The speed of sound is a pretty small window. To get enough energy to accomplish more than paper punching, you will have to up the weight! 147 is the military standard for sub-sonic 9mm since the Vietnam War. Accurate powder also gave sub sonic data using .357 158 grain soft points in 9mm. When I started making sub sonic loads for my MAC-10, the heaviest projectile one the open market was Sierra's 130 FMJ Tournament Master. I used WW231 with great results. For 147 & 158 grain bullets AA #2, #5, & #9 all worked pretty well. With the 130gr/WW231 load I could keep 5-6 round bursts in 3 to 4 inch groups at 50 yards fired from the shoulder stock. Without using a stock, full-auto groups are much bigger than #4 Buckshot patterns at the same distance! The heavier bullets add a little more recoil (still not much!), but always seemed to group better in carbines and sub-guns (at least for me.)
Due to the lack of energy, I quit the entire 9mm program 25 years ago and went with 45, but still not much knockdown at 50 yards. So I gave up on sub-sonic and use 223 & 308 and put up with the sonic crack. A 223 from a silenced AR-15 sounds like a high velocity 22 LR (un-silenced). Without full auto the neighbors thought I was plinking with a 22!
I have come back to 9mm for CCW, but not with a silencer. The funny thing was Before Ohio had CCW, my State Fire Marshal's "Dangerous Ordinance" permit, allowed me to CCW the machine gun and silencer!
For CCW 9mm I like the 147 grain factory ammo, and it is sub-sonic (at least in a handgun, don't know about a carbine).
Hope you figure out what you want, without spending too much time and money!
Ivan
