GRU/AAF Next Generation Machinegun Program

Machinegun technology development

NGMG, Machinegun Program

Polymers, Alloys, Steel

Gun Milling

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Unknown

Common

This technology is used to create new heavy weapons capable of using the recently developted 10mm and 15mm rounds

As pulse capable weaponry matured, military planners predicted that these weapons would spread to heavier weapons, such as tank and aircraft cannons, missiles, and artillery. Wanting to be ahead of the curve, the GRU's Office of Military Research asked for the GRU's blessing in developing at least the beginning of these weapon systems: the crew-serviced machineguns.

The GRU already had in service a major machinegun system: the 12 mm belt fed CSW. This weapon was primarily used on vehicles as a complement to larger weapons systems, or as a means of self-defense.

Since mechanized pulse capable weapons was still a very experimental technology, the GRU OMR got away with developing two more machinegun systems, one with the 10mm and one with the 15mm. It considered toying with the 5mm, but since the program was especially for vehicular usage, it chose to omit it, since the 10mm and 15mm both had better performing caseless ammunition.

GRU OMR also received feedback from the GRU on what they would like to see in potential new machineguns. The 12mm CSW was by every definition a standard machinegun, using a single barrel and a single chamber. It was very accurate, but had a higher than wanted jam rate due to the size of the cartridge and forces involved. In addition, the weapon's fire rate was not as fast enough to effectively engage low-flying aircraft, did not sufficiently suppress targets in urban environments, and engaged groups of infantry too slowly. The 12mm CSW also required a three man team to carry, and only one to operate, which made logistical considerations more difficult. These details were crucial in the design of first machinegun.

GRU OMR set out to design a replacement weapon. Their first prototype used the 10mm caseless, and was a standard machinegun. Instead of using a belt, it used magazines holding 200 rounds. The weapon had a dual-ambidextrous magazine well located on the top of the weapon and facing out to either side. This meant that two magazines could be attached at the same time. A level aft of the well controlled which magazine fed into the weapon. If a round doesn't feed into the weapon at the end of the insertion cycle, the lever flip to the other side and allows that magazine to begin feeding. The empty magazine can then be removed from the weapon and replaced without any interruption to the firing cycle.

This weapon tackled three problems highlighted. It only required two to operate and was less prone to jamming than the belt fed 12mm CSW, and had a more acceptable fire rate. However, it caused another serious issue. Due to the higher sustained RPM, the 10mm caseless ammunition caused unacceptable overheating of the firing chamber, which housed relatively delicate mechanisms to control the magazine feed and unfired round extraction. Despite this, GRU First Directorate was happy with the program's direction, and continued its funding.

During this time, the AAF Coup happened, which led to a pause in devlopment from 15 API to 16 API. Work resumed in 17 API under the All Allied Forces Office of Military Research.

Back to the drawing board, the AAF OMR experimented with using different materials, different feed solutions, and burst firing cycles, but ultimately could not come up with an answer to fix the overheating issue without reducing the fire rate. They shelved their 10mm General Purpose Machine Gun and began designing new firing chambers.

After many disappointing trials, the AAF OMR come up with a new idea. Rotary weapons tend to deal with heat a lot better than conventional single-barrel weapons. However, they are considerably heavier and inherently inaccurate due to angular inertia. Since firing chamber heat was the problem specifically, there were no need for extra barrels, only extra firing chambers. The result was the first revolving machinegun prototype for a serious program in the history of the AAF and GRU.

The aft part of the weapon housed a revolving cylinder that held three independent firing mechanisms. If the three firing mechanisms were connected with a triangle, the corner with the firing mechanism aligned with the barrel would point downward and the other two even to the upper left and right of that point. Since the barrels are evenly spaced, the weapon is statically in the firing position, and the insertion cycle takes place half a cycle after firing. As the revolving cylinder rotates around, the bolt carrier group for each firing mechanism moves forward and back. In the static firing position, the bolt is fully forward. With the mechanism aligned with the barrel, when fired it is rotated clockwise to the next position, and the extraction of an unfired round takes place while moving to that position by moving to the full aft position before it arrives at the top left position. This specific feature was facilitated to be automatic in contrast to the SR Program. Due to the high RPM of the weapon, misfires were statistically to be more common. Automatic ejection would alleviate jams of this nature.

As the weapon rotates to the next position, the top right, the next round is inserted into the empty firing mechanism in transit. As it rotates to the top right position, the bolt carrier group begins pushing the round forward to the ready position at a constant rate. It will reach the ready position as it transits to the firing position at the bottom of the cylinder.

Due to the higher fire rate of the weapon, the conventional 200 round magazine was redesigned to be a 200 round chain fed belt holder to allow more consistent feeding of the chambers. In addition, a chain fed weapon can have multiple belt holders in series feeding into a single side of the chamber, which was determined to be useful for vehicle applications, where the possibility of only a single side of the feeder may be accessible.

The chain feed mechanism is powered by the revolving action. which drives a small gear that powers either the left or right chain drives shafts, which connect to
The design was a success and accomplished its goals. The fire rate improved to 1300 RPM and added only five extra pounds of weight, keeping the crew size to two.

The 10mm Revolving GMPG was finished in 18 API.

An upscaled version for the 15mm round, the 15mm Revolving HMG, was also created in 19 API.

Polymer, High Quality Alloys, Steel

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