and SIG 710-3, which were analyzed during the design preparation phase – but is not a straightforward copy of any of the existing models, by the simple fact of the UKM-2000 being a right-feed gun.  The feed lever with transfer lever are actuated by the roller on top of the bolt carrier, and the belt is advanced one half round per each stroke by the two pairs of feed pawls.  The barrel latch was also retained unchanged but moved forward.  The original latch was buried under the feed cover and feed tray, now it has its own separate cover, hinged on the feed cover axis and opening to the rear.  The trigger mechanism and all external fittings are identical to the PK series, thus minimizing the re-armament costs.

Machinegunners of the 3rd Assault Company, 16th Air Assault Battalion during December 16, 2010 training at Nowa Deba Training Ground, Poland. The fast give-away between UKM-2000P and PKM is that the new belt has a distinctive black stripe on top of the cartridges because the rounds are loaded with the closed side of the links up. The Russian style PKM non-disintegrating belt was always loaded “sunny side up” with the cut-out part up, showing cases (although it would work upside down as well). Early UKMs had many problems with that, when under-trained “old-school” gunners, fooled by the resemblance between the two guns tried to make them work with M13 links loaded rounds up. (Cpt. Bartosz Januszewski, 16th AABn Polish Army, Dec 16, 2010)

Models and Prototypes
Three models were built, one each for every variant, and these were subjected to various military tests in early 2000, which they passed with flying colors.  Only minor changes were thus introduced into the prototype series of two each machine guns.  Hand-made parts of the models were now replaced with machine-made ones, which vastly improved the appearance of the gun.  The bolt-carrier, which was a two-part affair in the model was now replaced with a monobloc variant, the gas regulator of the UKM-2000P/D was modified, and barrels were shortened still, to conform to the PK transfer crate.  The return spring was beefed up to increase return speed – the more energy, the less chances that cartridge would stick in the M13 link or its Polish counterpart, the GSM-01, which tends to be a little stiffer than the original.  The feed tray guide ribs, as well as cartridge plunger and feed lever’s roller guide were chrome-plated to reduce friction.  Also, the UKM-2000D’s stock hinge was modified by changing the stock folding direction.  The working model had a right side-folding stock while the prototypes were fitted with a top-folding one to enable firing with the stock folded.  Prototype machine guns as well as first batches of the Polish 7.62×51 ammunition were ready for state testing in mid-2001 and the tests took place in late 2001 and early 2002.

Per Aspera Ad Astra (Through the Thorns to the Stars)
The machine gun testing was mostly done by the Military Ordnance Technology Institution of Zielonka, and was divided into four phases: general testing, field conditions testing, extreme conditions testing and endurance testing.  UKM-2000D s/n P-006 was used for extreme conditions testing involving 7,000 rounds, which comprised a dry (non-lubricated) gun function test, extreme elevation and depression functioning (80-85 degrees up and down), combined conditions test, high temperature testing (+ 50-70 Centigrade), transient temperatures (-5 Centigrade), dust and rain test, cold temperatures (-50 Centigrade), increased dusting combined with vibration (simulated transport conditions) test, functioning with different amounts of roll (upright, left side, upside down, right side), dust testing of the oiled gun, all shot within 5 subsequent days with no cleaning and lubricating allowed.  Afterwards, endurance testing was performed with the same prototype, adding 18,000 shots more, for a grand total of 25,000.  48 stoppages were recorded in these 25,000 shots (including 9 attributed to the ammunition), giving a malfunction ratio of .16%, well below allowed .2%.

Another test involved flooding the gas tube with water – the gun was immersed in water tank, tilted down to allow water out of the bore and then fired.  No stoppages or parts breakage occurred.

The UKM-2000P can pull as much as 2.5 meter-length of M13 links with 7.62x51 rounds.

The last part of the testing was the drop test, during which the machine gun, loaded and put on safety, was repeatedly dropped from 1 m on concrete slab upright and upside down, and then on a steel plate from 1.5 m, barrel or buttstock first.  No accidental discharges or parts breakage occurred.

