Can a daniel defense mk18 shoot subsonic ammunition?

What? Every rifle can shoot subsonic ammo. Did you mean cycle subsonic ammo?

"I mean cycle subsonic ammo"

No. Even though it uses a short gas system, subsonic 223 ammo will not cycle an AR-15 platform rifle.

However, this isn't a bad thing. The rifle itself makes quite a lot of noise when it is cycling, and if you want it quiet, you don't want it cycling automatically.

That being said, you can build or buy an AR-15 in 300 blackout that WILL cycle semi-auto, and for much less than the DD's $1750 price tag.

I mean cycle subsonic ammo

Shoot yes, cycle no.