OK! I know, that all gun-props in the franchise are based on real firearms (Han Solo's Mauser C96). THIS loosely reminds me of the Chinese integrally supressed Type 64.
In the recent livestream for the upcoming event in GF2: Exilium, where they showcased 2 upcoming T-dolls, one being HK416 (Klukai) and Mechty (G11), they showcased a new mini-game that'll be playable during the event in the form of a cover-based TPS similar to Nikke's gameplay.
The 3 playable units in that mini-game are Klukai, Macchiato (WA2000), and Sabrina (SPAS-12), devs had Macchiato's legacy costume and Sabrina's costumes equipped for the showcase, and had to cut the showcase short because of Sabrina's highly detailed ASSets.