The receiver was constructed from both stamped and machined components, spot-welded or welded together. The test model had a wooden lower receiver with two pistol grips – to be replaced by an integral plastic lower in the series-manufactured ones. The two grips combined with sliding wire stock were to facilitate accurate burst firing.
The design was made fully 9x19mm convertible by using a universal magazine and bolt face, by simple exchange of the barrel. In reality, only the 9×18 Makarov model was ever built and tested.
In 1975, test models of both designs were tested in Radom. The test minutes stressed the high efficiency of the R-75-IIs gas-dynamic retarder, enabling the rate of fire to be reduced to 635 rpm – deemed perfectly effective for such a weapon.
Radom R-75-II Specs
Caliber: 9x18mm Makarov
Muzzle velocity: 313 mps (1,029 fps)
Barrel length: 150 mm (5.9 inches)
Sighting radius: 269 mm (10.6 inches)
Length, stock retracted: 363 mm (14.3 inches)
Length, stock extended: 590 mm (23.2 inches)
Weight, empty: 1880 g (4.14 lbs)
Magazine: 15 or 25 rounds
Rate of fire: 635 rpm
Despite the encouraging results of the R-75-II trial, it was the other R-75, the R-75-I, that was selected for further development. Some of the rejected prototype’s ideas (namely the dove-tailed front sight, and four-position sight flip) were carried on to the winning proposition, which was deemed better suited for mass-production and adoption. The folding stock was replaced by the sliding butt of the R-75-II, fitted with a folding metal butt-plate in the PM-63 Rak tradition. The stock struts were now made of round bars, sliding through the stock hinge, dropping and getting latched upon extending. The extended and latched stock was oblique to the axis of the bore, enabling the shooter to use the sights placed low on the receiver. The stock latch positioned inside the receiver required extension of the receiver – which was used to provide it with a thicker rubber pad.
As a result of further development, in 1981 a test-series of 10 R-81s (pm wzór 1981) chambered for the 9×18 Makarov were ordered for testing. As a result, another batch of 20 was ordered with a different handguard, now sporting a folding fore grip in the PM-63 Rak tradition. At that point a suppressor was also designed for the new SMG and an external thread was added to the muzzle of the barrel extended because of that development from 150 mm to 165 mm.
The R-81 retained the Skorpion-style button cocking handles. These were later replaced by more extending ones due to problems with cocking the weapon in winter gloves. Button cockers were replaced by the ones shaped like the original plastic ones – but machined out of steel for durability.
Vibration during shooting trials caused the one-piece receiver connecting bolt to crawl out, despite the springing tab, cut from the bolt’s side. This was thus replaced by a two-piece one, with two concentric bolts, one within the other, inserted from either side and blocking each other – just like PPSh 41 receiver hinge pin, but of course much smaller in diameter. After the tests, the receiver was ordered to be made of thicker gauge of steel – but excessive flexibility of the receiver remained the number one problem of the Glauberyt ever after, right until the PM-98 radical modification.
After the specified amendments were made, the submachine gun was adopted by the Polish Army and security forces as pistolet maszynowy wz.1984 (PM-84), and ordered into mass-production about 1985 – but tooling and preparation for the initial series (serialed in “PP” – like Prototype Pistol – range) production took several years to complete. At that time a special modification for the internal security anti-terrorism unit was prepared, fitted with a suppressor and a 1st generation laser sight, not much smaller than the gun itself. The first complete guns were manufactured as late as 1990, which sealed their fate effectively. Despite positive test results and favorable reviews, the mass-production of the PM-84 never happened. A feeble attempt at conquering the civilian market was made with the semiautomatic-only version, called the Semi-Automat, but restrictive gun licensing policies killed that initiative and nobody abroad was interested in such a weapon chambered for the 9 mm Makarov.
The overthrowing of Communism gave an additional boost to the already discussed and prepared move of upgrading the personal-defense caliber to 9mm Luger. In 1992, a decision was made to introduce the 9mm Luger as a military caliber and seek a modern, polymer-framed handgun with companion submachine gun in the new caliber. The PM-84 project was shelved for good.
In its original concept, the R-75-I was to be the dual-caliber firearm. This was still a viable option at the time of the R-81, but only one 9×19 barrel for the 30 R-81s was made, as after Martial Law was declared in Poland by the hard-line Communists on December 13, 1981, all export contracts to the countries outside the Soviet zone of interest became a matter of fantasy. Besides, all the 9×19 ammunition at that time had to be imported, as its domestic production at Mesko was only complemented, and early experiments were conducted with it not earlier than 1983, with mass-production starting in 1991. So, when changes were made to the receiver, magazine and magazine well, nobody seemed to care if these modifications prevented shooting 9mm Luger. To make it dual-caliber again meant some degree of re-designing anyway, so a decision was made to abandon it altogether and re-design the PM-84 completely, this time basing it on the larger round.
ZM Łucznik’s management pre-empted the strike, starting the re-design as early as 1991, on its own initiative, and – not at all typically for the Radom factory – with their own money.
In 1992 when a decision was made to adopt 9x19mm and start developing a plastic-framed handgun (which led to adoption of the Wist-94 pistol), Radom was already able to bid a replacement for the PM-84 in the form of the PM-84P, a redesign of the older submachine gun.
