Why is the top silenced SMG a 9mm?

[Skribs]

I was thinking today about the MP5SD, which, to my knowledge, is pretty much the cream of the crop for stealth weaponry. I was wondering why a 9mm SMG is the top subsonic option, and why there isn't something along the lines of a UMP45 with integral suppressor (since it would be the same company).

 

[Dr.Rob]

NATO standards.

45 is pretty much a USA only thing.

 

[boricua9mm]

The 9mm is generally quieter to my ear. Being subsonic is just one factor, but powder charge and the diameter at the muzzle comes into play as well. With the .45, you've got more bang and a larger hole at the end of the can for the gasses to sneak out of.

I don't think HK cares about further development of the UMP b/c for all intents and purposes, the SMG's time has come to pass for the majority of HK's primary customer base (Mil & LE). In a world where short 5.56 carbines have displaced the SMG, why bother with the expensive R&D?

 

[dprice3844444]

9mm is supersonic until you get to the 147 grain. 45 is subsonic.you can get twice as many 9mm per pound of 45.
http://en.wikipedia.org/wiki/9×19mm_Parabellum
http://en.wikipedia.org/wiki/Speed_of_sound

 

[Skribs]

Dprice, the MP5SD is designed to reduce muzzle velocity with the normally-supersonic 9mm to bring it down to the subsonic level.

Boricua, the only reason I really see for SMGs to exist anymore over a PDW/SBR is the subsonic silenced variants for extreme quiet. I do see your point on it being harder to quiet a bigger bore.

 

[dprice3844444]

mine don't,i use a screw on can.

 

[Quiet]

A noise suppressed (Gemtech SP90) FN P-90 using subsonic (SB193) ammo is quieter than a MP-5SD.

 

[Skribs]

Yeah but how much power does a subsonic 5.7 have?

 

[Quiet]

Subsonic 5.7x28mm = Good enough for one round to take out a dog/coyote sized animal. (shot placement is key)

 

[jmorris]

9mm is supersonic until you get to the 147 grain.

115's are subsonic out of the ported barrel used in the MP5 SD, by design.