Sorry if this has been covered before.
What is the best ammo weight for this weapon.
HK Pro is pretty adamant about supersonic 115 g ammo.
But I seem to recall an article in Combat Weapons(?) that
stated that the 147 g is the ideal. Anybody?

The barrel in a SD is ported to the extent that 115gr bullets never get to supersonic speed.  147gr bullets are typically subsonic even out of 16 inch barrels.

147gr bullets function just fine in a SD, but you are sacrificing a little bit of knock-down by firing a subsonic round from a SD.

HK is pretty adamant about the 115 thing, as the barrel porting to evacuate propellant gasses prematurely is engineered to just do the job of altering the MV.
The lethality issue is the driving force behind this.
A 147gr. projectile is perfect for a suppressed conventional MP5, but if chronographed out of an SD, well, it really drops!
In the US military the SD is kinda old school. They are the coolest looking MP5,s though.
Although on base, there are pallets of 115 FMJ as far as the eye can see.
The sweet thing about the SD however, is that mofrack is ALWAYS quiet, no matter what is put through it.

So is the suppressor on an SD integral to the barrel or does it connect to the lugs?   If it is integral can one buy one for say, converting a 94 (with the proper NFA considerations)?

The barrel on an MP5SD is fastened to the receiver in an identical manner as to an MP5/HK94.
At the base of the barrel are threads. A square profile O-ring is inserted into the groove of the barrel to receiver junction to prevent the "can" from coming loose.
At the base of the barrel are 30 holes or ports.
The suppressor has two distinct chambers, the first being called an expansion chamber that traps and confines the propellant gasses exiting the ported area.
The second chamber houses the helical "baffle" setup.
The handguard area has a metal cylindrical cage welded to the receiver.
The cocking piece is also modified in that the underside is relieved to clear the suppressor.
An MP5 SD is a different animal than an MP5.
The locking piece (the arrowhead shaped part that pushes the rollerlocks out) is also different, as the weapon must function with LOWER pressure.

Quoted: The barrel on an MP5SD is fastened to the receiver in an identical manner as to an MP5/HK94. At the base of the barrel are threads. A square profile O-ring is inserted into the groove of the barrel to receiver junction to prevent the "can" from coming loose. At the base of the barrel are 30 holes or ports. The suppressor has two distinct chambers, the first being called an expansion chamber that traps and confines the propellant gasses exiting the ported area. The second chamber houses the helical "baffle" setup. The handguard area has a metal cylindrical cage welded to the receiver. The cocking piece is also modified in that the underside is relieved to clear the suppressor. An MP5 SD is a different animal than an MP5. The locking piece (the arrowhead shaped part that pushes the rollerlocks out) is also different, as the weapon must function with LOWER pressure.

Thanks ErzulisBoat for the info.  I didn't realize that they differed so much.

CZ-75Jeff,  you mentioned earlier that you were going to convert your HK94 to an SD.  Can you post what parts you had to get and what extra work you had done?

Thanks.

If you have an HK94 and want all of the SD stuff done to it without actually suppressing it, call RDTS in Arizona.
They will PERFECTLY weld a handguard cage, modify the cocking piece, thread the barrel, O-ring it, and install a dummy can.
They will refinish it PERFECTLY.
The welds are better than HK factory stuff.

Nah... I wasn't going to covert to a SD, just a regular old MP5...