From the standpoint of accuracy, every individual rifle will have a preference for a specific load, be it it a factory load or a handload. If it was me, I'd choose a factory load that produced about 3000 fps, which suggests a 180 gr bullet, although many .300 magnum advocates prefer a 200 gr slug. That said, the bullet you choose should be based on it's intended purpose, rather than on the cartridge and rifle its fired from. Define the purpose (target/hunting medium/heavy/dangerous game, short/medium/long range) then choose the best bullet for that purpose.
The practical value of accuracy is dependent upon the range to the target, the longer the range, the more accurate the shot must be, but in discussions concerning typical big game hunting, the practical value of accuracy is often overstated. While it not the best example of typical hunting conditions, what difference does MOA accuracy make if you need to make a 10 yard snapshot offhand? The offset between the scope and the centerline of the bore is more critical in that circumstance. Despite this inconvenient truth, rifle enthusiasts gain a great sense of satisfaction if they can shoot tiny groups on paper, and it allows them to go afield confidently. If accuracy alone is the point of the exercise, simply choose a good match load, but if killing a game animal is the point of the exercise, terminal performance trumps other considerations. Nosler's Trophy Grade factory ammo includes a 180 gr Accubond, but the cost of Nosler ammo is intimidating if you're used to buying Federal blue box. If you're going to be a dedicated .300 Winchester shooter, handloading will be a huge benefit.