Adding the P (for Parabellum, as the 9mm Luger round is called 9mm Parabellum in Poland) in the model name was a very modest token of what the change really meant. The redesign was complete, and thorough. Some changes were made to cater for the more powerful round, some to facilitate manufacturing. Most of the internal parts of the mechanism were left alone and are completely interchangeable between the two guns, but some parts had to be re-dimensioned, then other re-shaped to fit those re-dimensioned. The bolt had to be made larger and heavier, and so also the receiver and pistol grip, housing the larger magazine. Unfortunately, the magazine catch was among the few parts left alone, which was a dire mistake. The magazine catch was a temporary fix made overnight while building the R-81 prototypes, and left untouched later on, because it worked well with the 9×18 Makarov magazine. The design of that catch is truly horrible: it’s safety-pin style spring is impaled on the grip plates screw, which forces the shooter to set it anew with every thorough cleaning of the weapon. The screw in question is totally unsupported by any metallic surface – in the field, this part of the grip was frequently chipped-off, especially in winter, when the plastic parts were frozen. As a result, the magazine catch was lost – and so was the magazine, and the weapon became useless unless the magazine was held in the magazine well by hand.
As the 9mm Luger was a much more powerful round, the older suppressor was too small. A new one was not designed so the external thread was eliminated. Dimensional changes needed in the sights were also used to simplify them and change the layout. In the PM-84 the rear sight was fixed, only the flip-blades were moving, while all zeroing work was done by screwing the front post up and down in a dovetailed front sight base. The new front sight base was fixed, and the front sight post only moved (screwed) up and down. The rear sight riveted axis was replaced by a micrometric threaded bolt – the flips could be rotated about it, and the thread could be rotated to move the sight laterally between the sight protectors. As the 9×19 had a much flatter trajectory, only two settings were needed between 50 and 200 meters, instead of four. The cruciform sight leaf was retained through – it was patented by the factory and thus a source of royalties. The two redundant arms of the cruciform were used to put sight notches doubling the peep-holes set at 75 and 150 meters.
A sling eyelet was added to the front part of the receiver. This was a result of the creeping change in the tactical role of the PM-84P. The PM-84, as well as the earlier incarnations, the R-75-I and R-81, had only a bottom rear eyelet, behind the pistol grip, where a PM-63 style, single-point sling was fastened. No more points were needed for what was deemed a holster-carried firearm. The PM-84P, though, was not handy and small enough to enable the holster-carry, and so a two-point sling was issued for it, enabling it to be carried across the torso in combat, with holster being only a transport container.
In 1993 after the prototype tests, which indicated among others a higher rate of fire in spite of the heavier bolt (the ROF climbed from 600 to 640 rpm), the PM-84P was ordered and mass-production preparation begun.
Another police laser-sighted version appeared, this time with a much smaller laser, stored in the underbarrel-box, under which the folding fore grip, carried from the PM-84 into PM-84P, was fitted. Several, up to a dozen units of these laser-sighted Glauberyts were made for the Ministry of Internal Affairs.
Before manufacturing began, the old-style small cocking handles were replaced by much larger ones that protruded up. Only then the Army adopted the new SMG as the pistolet maszynowy wz.1984P (PM-84P) and true manufacturing started. Even today, the PM-84P are a vast majority of the around 60,000 Glauberyts manufactured to this date.
The experience of use by the late 1990s of the PM-84P by the military and police enabled the realization that the requirements of the two services are different enough to warrant replacing the “universal” PM-84P with a service-specific police model. In the military, the SMG is a PDW, Personal Defense Weapon as a secondary weapon for tank crews, artillery gunners, drivers, clerks and cooks. In police service though, it was a basic source of deadly force, a main armed combat asset in patrol or escort duties and in combat against organized crime. As such, it was not to be carried in the holster, but slinged at port arms, or across the chest, with stock extended. Its predecessor, the PM-63 Rak was also employed for tactical use by the Police – mostly for the lack of the better gun, as it dramatically lacked pinpoint accuracy. Most of the Police special unit Raks had their fore grips folded and duck-taped shut, because they were not durable enough. After the political changes, SMG tactics was based on Israeli practice, which never used the fore grip for the simple lack of it in a Uzi. The Police assault teams needed means to put tactical lights on their SMGs rather than folding foregrips.
The first attempt at making a better suited Police Glauberyt was the so-called Police PM-84P of 1996. The grip was replaced by barrel-shaped handguard, returning to the original 1975 idea. The useless flimsy buttplate (in most cases duck-taped open anyway) was replaced by the fixed, oval, at least three times larger one, fitted with a concave rubber overshoe protecting against slippage of the butt-plate from the shoulder. At the same time the profile of the front sight was changed from rectangular to a conical one.
This were steps in a good direction, but not far enough, and the Police did not order it. Soon, after the military order was completed and not renewed, in 1997, ZM Łucznik SA set about another thorough re-design, this time with Police requirements as a guideline. The result was the ultimate Glauberyt, the PM-98.
The stock was completely changed; even though save for the fixed buttplate it looks identical. The stock struts were replaced with twice the diameter, and more robust rods. The retracting knobs were re-modeled again. First, a left side knob was abolished, along with its corresponding slit in both the receiver and the receiver cover – only the ejecting opening remained on the left. The retracting knob was enlarged again, thinned, looking like a raised canine ear – and so (‘Ucho’ or The Ear) it was nicknamed by the operators. The fore end was similar to the 1996 proposal, but with a socket in the front of the handguard for the light or laser module. If neither tactical light nor laser sight is used, the socket is filled with a screw-in plug to protect it from debris (or if plug is lost – duck-taped over). The sling eyelets were re-organized again, this time to enable using a three-point sling. The PM-84P had both eyelets placed on the bottom, which caused the slinged weapon to turn upside down. To counter it, the PM-98 had all the sling eyelets welded on the upper part of the receiver.