Zenith Firearms is an importer of Turkish firearms and they are focused on selling the entire line of MKE roller- delayed blowback firearms in as many configurations as you can imagine. The roller-delayed firearms produced by MKE are actually made on behalf of H&K. MKE has a long history of being a manufacturer of H&K firearms with the only difference being that they are made in Turkey, instead of Germany.
At the last minute, Zenith Firearms decided to release their .300 Blackout Z-300 rifle. The rifle is in the same format as the Z43P, which usually comes in 5.56 NATO, but after changing some internals and the barrel, they have effectively turned the platform into a durable platform to handle the .300 Blackout.
These are available on the Zenith website right now, if you are interested in getting one for yourself.