In a .44Mag, I would strongly recommend the Federal Premium 300 grain HardCast (if they still make them). Not only were they accurate in my friend's .44Mag, but they also penetrated the grisle plate on a 200+ pound hog. I can personally recommend it 100% on a 300 pound hog just because I haven't seen it, but if I were a betting man, then I would say go for it.
I have used XTPs on deer and it's my favorite bullet. Specifically, I used a .480 Ruger with 325 XTPs. Great performance on a 110 pound doe at about 35 yards. I used the same loads on a small hog (under 50 pounds) but, even though it is a .480 Ruger, I still would not like using that bullet on a 300+ pound hog.
Zachary