I know that just pointing out some other drum fed shotguns, although most semi-auto or full-auto ones can use drum mags.
Correction, most Magazine fed shotguns can have a drum
magazine. But most shotguns are tube fed, because shotgun shells are so large that magazines aren't very practical outside of military applications, where being able to swap a new mag in quickly is important.
Both of the shotguns in Brink are tube fed, with the SRM-1216 having a unique rotating tube/magazine. If you wanted to fit more ammo into the gun, you would need a longer tube as an attachment.