I just got a aftermarket barrel for my sig p220 carry and just got a swr hem .45 suppressor. Im sure somebody on here knows what the best subsonic ammo is out there. I know almost all .45 ammo is subsonic, but what is a quality plinking round that wont fowl my suppressor to much. Very clean ammo.
Most .45 ACP ammo is subsonic except the lighter stuff (185 gr and +P). You might want to find out if HP ammo is OK through the can. If you want clean, Most of your carry type ammo especially 230 gr Gold Dot has a flash retarded powder that should be very clean burning.
Like Robo said, any good quality 230 FMJ will be subsonic. Alot of people like to run their .45 cans wet for better sound reduction. You can use a bottle cap full of water or go to Lowe's or HD and get some Ideal clear wire pulling gel, it's $6/quart.
You can find wire pulling gel in the electrical dept., it's similar to the ultra-sound gel, its just a fraction of the cost. It seems to last longer than water and some manufacturers don't recomend putting water in an aluminum can, but it's usually gone after two magazines.