by Jean-Francois Legendre
To meet the needs of specific feed-systems and weapon mounts used for aircraft armament, special cartridge belts must be designed and used. This article is intended to highlight the cartridge belts used with the MG 17 and MG 81 in caliber 7.92x57mm as used in German Luftwaffe aircraft.
The “Gurt 17”
In the middle of the 1930’s, the young German Air Force adopted two aircraft machine guns in caliber 7.92x57mm. Those two weapons were derived from the same prototype designed by Rheinmetall-Borsig. The light version, adopted as the MG 15, was used on a flexible mount and was fed by a 75-round saddle drum magazine. The heavy version, adopted as the MG 17, was used on fixed wing or fuselage mounts, and was belt fed.
As the mounts for the MG 17 were fixed, the first models of belts were designed only to be able to be rolled upon themselves and both lateral and helical flexibility were minimal. The very first model was composed of individual links; each manufactured in two parts, connected to one another by steel pins. Each single link is made up of a main body encircling the cartridge case and fitted with a tongue, the re-curved end of which engages the extraction groove of the cartridge. A second piece is fitted inside the main body of the link, also fitting the cartridge body, and which has both ends curled into loops for the insertion of the connecting pins. The two parts of the individual link are manufactured separately and then assembled and connected with pins. Therefore, this belt is of the non-disintegrating type. These early links were adopted under the designation “Gurt 17”.
Although accurate data is missing concerning this early belt design, the length was probably 250 and 500 rounds according to the known types of aircraft installations. Since the MG 17 could be fed from either the right or left-hand side depending on the mount configuration, two different models of belt starters were used to enable the introduction of the belt into the weapon. These starter-sections are composed of a long flat tag at the extreme end, then five short tags finally connected to the first cartridge link of the belt. All the flat tags are connected together with the same pins as those used between the cartridge links.
The “Gurt 17 n.A.”
Soon, it appeared that this link design, based on two parts fastened together by the connecting pins, was lacking sufficient rigidity against both lateral and helical torsion. Accordingly, a new belt was developed, still based on the principle of pin interconnection and therefore non-disintegrating. In this case, the two parts of the individual link are so manufactured that no movement is possible between them. The apertures in the body through which the second piece passes are reduced to a minimum, just three small slots, to stiffen the body. The curled loops for the insertion of the connecting pins are formed after the two pieces are assembled. A patent no. 64839 covering the arrangement of the individual link was applied for by the company Ruberg & Renner in Berlin on Feb. 27, 1936 and made public on July 8, 1937.
This second model of belt, besides the different design and manufacture of the two constitutive parts, also has the particularity that the positioning of the link in the cartridge extraction groove is no longer achieved by a recurved end but by a stamped dimple. Compared to the previous model, the steel sheets used seem to be the same, whereas the diameter of the connecting pins is slightly greater. This modified belt was adopted under the designation “Gurt 17 neue Art” (new model) and denoted “Gurt 17 n.A.”. In the meanwhile, the early model was renamed “Gurt 17 a.A.” (i.e. alte Art: old model).
The belts “Gurt 17 n.A.” are composed of non-disintegrating links the number of which varies according to the gun installation but is typically 250 and 500 rounds. The end of the belt is equipped with a starter section organized for either right or left-hand feeding. Some early production belts may be found fitted with the starter arrangement of the previous model. The standard starter arrangement is however somewhat modified with a long flat end-tag, and then only three small tags connected to the first cartridge link. No markings have been observed on starter segments. The delivery to combat units of new and empty belts was done in the wooden transport crate “Gurtkasten 17 n.A” which contains 4 belts, each composed of a 500-round segment. This crate also contains loose starter segments and the tools required to connect or disconnect links and starters.
The “Gurt 17/81”
In 1938, the adoption of the Mauser designed MG 81 provided the Luftwaffe with a 7.92x57mm belt-fed machine gun exhibiting an enhanced rate of fire compared to that of both MG 15 and MG 17. The MG 81 could be installed either in fixed or flexible mounts. The latter configuration required the use of cartridge belts with great flexibility in the three axes. This was needed first for a reliable feeding of a loaded belt along the articulated feed lanes, which are deformed during the aiming of the weapon. Second, the empty belt must also be transferred along the exit lanes, which, for example with the MG 81Z twin mount, are particularly winding. A new multi-purpose belt denoted “Gurt 17/81” was then adopted which enabled the feeding of both the MG 17 and the MG 81. These links are described in the patent no. 738 582 applied for by the company Ruberg & Renner in Berlin on July 13, 1940 and made public on July 15, 1943. This patent claims the design of individual, single-piece, links, one side being fitted with a hook and the other side fitted with an eye, therefore allowing the interconnection of the links with one another.
