If you have a suppressor that matches the threads of the barrel and caliber you could use it with the Maxim Defense Industries MDX 505 Mil-Spec URG Upper Receiver.
Yes you can use a suppressor on these models but unfortunately for some reason Per Maxim and website they say that if you remove the Brake and install a suppressor it voids the whole firearm warranty, BUT what is the point of a 300 Blackout if it’s not suppressed.??? I own one and I voided that Warrenty as soon as it came home! Good luck but 300 and 762 are good suppressor rounds from this host weapon