It has been awhile since we’ve shown the MP5SD any love. So, in case you missed our piece on the TP5SD from TPM Outifitters, who makes one of the best semiautomatic MP5SD variants on the market, here’s a nine-minute video from Machine Gun Mike on YouTube. In this basic but well thought out video, Mike explains the unique characteristics of the MP5SD submachine gun that allow it to shoot any type of  9 millimeter ammunition very quietly.

Besides being blessed with a suppressor that is nearly a foot long and two inches in diameter, the SD uses a reflex-type design where the suppressor mounts close to the chamber, rather than on the end of the muzzle. This allows the barrel to be ported with a series of holes within the first two inches of barrel. As the bullet travels down the barrel, gases bleed off into the suppressor from the ports, keeping the bullet’s velocity below the approximately 1150 feet per second speed of sound. As we have discussed at length in the past, the key to shooting truly quiet suppressed weapons is subsonic ammunition.

Instead of requiring specialized ammo, the MP5SD reduces the velocity of virtually all commercial rounds, making it one of the most quiet submachine guns ever designed.