Your shorter barrel will be stiffer than a longer barrel of the same contour, and some claim, slightly more accurate than a longer barrel. The only thing you're sacrificing with a 24" barrel versus a longer barrel is some muzzle velocity.
The reason guys are installing longer barrels on their rifles is to increase their muzzle velocity, not to enhance accuracy. Some of the large powder capacity cartridges being used for long range hunting provide higher velocity by utilizing the longer barrels. Your 300 Weatherby Mag could also likely benefit from a 26" barrel compared to your 24" barrel, but out to 800 yds, you'll still have more than enough retained velocity to ensure bullet expansion, and enough retained energy (if you select a good long range bullet), in order to reliably kill elk and mule deer at that distance.
Now all you need to do is confirm you can keep your bullet impacts at 800 yds within the vital zone of the game animal you're shooting at. If you can do that with your rifle, then all you need to do is start hunting!