Good times and beautiful location. Locations like that around here are unheard of. Either not possible or private land.
Keyholing at the furthest range? I'm surprised it made it that far prior to tumbling.
For reference, the projectile would have less than 889 fps (based off my loads of MORE powder and higher elevation (less dense air), so your's would be going much slower).
Energy? Wait for it. A massive 307ft-lbs. Still wouldn't want to get hit =)
I've shot 1900Y before, but it was with a 300WM. Hats off to you sir.