I recently listened to the audiobook version of Tom Clancy’s Rainbow Six, after finishing Executive Orders. The elite, international, counter-terror force uses suppressed “MP10s,” which are clearly MP5s in 10mm, the hot new round at the time.
In real life, the FBI’s SWAT teams and Hostage Rescue Team briefly used MP5s in 10mm:
Out of a carbine barrel the 10mm round has almost as much energy as a 5.56 round, which needs more barrel to get up to speed, but the faster 5.56 round was deemed a better choice for defeating body armor.
In the novel, they use suppressed guns, which are almost silent — with no mention of special subsonic ammo. The guns also shoot a three-round burst, which has fallen out of fashion. They also use diopter sights, which are quite popular for ISSF target-shooting, where precision is far more important than speed or low-light performance.
Product placement, yes. Which helped to keep some oddities (including recoilless rifles and gyrojets) remembered. Fallout jumped on 10mm too.
Then again, for subsonic variants those heavier bullets were more suitable.
Oh, and the high caliber fashion may be back, with high-caliber intermediate rounds like .50 Beowulf or .499 LWR or 12.7x55mm this time.
The hot subsonic round right now is the 8.6mm Blackout.