MSBS Grot assault rifle (Poland)

The MSBS Grot assault rifle (formerly also known as MSBS Radon modular weapon system) is an indigenous development of Polish Military Technical Academy (Wojskowa Akademia Techniczna) and Fabryka Broni „Lucznik” – Radom weapons factory. MSBS stands for “Modułowy Systema Broni Strzeleckiej” – modular small arms system. It was originally offered in to major versions – the MSBS-5.56B Radon-B bullpup assault rifle, intended for Special Forces, and the MSBS-5.56K Radon-K standard configuration rifle intended for infantry and other units. However, it was adopted in 2016 in only one version, known as MSBS GROT and produced in classic layout. Apparently, Polish army had little interest in this weapon, as its deliveries were made primarily to second-line units of Territorial Defense Forces, the Wojska Obrony Terytorialnej – WOT. Also, due to the hasty adoption, MSBS Grot rifle had a lot of teething problems during its first few years of military service, which are solved during its mass production. By the 2021, Polish Territorial Forces received about 60,000 MSBS Grot rifles, with even more still on order.


MSBS Grot assault rifle

MSBS Grot assault rifle, version with short barrel


MSBS Radon prototypes, circa 2014. The bullpup version was abandoned later.


The backbone of the MSBS Grot rifle is an inverted U-shaped receiver, made from aluminum alloy. This receiver, along with bolt group, return spring, barrel and gas system are common for both original versions of MSBS rifles, classic and bullpup, although the latter seems to be abandoned by its manufacturer. The FB Radom factory also offers a semi-automatic only version of the MSBS Grot carbine, intended for civilian sales.



MSBS Grot assault rifle

MSBS Grot assault rifle, version with standard barrel and 40mm grenade launcher


MSBS is operated using short stroke gas piston, located above the barrel, and its gas system has manual gas regulator. Barrel locking is achieved by a conventional rotary bolt with seven radial lugs that lock into the barrel extension. Ejection windows are made on both sides of the receiver, and weapon can be set up to eject to either side; this requires partial disassembly of the gun and installation of the ejection port cover on the side opposite the “active” ejection window. Non-reciprocating charging handles are located on both sides of the receiver.



semi-automatic MSBS Grot carbine

semi-automatic MSBS Grot carbine with spare short barrel


Polymer stocks are made integral with magazine and trigger unit housings (pistol grips are separate Ar15/M16-compatible parts), and were designed in two versions – standard (with side-folding, telescoping shoulder stock, in production) and bullpup (with fixed buttplate; abandoned). Both versions feature ambidextrous safety / fire mode selectors located at the top of the pistol grip, and ambidextrous magazine release buttons located in front of the trigger guard. Bolt stop release buttons are located on the underside of the stock, behind the magazine housing. Both stock versions are interchangeable and attach to receiver using cross-pins. Polymer forends also interchangeable. MSBS rifles are fed from STANAG-compatible (M16-type) magazines. Sighting equipment is installed using Picatinny rail at the top of the receiver. MSBS Grot rifles can mount proprietary knife-bayonet (above the barrel) and a specially designed 40mm grenade launcher (below the barrel)


Specification Value
Full text name MSBS Grot assault rifle (Poland)
Caliber cartridge 5.56x45 NATO, .223 Remington
Action type select-fire
Trigger type sa
Overall length, mm 900
Length, folded, mm 670
Barrel length, mm 406
Weight empty, kg 3.65
Magazine capacity, rounds 30
Cyclic rate of fire, rounds/min 700