One of the model of “Gurt 17/81” described in the patent was furthermore intended to enable either a permanent connection between links (non-disintegrating belt) or on the contrary a disintegrating belt where each individual link can separate from each other as soon as the cartridge is removed. A third official configuration is the so-called semi-disintegrating belt with the use of a single disintegrating link between two non-disintegrating belt sections (for example 50-round long). This was probably aimed at making easier both the handling of the cartridge belts when loading the aircraft and the transferring of the empty belt section along the exhaust lanes and recovery tanks.
The basic feature of the reversible modification disintegrating/non-disintegrating is well described on the patent illustration. The hook of the link is split in its middle with bulges at its extremity, which reduce the width of the slot. The eye is divided in its middle with a strut the dimension of which is adapted to the main slot in the hook. Therefore, depending upon the space left between the bulges at the extremity of the hook, it allows or prevents the extraction of the strut through the slot.
Official regulations indicate that the tool needed for spreading or the narrowing of these bulges, resulting in either a disintegrating or non-disintegrating link, is to be conducted with the “Gurtzange 17/81” (literally belt pliers 17/81).
Since although the hook-split had been spread, jams could sometimes occur in detaching the hook out of the strut situated in the eye. In order to guarantee a perfect separation, a second variant has been described in the patent without the strut in the eye. This variant was probably dedicated to make a disintegrating connection on the side of the undivided eye whatever the adjacent link type. This second model however remains fitted with a split hook with end-bulges that allows it to make a non-disintegrating connection with an adjacent link of the first type.
The delivery to combat units of new and empty belts was done in the wooden transport crate “Versandkasten für Gurt17/81” which contains 12 belts, each composed of a 500-round segment initially in the non-disintegrating configuration. Two rolled-up belts are put on a tray and six of these trays inserted into the transport crate.
So far, six different variations of the Gurt 17/81 have been observed from specimens by the author.
The first two initial designs of the “Gurt 17/81” as described in the patent have both been observed. These two early variants have no markings inside the links.
The second design-model has an undivided eye and a hook with a straight split without bulges. Although no official documents have been recovered, it seems that this model was produced in order to ensure a disintegrating connection whatever type of the right or left adjacent link is used. Those links of the second design-model are marked on the outer surface with the manufacturer code and inside the link marked with the number “2”.
The third design-model is probably the one that is most rarely encountered. So far, only very corroded, dug-out specimens have been observed by the author. This design is characterized by the addition of a small metal sheet inside the link that prevents the disintegration of two adjacent links during the firing. Separation of the belt remains nevertheless possible by hands according to the elasticity of the inner metal sheet. The reconnection of links seems very unlikely because of the shape of the inner sleeve. This design appears delicate to manufacture and probably fragile in use. It is presumed that this design was only fielded for test purpose and quickly withdrawn from service. Those links of the third design-model are unmarked on the outer surface and inside are marked with the number “3”.
The fourth design-model seems geometrically similar to the second model but shows a different marking arrangement. The outer surface is marked with the manufacturer’s code as well as a letter that corresponds to the month of manufacture. An instruction dated September 22, 1942 of the Reichsluftfahrtministerium indicated that from October 1, 1942 onward, links for air force use should be marked with a letter code to indicate the month of manufacture. The first letter used for this purpose was the letter “A” corresponding to October 1942. Letters were then used consecutively in the alphabetical order for the following months. Inside the link, the number “4” is impressed.
Within the fourth design-model family, a more simplified model has been observed. It is composed of an eye without a strut and a solid hook. This configuration allows only the assembly of a disintegrating belt. This design remains compatible with all previous models but the first model since that has a divided eye. The links are marked on the outside with the manufacturer’s code and a letter for the month of production. The links remain marked inside with the number “4”. According to the observation of the production-month letter-codes, it appears that both fourth design-model with split hook and solid hook have been manufactured simultaneously at least until the beginning of 1943. Since about the middle of 1943, only the variant with solid hook has been observed which seems to be the design used until the end of the war.
Since the feeding of the MG 17 requires a starter segment, a dedicated model was designed and adopted under the designation “Gurtende 17/81” (belt-end 17/81). This piece is composed of flat tags connected to one another with connecting pins similar to those used with “Gurt 17 n.A.” belts.
Two different variants of this starter segment have been observed. The earlier one is fitted on the right end with a split hook that allows the connection into the eye of any type of link situated at the left-end of the belt and therefore enables the right-hand feeding of the MG 17. The left extremity of the starter-segment is equipped with an open eye to engage the hook of any type of link situated at the right-end of the belt, therefore enabling the left-hand feeding of MG17. The second and later variant only differs from the previous by the use of a solid hook, which could engage only links with undivided eyes. Observed “Gurtende 17/81” starters are unmarked. In the case of the MG 81, the ammunition feeding occurs with the feed-cover open and therefore a starter segment is not required.
