As someone who packed an M-40a1 for over 5 years I can tell you it was because of Marine Corps Sniper School that the M40 was much of a rifle at all. The .308 caliber is really a terrible long range round; anyone who shoots any distance with a true long range round knows that. 2600 fps with a bullet that has a BC below.5 is not much of a long distance combination. It was only due to the fact our students spent 4-5 hours a day on the range for a month that they were able to do much with the 308 past 600 yards.
As far as the rifle its self, the M40 is a nice little rifle, too heavy for what it is, but a quality piece none the less.
My last three years in the Marine Corps I taught at sniper school. I tried then to get the Marine Corps to look at something other than a 308, I was partial to the big 7mm's, but even a 300 Win Mag.....anything but the 308. My thoughts fell on deaf ears, the Marine Corps was in love with the 308, primarily due to Gunny Hathcock.
It is nice to see the 338's being used now. I still like the idea of a 7mm (standard mag, stw, etc) with a 180 gr bullet around .7 bc. I know there are more hot rod rounds available but when you consider how far you will actually be shooting vs. barrel life etc, I like the 7mm.