The MSBS Grot (Polish: Modułowy System Broni Strzeleckiej „Grot”, English: Modular Firearm System "Grot") is a family of modular assault rifles developed and manufactured by FB "Łucznik" Radom. Early prototypes were known as the MSBS Radon.

The MSBS Grot was developed in two different configurations: MSBS Grot C (conventional design) and MSBS Grot B (bullpup design). Both configurations use the same locking mechanism, and the modular structure ensures interchangeability of parts and accessories. The MSBS Grot is intended to ultimately replace the FB Beryl as the Polish service rifle.

The MSBS-7.62N project began in late 2015, a designated marksman rifle variant based on the MSBS Grot, and was later designated as the Grot 762N.

The MSBS program was in development since 2007 by the Military University of Technology (WAT) in Warsaw with cooperation from the firearms manufacturer Fabryka Broni Radom, and was designed to replace the FB Beryl as the standard-issue service rifle of the Polish Armed Forces.

During initial tests conducted by the Military University of Technology, the MSBS-5.56 and its counterpart Heckler & Koch HK416 were subjected to comparative testing of the barrel and hand-guard for overheating during an intensive firing schedule. According to the tests, MSBS yielded the better results of the two rifles despite having a relatively light and longer barrel profile. Additional tests have also shown that MSBS is less susceptible to jamming when using lower quality ammunition or when it is insufficiently maintained, and had a more manageable recoil when fired in fully automatic compared to other assault rifles chambered in the 5.56 cartridge, such as FB Beryl, HK416, FN SCAR-L or CZ BREN 2.

One of the main design characteristics of the MSBS-5.56 is the modular weapon system. If necessary, a soldier can sacrifice, for example, one standard assault rifle to quickly repair a light machine gun during a firefight. Another feature of the MSBS Grot is barrel changeability, as found on the Steyr AUG. This means a soldier may be able to adapt their rifle based on the environment they are in, such as converting a carbine to a designated marksman rifle, in order to engage targets at a greater range. The benefits of this feature allow an infantry squad to have fewer specialised weapons. MSBS may also be used with components other than the ones manufactured domestically, and it is the first Polish rifle fully compliant with the NATO standards. The MSBS-5.56 features fully ambidextrous controls and Picatinny rail, and it may also be fed from standard STANAG magazines.

Currently, the MSBS Grot is in service with the Polish Territorial Defence Forces and is scheduled to replace the FB Beryl as the primary infantry weapon and service rifle of the Polish Armed Forces. Following the adoption of the MSBS-5.56 by the Polish military, the Grot moniker has been added to the MSBS name in honour of the Home Army commander, General Stefan "Grot" Rowecki. The literal translation of the Polish word Grot is “arrowhead” or “spearhead”.

During the 2022 Russian invasion of Ukraine 10,000 Grot C16A2s were sent to the Ukrainian military.