The 300 Remington Ultra Magnum, 300 RUM in the shortened designation, is an excellent cartridge. It's a large case with no "belt" for headspace control, and has somewhat more capacity than the 300 Weatherby Magnum. Consequently, out of an appropriate 26-inch barrel, it has a marginal velocity advantage over the Weatherby, and a somewhat greater advantage over the 300 Winchester Magnum. Of course, there are other 30-caliber magnums to compare the 300 RUM to, but the Weatherby and Winchester are the most well known.
The 300 RUM also produces excellent accuracy. I like it best with 180- and 200-grain bullets, leaning a bit toward the 200. However, some shooters like the exceptional velocity that can be had with bullets of 165 grains, or even 150 grains. In that weight range, I regretfully imagine only a terrific splash and flying flesh and tissue. I prefer the solid "thunk" that makes the knees buckle like a well-placed punch from a heavyweight boxer, rather than a horrible wound that barely reaches the vitals, or has trouble making it through if heavy bone is hit.
Recoil of the 300 RUM, as chambered in Remington's light weight 700 SPS or XCR, can be a little on the painful side if the shooter is stupid enough to shoot it from a rest while wearing nothing more than a shirt. On the hunt, with the mind focused on the game and making a good shot, recoil is hardly noticed, if at all. The point is, the cartridge would be more popular if people were less ignorant. Standing in front of a brick wall, and then bending at the waist and running into the wall head first, is not smart. Neither is running into the wall in the fully erect position. Intelligent shooters with at least a hint of sophistication do not shoot heavy recoiling rifles in practice unless they take measures to protect their body, eyes, and ears. The 300 RUM has a reputation for coming back with considerable force, in part because most of the rifles it is chambered in are fairly light, and this has hurt sales. In contrast, the stock design of the Weatherby Mark V has a reputation for helping to reduce some of the split-second effect of recoil. Besides, the average Weatherby weighs a little more than the average Remington, which further reduces felt recoil. After trying both, in the respective rifles, I'll bet most shooters would choose a 300 Weatherby over the 300 RUM. Keep in mind, the same Remington rifles are available chambered for the 300 Winchester Magnum, which, with the available enhanced loadings of today, nip at the heals of the 300 Weatherby and 300 RUM in performance and recoil. People buy 'em right and left, so part of the problem with the 300 RUM is probably mental. Ultra Magnum. Magnum is a bad enough word to scare the hell out of some people. If "Ultra" was needed, wouldn't it have been okay to call it the "Ultra-Long Range" (ULR)? I'd like to be King for a Week at Remington, so I could systematically can some of the marketing staff.
I like things to be product related when possible, most of the time, so I like the idea of the 300 RUM being chambered in a Remington rifle. I found the best way to do this was through the Remington Custom Shop. Some years ago I ordered a pair of 700 Custom Safari Classics (no longer offered) with the same heavy-diameter barrel as used on the 375 H&H through 458 Winchester Magnum, but with no sights and in 26-inch rather than 24-inch barrel. A bit on the hefty side, but these dandies shoot like varmint rifles. The ideal scope choice was Leopold's 4.5-14x40mm LR (side focus) with RE reticle, in gloss to best match the rifle. Beautiful.
I recommend the 300 RUM for people wanting a very powerful 30-caliber rifle at a very reasonable price. Just remember what is written here about the recoil. You don't need to be in an all-fired rush to send the rifle off to get a muzzle brake installed. Instead, keep practice moderate and protect yourself accordingly. And remember this... anyone possessing a heavy-recoiling firearm must never think that it is a worthwhile gag to put it into the hands of an unsuspecting shooter just to see their reaction. I recently saw a man on the the internet do that with his girlfriend. There's a guy that needs a good thrashing. Behave, and be responsible.