Ammunition Belting Sequences
According to the different gun installations and the specific fighting missions to be carried out, some typical ammunition belting sequences have been officially published in the Luftwaffe instruction manual L.Dv. 4000/10 “Munitionsvorschrift für Fliegerbordwaffen” (Instructions for airborne weapon ammunitions.) In the June 1942 dated issue, the belting for MG17 guns installed in fighter airplanes for air-to-air combat is composed of high-velocity ammunition. These rounds, denoted by the suffix “-v” (verbessert = improved) are loaded with a special Nitropenta tubular powder which allows an initial velocity of ~900m/s (instead of ~800m/s for standard ammunition). These high-velocity rounds can be identified by the green ring on the projectile and were officially exclusively limited for use in the MG 17. The belting sequence prescribed is:
- 5x SmK-v (armor-piercing high-velocity with green ring on projectile and red primer annulus),
- 4x PmK-v (armor-piercing incendiary high-velocity with green ring on projectile and black primer annulus),
- 1x B-v (observation explosive high-velocity with green ring on the projectile which is blackened on its lower half, black primer annulus).
- Finally, to alert the pilot that the belt is almost at its end, a sequence of 10 consecutive tracers SmK L’Spur is inserted before the last 50 rounds.
- MG17 guns used for ground attack as well as MG 81 in both mobile turret or gun pod, have a somewhat different prescribed belting sequence:
- 2x SmK (armor-piercing with red primer annulus),
- 2x SmK L’Spur 100/600 (armor-piercing tracer, illuminating from 100 to 600m, with black tip bullet and red primer annulus)
- 2x PmK (armor-piercing incendiary with black primer annulus) or 2x B (observation explosive with blackened lower part of the bullet) when attack against 4-engine bombers.
The early original “Gurt 17” and later renamed “Gurt 17 a.A.” (alte Art = old model), seen so far by the author are unmarked. The surface coating shows a gloss black finish.
The “Gurt 17 n.A.” (neue Art = new model), have on the outer surface abbreviations which clearly identify the manufacturer and which indicate manufacture before 1940. The surface coating is dark gray phosphate. Markings noted so far by the author are: R (in a circle) – B and B (in a circle) – Z – Br and Br (in a circle) – Dr.B (in a circle).
The “Gurt 17/81” of the first model are relatively scarce and only a few markings have been noted by the author. These highlight two different periods of manufacture:
- R (in a circle) – manufactured before 1940, – cr -fnh- dwc – manufactured after 1940.
- The “Gurt 17/81” of the first model without divided eye have been noted with: R (in a circle) – ayg – dwc – fnh-eek.
- The “Gurt 17/81” of the second model have been noted with: R (in a circle) – cr – acw – ayg – dwc – dw.c – fel – fnh. These links are marked inside with the number “2”.
- The “Gurt 17/81” of the third model have only been observed unmarked. These links are marked inside with the number “3”.
- The “Gurt 17/81” of the fourth model have, besides the manufacturer’s code, an additional date letter-code. Manufacturers codes noted for variant with split hook are: cr – acw – fel. These links are marked inside with the number “4”.
- Manufacturers codes noted for variant with solid hook are: acw – ayg – dwc – eek – fnh.
An unusual marking with “R” only has been examined. This might correspond to the date letter-code (March 1944) whereas the manufacturer code had been omitted. Date letter-code has been noted at least up to the letter “S” (April 1944).
All of these links are marked inside with the number “4”.
Rh-B W79V5, “Bedienung und Behandlungsanleitung zum Flugzeugmaschinengewehr ST6”, Berlin, 1937
D. (Luft) T. 6081, “MG 81 Waffen-Handbuch”, Berlin, 1941
L.Dv. 4000/10 “Munitionsvorschrift für Fliegerbordwaffen”, Berlin 1942
Chinn G., “The Machine Gun”, Bureau of Ordnance, Dept. of the Navy, Washington DC, USA, 1951
Schliephake H., “Flugzeugbewaffnung”, Motorbuch Verlag, Stuttgart, Germany, 1977
This study is respectfully dedicated to the memory of the late H.J. Woodend of Great Britain, who made the honor to the author to share his huge knowledge about belts and links and transmitted his passion for that subject.
Special thanks are also due to individuals who provided key information from their collections or archives: C.F. Kooger – the Netherlands; R. Kährä – Finland and J.B. Anderhub – Germany.
|This article first appeared in Small Arms Review V8N2 (November 2004)