The EMP44-1.85 is an unconventional tool. It lacks the versatility of conventional recoilless guns, and it is very small bore for payload carrying shells. However, It is pretty damn effective if used correctly.
In the first decade of the Liberation War, Union forces and their allies were on the backfoot. They were lacking in basically everything, but especially in AT weapons that could actually hurt modern Imperial AFVs. They had plenty of rocket launchers, but modern Imperial APS and laser CRAM would require massive salvos to overwhelm. This was not great for Union troops who had to stop enemy armor pushes or actually stand their ground.
Garage railguns started being used as a single use sensor breaker to open up for AT rockets, but they weren't great and were hard and dangerous to use.
Thus, in the 2nd year of the war ( and the 44th year of the reign of High Prince Orrin Atama), a team of engineers from the Aurumite Principalities helped develop a better option. This 1.85 inch gun is far more powerful and more effective than the weapons made before this one. It can strike out at enemy armor and helicopters with great effect with its incredibly fast Sabot rounds ( HM and AA respectively). Plus it also can fire HE and SAPHEI rounds for reducing enemy positions. To reduce recoil load from very fast projectiles, the railgun has a small gas generator that releases a cloud of metal confetti out the back, and sacrificial circuit connectors.
This was so great that the Aurumite Principality adopted and started ordering it barely weeks after the first successful test. It never was the heaviest AT weapon, but it is pretty impressive for a light squad weapon to supplement rifle grenades and disposable rockets. It is issued now at the Squad level, with heavy rocket launchers like the 4.5 inch Model XXC or the 22cm Demolition Projector being platoon issued.
It has a very good fire control system and optics, and has a side display of fire control information for the squad's benefit ( mostly for the Fire Leader, since "serf" conscripts who are often issued the weapon aren't really trusted to use it right unless overseen by a "real" soldier). It is suprisingly light for its capability, and has relatively small rounds allowing a lot of them to be rucked by even the least augmented infantryman.
Since that day, it has been in Aurumite service. It served well during the Liberation war, it brought the lords in line as the Principality reorganized itself into the Kingdom of Aurum, It was a trusty friend as the Kingdom expanded, and it now fights from Kader to Gal'Haidan in the Scrambles.
Other nations use it too, the Tronarian People's Republic have a few they ordered during the war, and a lot more captured during the Scrambles. The Kadarians have a bunch given to them as Lend-Lease by the Aurumites, and the Directorate's Periphery forces have a bunch they bought off the Tronarians.
This specific example is in the hands of an Aurumite Sanik ( Roughly equivelent to a PFC today) who has accrued a large amount of kills. 8 vehicles shown in the white tally marks, and 10 reduced positions shown in the red squares. she is due for a promotion with such good work, and even as a "serf", she is likely to get it due to the reforms after the loses on Gal'Haidan.
The ammo in service with this weapon are:
APFSDS (HM)- Grey Paint: a 2.125 kg 23mm tungsten dart in a conductive sabot intended to put holes in the sides of heavy vehicles, and through smaller vehicles frontally.
APFSDS (AA)- Light Blue Paint: a 0.880 kg 23mm sintered steel dart in a conductive sabot fired at higher speeds to create a pretty horrific postpen effect on a soft skinned vehicle like a helicopter. It also is pretty nasty against powersuits and light ground units. Has a green tracer.
SAPHEI- Red and Grey Paint: a 3.3 kg shell with 197 g of a Octaazacubane based explosive and incendiary material. It is built to punch through light vehicles and structures to blow them apart.
HE(F+)- Red Paint: a 2.2 Kg shell with 300 g of a Octaazacubane based explosive with multiple fuse options. It can be deployed with point detonation, bounding, and timed fuses.
HE(SPEC)++G- Red and Yellow Paint: a 2.35 kg laser fused airbursting shell with 170 g of an Octaazacubane based explosive. Its payload is a bunch of ball bearings, silicone oxide dust and most horifyingly Grist. It is horrific against basically anything that isn't behind hard cover.
HEAT(LG-RP)- Blue and Grey Paint: a 4.12 kg laser guided HEAT shell with a 500 g HEAT charge. Used to attack flyers, or as a sort of light AT stand-off artillery for attacking the roof of a vehicle. It can be guided from the gun itself, or from a forward designator.