Both the 300 Wby and 300 RUM have about the same power, with the RUM having the edge by a little, but individual loads will vary more than that difference. Same rim size, but the Wby is a belted magnum, so the case is a bit thinner than the RUM. Headspacing on the shoulder and having a straight, fat case makes the 300 RUM the more accurate design, but the high quality of 300 Wby ammo and guaranteed accuracy of Weatherby rifles make it a potentially better contender for accuracy. The Weatherby's case and throat design make it particularly more efficient than the 300 RUM, and the overall shape seems more conducive to feeding. Rifle and choices are another issue. Far as I know, the 300 RUM is the round more commonly chambered in new rifles, with Weatherby being the only one to chamber for the 300 Wby mag. So even if the Weatherby was the better feeding round, could a more reliably feeding rifle chambered in 300 RUM make it the more practical choice if reliability was key? Here's an application - mine. I currently have a Savage 111G in 300 RUM. Savage being the name in accuracy. Also being relatively rough and less than very reliable in its feeding, and the fat, straight cased 300 RUM doesn't make matters any better. It's in a wooden stock in hunting configuration, but the most I'd trust it for is a very long range shot on a whitetail from a rested position - I'm not counting on a second shot. I's want something more rugged and reliable for taking the kind of game the 300 longest magnums were meant for. My opinion is that these long magnums are short-changed with short barrels, and that a 30" barrel would befit them where practical. Having taken a little cosmetic damage to the barrel which would hurt resale, I'm thinking my Savage in 300 RUM could do well as a customized long range bull barreled target rifle, and I could get a more reliable rifle in the same round for hunting while the Savage would be made into a single shot. But if I was rebarreling the Savage, I could just as easily do it to 300 Wby to match a different brother rifle. The tentative choices for a hunting rifle would be a Weatherby Vanguard in 300 Wby Mag and a used Winchester M70 Classic Stainless in 300 RUM, with the Weatherby being perhaps $40 less but risking a terrible stock (apparently it's luck of the draw between a better older model and a horrid newer one within the past few years.) I already have an excellent scope for it, and the Savage target rifle would get one suited more for target use on a rifle its size. So between these reasons or reasons you know and I don't, which would be a better choice for a 300 long magnum. I realize some of you may suggest a 300 Win Mag for more options, or a 30-378 Wby for more power, but this is the level of power I'm looking for at this time. If I'm not satisfied with either option I'll look to other bullet diameters for a longest magnum, but right now I'm taking a careful look at these two rounds next to each other.