Smallest 9mm can I ever ran was this one:
http://www.breachbangclear.com/gemtech-aurora/
Quiet for about a magazine full of rounds. (Then you have to replace the wipe).
Cans are getting smaller every year, the one in JW2 looks similar to one I'm supposed to get in soon. The square shape acts more like a heat sink and has a bit more volume compared to a round can (at least in theory). Haven't seen the movie yet, but very few films use real cans and if they do, it's difficult to get the sound just right.