Help! Why are my 9mm always louder than my 300blk???

[XFrog]

I have a 8" aero precision 300blk barreled sbr with a standard carrier and spikes T2 buffer. 7" Ti f1 can with 8 tall radials with single clips and it is the one AR host I have where you hear the bolt and target smack only. My first 9mm f1 I made the same. Loud! Second 9mm f1 I used Rustys dhc baffles. Loud! Just got my octane 9 out of jail and it is louder on my scorpion and ar9. Tried many diff ammo makes also. I do not understand how people on the forums say 9mm is more quiet. Not getting it???

[Racer]

Almost all factory 9mm ammo is supersonic and the supersonic crack is loud. Have you tried any 147 grain subsonic in the 9mm cans yet?

[a_canadian]

Remington UMC 147gr leave the muzzle if my carbine at 1040fps. 18.75" barrel. Shoots accurately. Seems a good choice for suppressed use.

[ECCO Machine]

You need to run subsonic ammo, and in the case of blowback carbines, the port pop may continue to be offensive no matter what ammo or suppressor is used. The AR9 you should be able to tune for reduced port noise, but expect the Scorpion to always snap your ears.

[XFrog]

I only shoot 147 and above in 9mm. The ar9 has gas relief on the side for blow back. Maybe that is some of the noise. The scorp is just loud. No frp with the scorp but it is noticeable on the ar9 with the same can and ammo. I can only explain it in my feeble mind thatvthe scorp is just louder so it blends in with the uncoking blast.