VUP, if you are satisfied with it on your 45 then you will be very much with a 9mm. Despite the 45 cal hole, all that extra volume suppresses really well on a 9mm. Theres some youtube videos by Silencerco of sub calibers shot through the 45 Osprey and its only a few dbs louder than the dedicated caliber 9mm Osprey. 9mm is cheaper to shoot, but it can be a challenge to find 147-158 grain at times