KPMR Type 503

コンバットポータブル マシンリピーター 503型 (Romanized: Konbattopōtaburu mashinripītā 503-gata) (Common: Combat Portable Machine Repeater Type 503) Masaki machine gun
Type	Heavy machine gun
Place of origin	Horokoshi
Service history
In service	2024 - present
Used by	Horokoshi Imperial Armed Forces
Production history
Designer	Isobe Masaki
Designed	2014-2022
Manufacturer	Yondan Heavy Industries
Produced	2023 - present
Variants	See Variants
Specifications
Weight	60 kg (empty)
Length	2150mm
Barrel length	1500mm
Cartridge	15.5x116mm
Action	Gas-operated short recoil, rotating bolt
Rate of fire	700 RPM
Muzzle velocity	1,090m/s (15.5 armor piercing ammunition)
Maximum firing range	2,000m
Feed system	Dual-feed, 2 box magazines with 70 round belts
Sights	Picatinny rail-attached iron sights or optics

The Konbattopōtaburu mashinripītā 503-gata (English: Combat Portable Machine Repeater Type 503) is a heavy machine gun designed by Isobe Masaki, produced by Yondan Heavy Industries. It is the result of ten years of prototype development for the Horokoshi Imperial Armed Forces of a machine gun that can simultaneously be fielded in place of standard 12.7x99mm machine guns and 20mm autocannons on motorized infantry and mechanized infantry platforms. Most of the prototype development was devoted to the machine gun's proprietary cartridge, 15.5x116mm, which was first tested in rechambered machine guns of foreign origin, but Yondan approved of the development of a new machine gun that would be best suited for the cartridge. The 15.5x116mm was required to perform with improved armor piercing capability against the 12.7x99mm while being a lighter weight ammunition than 20mm platforms. The Imperial Armed Forces mandated that the cartridge needs to have a muzzle energy of 35,000 joules.

Sometime in 2018, the Imperial Armed Forces Office of Project Development mandated the machine gun needs a dual-feed system to allow operators swift ammunition change from one ammunition type to another. Typically, this would be a change from standard armor piercing ammunition to anti-material high-explosive incendiary/armor-piercing ammunition.

The machine gun's final prototype was completed in October 2022, and the Office of Project Development approved testing where five models would fire 100,000 rounds. The models passed the testing criteria (no more than three major failures per 10,000 rounds), and the Chief of Staff of the Imperial Armed Forces approved the prototypes to be final production for the Imperial Armed Forces and approved of service, in October 2023.