Atlantic Firearms has been offering MP5SD uppers made by Omega. The Omega SD are replicas of the H&K MP5SD. It is a faithful recreation and even has the ported barrel to be used with a compatible SD suppressors. The MP5SD magic is in the ported barrel. When H&K developed the MP5SD, sub sonic ammo was not common. So they ported the barrel to vent excess gasses of super sonic ammo. Doing so reduces them to sub sonic speeds and thus making them quieter when suppressed.
Well Omega also makes something called the SD-K.
You can see in the photo above, the barrel is tucked under the handguard. It is trilugged and threaded. The Omega SDK is a full size SD upper but it has an MP5K PDW barrel. While it is not ported and wont convert super sonic ammo to sub sonic speeds, it does allow you to use almost any round pistol suppressor you have.
The barrel is threaded 1/2×28 but I found it is out of spec and was unable to screw anything on past a few turns. I did not want to force anything on it and stripe or the muzzle device. So I reached out to Silencer Shop and they sent over a Tirant 9M with trilug adapter.
Here it is compared to my Zenith MKE Z5RS.
The Tirant 9M is modular and you can shorten it into a compact version.
I said that it was loud. But that's because I had just shot the Pump Action 300blk Troy. But the @atlanticfirearms #omegaSDK is pretty cool if you want the look of an #mp5sd but don't want to buy another #suppressor this was suppressed with an @advanced_armament #tirant9m provided by @silencershop #suppresseverything #subsonicammo @sb.tactical #sbt5brace @steve_mp5 @rollerlyfe
The Omega SDK is a semi auto version of a MP5SD. It is sold as an upper receiver, but since the upper receiver is the serialized part, and it is transferred like an AR lower. You just need to buy a clipped and pin compatible lower grip and semi auto trigger pack.
Unfortunately it will not work with the Zenith line of MKE roller locks as they use a different method to prevent their MP5s from being converted to full auto. You can see the difference in lower grip frames below. Omega on the left, MKE on the right.
Here is another video shooting the Omega SDK with Tirant 9M.
At the moment Atlantic Firearms is sold out of the Omega SD uppers. I have yet to see the SDK upper listed on their website. The SD upper retails for $1799 on their website.