I had an antlerless elk permit for Unit 62 in western Colorado 1st season. I shot my rifle out to 600 yds out there before the season to confirm drops. The first day was very windy, 30-50 mph according to the weather people with sleet off and on all day. Day two was just as windy but no sleet. Saw a total of one elk. Fast forward to day 4. A little after daylight I spotted a lone cow elk at about 750 yds down in the oak brush in front and to the left of me. There was no wind but I had not shot my rifle that far. The elk appeared to be in no hurry to move so I moved laterally along the ridge I was on to decrease the distance. After struggling through a couple hundred yards of oak brush on the steep slope I came to a rock slide that offered me a clear view of the elk and a place to rest my rifle. I set up my pack over a rock and ranged the elk. I got 589 yds on two consecutive readings. I dialed up my turret and watched the elk as I was still out of breath. A minute or two later a shot rang out and kicked up dirt behind the elk. It came from where I had been set up earlier. I figured I better shoot if I want to kill this elk. I was still breathing somewhat heavily and I'm pretty sure my first shot went just high. (as it turned out later, I also had dialed in an extra click of elevation). I chambered a second round and controlled my breathing. At the shot, the 300 RUM recoiled back and smacked me on the eyebrow and the elk disappeared. As I ejected the empty brass, I felt blood running down my face. Another case of magnum eyebrow! It turned out to be another member of my hunting party shooting at the elk and they were watching through a spotting scope when my shot struck the elk. They said its head lurched back and all four legs immediately collapsed. In all probability an instant kill.
I worked my way down to the elk and discovered that it was actually a bull calf. It sure looked like an adult cow to me through binocs and had the others fooled also even through a spotting scope. I had taken the elk broadside with a high shoulder shot. Both shoulders were broken, as was the spine. The 200 gr Accubond had made an exit wound about an inch in diameter. I was aiming for a center shoulder shot, but the results were devestating by this hit about 2/3 of the way up the shoulder. (Sorry for the crooked picture, camera wouldn't sit still).
My rifle is a stainless LH 700 300 RUM in a McMillan sporter stock with a Leupold Vari X III 3.5-10 with an M1 elevation turret. I had adjusted the trigger to about 2.5 lbs crisp and was shooting 200 gr AB's at 3200 fps from the 26" factory barrel. It was grouping under an inch at 100 yds and my first sighter at 300 yds struck within an inch of dead center. I don't mind the recoil as I usually use a couple of strap on shoulder pads when shooting from the bench, but the rap on the head from shooting in a field position might be a good excuse for a muzzle brake. I had planned on taking my 7 mm RUM but was having some issues with it. I was quite pleased with the performance of the 300 RUM.