Jeffrey: I have only used my newish 338 Federal Rifle for spring Black Bear Hunting so far.
I have had it two seasons now and have not harvested a Bear with it as yet.
I am happy with my Rifles accuracy so far and its light weight for packin over the miles in the spring high country.
My friend here in SW Montana killed a mature Bull Elk with one shot using his 338 Federal this just past season.
He relayed the yardage as around 200 yards.
Let me say this though - even though I have never done this exact thing myself - I am sure if YOU put a 210 grain Nosler Partition through an Elks heart/lung area even out at 300 yards that Elk is going to die!
You may not knock it down but it is going to die!
I have shot enough Elk with Nosler bullets to know this to be factual!
My secondary use for my Tikka T-3 in 338 Federal is to use when Hunting the fresh tracking snow conditions and pussyfooting into the bedding areas of the Elk (defined as "thick stuff"!) and getting closer shots there in their bedding areas.
My Rifle is shooting the 185 grain Federal factory TSX ammo right now.
Some more "thoughts" for your consideration.
There are (and I own some of them!) some better "LONG RANGE" Elk cartridges out there.
My main Elk Hunting partner uses a custom 338/378 Weatherby Magnum with a 30" barrel and a Shepherd scope!
I have seen him kill Elk (including a dandy 7x7 Bull!) with this Rifle at longer ranges than you mention.
His son "allegedly" killed a Bull with this rig at 950 yards!
I don't know this to be fact as I was not along on that days Hunt.
But they both allude to that being the reading on the laser rangefinder.
Once I go through all these Federal factory TSX's I have I am going to use THE Nosler 210 grain bullets for my handloads - and I will let you know what I found out with them, then.
Hold into the wind
VarmintGuy