There is more to gain in barrel length, for such a large cartridge, than just velocity. There is internal ballistic efficiency resulting in lower ES and better accuracy. This, overall, as somebody out there probably has a 300WM shooting 1/4moa despite too short of a barrel for the cartridge. On the other hand there is probably someone out there shooting 1/4moa with a longer 300WM and this is the gun I'd choose for distance shooting.
Other than weight, I can think of no gain in a short barrel -even with smaller cartridges. Weight can be managed or planned for, and the weight may be exactly what you need in 300WM. Afterall, recoil does nothing good for accuracy.
There are folks who take the shorter-stiffer notions beyond reality for hunting cartridges. Remember, guns fall into a balance whether great or crap. The best presenting a better balance.
Consider this 27" barrel for a tiny little 6Dasher using 32gr of varget:
0.40x" at 600 Yards — Schatz Shoots Small (Amazingly Small) « Daily Bulletin
I know, I know,, it's a wallet group. But the 27" barrel length didn't hurt, and makes consideration of shorter barrels for way larger cartridges seem amiss to me.
He's added weight to that gun to make it 17lbs. An extra pound in the scope, and probably 2-3lbs in the buttstock. You may need to add weight to bring a 28"+ barreled gun into balance. But all this should be considered and accepted in cartridge choice. You chose 300WM.