Many autos probably won’t cycle subsonics, but my A400 Xtreme has cycled everything I’ve ever put through it, including 24gram two inch cartridges. My 20 gauge beretta auto however, struggles to cycle anything less than 25 grams?. It will cycle 28 gram eley hi-flyer fibre 20 gauge, which are subsonic.Odd maybe, but that’s the way it is.....
I’ll have a look out for some subsonic 12 gauge cartridges, and if I can source any locally I’ll try them in the A400 to find out.