After 25,000 shots the condition of the machine gun was checked.  The overall condition was found to be good and the initial velocity drop was much less than projected – to the point of firing all 25,000 shots from one barrel only.  But the most amazing result occurred in the barrel dispersion test – the barrel showed less dispersion after the test, than before it.  No headspace changes were found.

The last test laid out for s/n P-006 was the barrel obstruction test involving firing a round with the bore partly filled with sand.  According to the test regulations, the firearm would successfully pass even if totally written-off in this test, provided no dangerous fragments are emitted that were likely to harm the crew.  The UKM-2000 passed with flying colors: the barrel was bulged, the left bolt locking lug cracked and the receiver was slightly deformed, but no shrapnel were scattered.

All of these tortures were applied according to the standing Polish Army testing procedure manual, written in the 1970s and based on similar Soviet procedures, still employed today by the Russian Army.  These are much stricter and harsher than any Western testing procedures and only really reliable and durable guns are able to survive it.

The UKM-2000 in Tarnow
Even before the testing was completed in May 2002, the HCP decided to drop the military production and the machine gun, although successful, became an orphan.  It took some time before the ZM Tarnow, the only remaining machine gun manufacturer in Poland (specializing in 23mm ZU-23 automatic cannon) was persuaded to take up NSV and UKM-2000 production.  The Ministry signed a contract with Tarnow on November 28, 2003, for an initial 30 machine guns of the trial series (10 of each model).  These were ready in mid-2004, when another series of tests, somewhat less thorough, was held.  Afterwards, the UKM-2000 was introduced into the inventory of the Polish Army and renamed “Rod” (for rhodium, as per Polish “periodic table” code for small arms).  No military manual was ever issued for it, and the factory manual still refers to it as UKM-2000.

Prototype new stock for the UKM-2000D folded.

The left side-fed UKM-2000CL model was developed especially for the Rosomak wheeled IFV/APC program in the latter part of 2003 by WAT alone.  The Rosomak (a license-built Finnish Patria AMV) was to be fitted with an Italian OTO Melara Hitfist-30 turret, so a special left-feed model was designed to be integrated with it.  As the modification was limited to feed only in a tank machine gun, a new, mirror-image feed cover and feed-tray were used, with the rest of the gun remaining unchanged.  It all proved futile anyway, as the Italians had at the same time reversed the MG mount in their Hitfist-30P (for Poland) turret, to enable it to work with a right-feed machine gun.  For several years the UKM-2000C for Rosomaks was the only variant manufactured at all, as the military suddenly lost any sense of urgency in re-chambering the machine guns of the line units – the requirements of STANAGs proved much less strictly enforced, as they used to be in the old Warsaw Pact, and so the Polish Army had at the same time small-arms in both Eastern (7.62x54R for PKM and 7.62×39 in backwater garrisons) and Western (5.56×45 and 9×19) chamberings, not to mention the NSV heavy machine gun used in both .50 calibers, 12.7×108 Soviet and .50 BMG.

It was not until 2007 that the first UKM-2000Ps were ordered for the army; and even that in far from overwhelming quantities – 130 in 2007, 252 in 2008 and just 40 in 2009.  The most universal of the series, the UKM-2000D with its folding butt, enabling it to fit into vehicular top mounts without having to saw-off the butt, was not ordered at all, which would probably kill the very interesting detachable folding-and-telescoping butt designed for it at Tarnow.  The airmobile troops complained about the weight as the UKM-2000D is indeed about a pound heavier than the PKM.

So far, less than 600 UKM-2000s were manufactured in all its models and types.  Only first rate “export” troops, including crack airborne brigades, mostly operating in overseas peacekeeping missions, have had the opportunity to use these and mostly rate them high as a successful modernization of a very good machine gun.

The Land Forces Command stipulated that the sight-mounting rail has to enable using both a rail-mounted sight and mechanical sight in the full range of the latter sighting distances - i.e. up to 1,500 m. The resulting rail is of impressive size but dubious utility.