Regrann from @schrombo - The integrally suppressed MP5SD (here my semi-auto MKE T94SD) isn’t just a MP5 with an attached suppressor...
For once the barrel is quite a bit shorter and the suppressor reaches back over the barrel and under the handguard right up to the receiver. So the suppressor has a huge volume for a cartridge like the 9x19. But that’s not even the best part. That is the part where you can shoot regular supersonic 9x19 ammo at subsonic speeds. And that’s due to holes drilled into the barrel that reduce gas pressure and keep the bullet speed below the speed of sound. Those holes bleed the pressure not out into the open (that would kinda defeat the whole suppressor setup) but straight into the suppressor - and that’s the main reason for the suppressor reaching back right up to the receiver. And therefore the suppressor needs two threaded sections - one at the rear end where it attaches to the receiver receiver and one at the front of the barrel.
So to reiterate: this isn’t just a MP5 with a suppressor but rather an integrated weapon / suppressor unit that completely does away with the need for subsonic ammo. And man, I do need to shoot this waaaay more 😉