Not an expert on elk, but I know they are hard to kill. IMO, if you are going to spend the cash on an elk trip, just add in another 600 for a bigger rifle. You are stretching the Grendel to the limits with Elk IMO.
I used to re-load but now I "hand-load".
-- Well, at least I try --
Mongoose I personally believe that the 6.5 is a bit light up front for taking on mature bull elk! I also think, that a distance of 200 yards would present a more satisfactory result, as elk don't just fall over dead when struck by your bullet.
Now over the last several decades, I have hunted elk in several states and used several calibers. Those being a 25-06, 270 Winchester (simply to light really), 7mm Rem mag, 300 Win mag, 338/06, 338 Win mag and even the .375H&H. I preferr to hunt those bull elk with a .338 Win mag and 225 grain bullet or my backup rifle, that being a .338/06 with 210 grain bullet. Those mature bull elk are very tough animals to put down and I have never put one down on the first shot and had it drop in it's tracks, never.
I have pondered and pondered on the Grendel. I personally like the caliber but IMO it only really fits the purpose it was designed for. Shooting people. I've looked at it for a windy day varmit gun. Short range deer gun. Back up target gun. etc. etc. And when it comes down to it, there are just too many superior cartridges out there to "settle" on the 6.5 Grendel. If you are purposely hunting elk with a AR platform rifle. The 338 Federal would be a better choice. Or a 260 rem. 7/mm08 , 308, or bigger. prefferably bigger. I would just hate to have that sinking feeling of knowing I just shot an animal and I didnt see it go down do to a poor Caliber choice. IMO there are just too many suitable calibers to consider this one.
" People sleep peacably in their bed at night only because rough men stand ready to do violence on their behalf " - George Orwell
I am the way I am because I watched the movies "Red Dawn" and "Tremors" at a impressionable age.
Now over the years, when younger hunters asked me about hunting big game mainly elk, I tell them that the 30-06 caliber with 180 grain bullet would be my minimum choice. I have personally seen and range the distance of a bull killed in Wyoming at 445 yards. The choice of the bullet by the hunter was a 180 grain Nosler partition.
So those of you who might have the magnum itch, remember the Old Soldier is no slouch when it comes to shooting far down range and getting the job done. These days my favorite highcountry rifle is a model 70 Winchester (old 30-06) that was wildcated into a .338/06 and the rifle with scope weighs under 7 pounds. Shooting 210 grain bullets, it is a bonified 350 yard elk killer.
I've killed 4 elk with a 6.5 BRM built by Eben Brown of Eabco from 40 to 300 yards. Its all about bullet type and shot placement.
This round is basically a 30-30 thats been necked down to 6.5 with the shoulder moved up. I use 38 grains of VV160 that pushes a 140 grain berger VLD at 2500 fps. I think this is slightly less then the Grendel. My point is that the 6.5 is fine but take a look at bullet performance. A 400 yrd shoulder shot on an elk with this round would be questionable but if its a shoulder hit you didn't do your part. Some people will flame me for using a berger which is considered a match bullet which is fine as we're all entitled to our opinions. I've killed a lot of animals with match grade bullets and I prefer the multiple wound channels when the bullet fragments.