I'm an absolute Grendel Whore, with 5 of those mouths to feed. 2 are 18", 2 are 16", and one is 12.5". I've run the 12.5" to 850 yards, repeatably.
One 18" is a Faxon light(er) weight barrel, and it runs great. One 18" is the BA Mk12 profile barrel, and that thing is just lights-out accurate.
One 16" is the BA Mk12 profile barrel, and that thing is just lights-out accurate. Should be seeing a pattern in what I'm saying right here...
If I could only have one of my guns, ever, should it come to that, and shiit-can all the others, I'd pick up that 16" Grendel with the BA Mk12 profile barrel, and I'd forget about the rest of them. That thing will do anything I could ever ask of it, and never leave me disappointed in my choice on choosing it.
Now, if your boy is hung between 18" and 20", and he's not all wrapped around the axle on that Faxon barrel - tell him to get the Ballistic Advantage Mk12 profile Grendel barrel. He won't regret it.
My $0.02...