My DDM4 PDW has performed flawlessly with subs, supers, suppressed, and unsuppressed using a variety of Hornady and Fiocchi. I zeroed (at 50yds) with the lighter spring that comes installed, worked both for subs/supers, then put in the included heavier spring for shooting suppressed. Runs as you would expect any DD product to run. I've yet to try subs unsuppressed with the heavier spring, but that's not really something I need or care about. If I'm shooting subs, it would be suppressed.
It fits nicely in a GoRuck GR1 backpack without the can, but I generally tote it around in a tennis racquet bag with suppressor. Since this photo, I've moved to all Lancer mags, which have also been 100% through a couple hundred rounds. If I had more 300blk plinking ammo, I'd shoot this almost exclusively.
It's turned out to be a great purchase, and frankly, is more useful to me as a civilian than any other rifle caliber firearm I own. If you value having rifle ballistics out to useable distances in a compact, backpack portable package outside the home, then you can't go wrong with 300blk and the DDM4 PDW. DD has a well established reputation at this point, and is top shelf IMO/IME. I think Maxim has quite a ways to go before their complete guns can be compared to DD.