Isn't it always the case that we get beat by our own gun when we lend it out

It never fails.
There is absolutely NOTHING wrong with a 300WM for shooting these type of matches. Lots of people are looking for the most ballistic superior cartridge/bullet combination and often do not spend enough time focusing on wind reading.
Coaching is fun and frustrating at the same time. Shooter/coach dynamics come into play and some shooters do not obey the coach because they think they know better and are not on the big eyes. Even with big eyes it was very difficult to see impacts at Blakely this last match given the ground was so wet. Usually mud will fly up, however this was not the case this time.
Yes, the jury is still out on which caliber is best at 2000 yards but the big 338's get my nod. Precision first then accuracy...… I always test with multiple ten shot groups at 1000 yards and lead core jacketed bullets have always come out ahead. Yes, I do shoot solids but only in calibers where lead core bullets are not an option. The length limitation to a good lead core jacketed bullet seems to be about 1.700-1.800" long. It is very difficult to draw a concentric jacket much longer given the stroke length of the machinery currently being used to make jackets. I know of one company that is working towards creating good (long) jacketed bullets in larger calibers .375 and up, however we are a long ways away from seeing any finished product. Sierra makes great bullets and the 300gr 338 shoots fantastic as well as their 350gr .375 Matchking. The 350gr Matchking at 3200fps is a great 2000 round setup. One big advantage of lead core bullets is being able to see the impact on target. The impact signature of a lead bullet is very visible where solids are very difficult to see unless the target is clean and the lighting is just right.
EJ