I put a 6.5 grendel upper on a mossberg lower. Had zero issues with it besides the Take Down Pins being super tight.I doubt you'd ever get a straight answer, but I'm sure they're capable of it if they don't have someone else doing it on a marking variance.
But to answer your question, I don't know if they're doing it, or have someone else doing it for them.
Got tired of shooting big tough hogs with 5.56's and have them run (dead) 300 yds into the brush.Nice looking rifle.
Several years back, I started to build a Grendel, but didn't have the long range shots that it's capable of, so I opted for a 6.8spcII instead. I kept it for a while, deer hunted with it some and even anchored a 4 pointer with it, but sold it just before Sandy Hook to one of my buddies.