For those of you curious why the 375 Ruger is not King it is because the 375 RUM is the real king of the hill... hail the real King...
The Real King the 375 RUM, this fellow completed a series of test with his new Rem 700 LSS and was glad to report that this round is not likely to fade away like so many of the new full length beltless Mags. It has the power of the 416 Rem and the trajectory of a 270 Win in full power configuration and is not the least bit temperamental when reloading. This includes a wide variety of reduced loads suitable for duplication of the 35 Whelen and 375 H&H. Expansion ratio is the same as the 270 Win, so it uses the same powders to shoot bullets of equal sectional density the same velocity: 4350, 4831, R19 and IMR 7828 all work very well over a good range of bullet weights. Just double the weight of any 270 bullet and you will get the velocity of the 270...a 130 gr 270 at 3000 to 3150 fps is a 260 gr 375 at the same velocities, and so on.
Rumor has it that Rem will follow the approach they used for the 416, by offering factory reduced loads once the cartridge establishes a basic market. These will be reduced pressure loads insensitive to heat and cold giving 375 H&H velocities and a slight recoil reduction below the H&H. This is an excellent marketing idea, as many, many 375 H&H rifles are sold and one would be hard pressed to pass up a 375 RUM for the same price with the same long established performance with the up side in power and range available in the same rifle. Length, magazine capacity and case head size are the same.
The handloader can, of course, make these reduced loads now, and my experience is that consistency and accuracy are excellent with XMP 5744 and IMR 4064...even at load densities of less than 60 percent. Top all around load for deer is 59 grs of XMP 5744 with a 225 gr Hornady SP at 2673 fps. The same charge will give 2430 fps from a 270 gr Hornady SP. Both of these are 35 Whelen duplication loads and have the same recoil.
To move up to a good 375 H&H load try 78 grs of IMR 4064 with the Hornady 270 SP for 2640 fps. This has the recoil of a 338 Win Mag and the authority of the H&H.
For full power loads, the best powder for 270 and 300 gr bullets was IMR 7828 and believe it or not, there is no difference in velocity between the 375 RUM and the 378 Weatherby when both rounds are loaded to the same pressure. IHe didn't give load data, because it makes NO SENSE to use max pressures in the RUM case necked to .375, because nothing is gained in any practical sense. You can safely get 5800 FP out of it in a 26 inch bbl. 5200 FP is PLENTY, and the recoil is far more manageable. Factory loads come in a a shade over 5000 and are sub-max.
He did the same type of tests with the 338 RUM, and it is also a fine round, but one is left wondering if the long action and the recoil are really worth it compared to the 338 Win Mag. One is left with the notion that the 338 RUM advantage is one of RANGE rather than power, since the smaller 338 Win will perform very well on dangerous game in close and still shoot flat enough for 300 yard opportunities.
The 375 RUM is a different proposition, as the next step down is the 375 H&H and they both come in the same rifles and action lengths. And one can still drop down to deer sized game with less overkill than a 300 Win mag. At the top end, a 300 gr partition at 2800 fps (reduced load) will take the pucker factor out of dusk in Griz country. For Africa there are a number of 350 gr 375s that will loaf along at 2600 fps with great authority.
