Following the lead of Winchester (with their WSM) and Remington (with their SAUM) cartridges, Hornady/Ruger have introduced the RCM line of short magnum cartridges. RCM stands for "Ruger Compact Magnum," a line of cartridges based on the .375 Ruger Magnum case shortened to allow a cartridge overall length (COL) equal to the .308 Winchester. This allows the .300 RCM to be adapted to existing short action rifles.

The new cartridge has a standard magnum rim diameter of .532". The head diameter is also .532", the case has minimal taper and the shoulder angle is 30 degrees. Case length is 2.10" and maximum COL is 2.840", slightly longer than the 2.810" COL of the .308 Win.

Like the other short action .300 Magnums, Hornady claims that the .300 RCM offers .300 Winchester Magnum performance in a shorter package when fired from a standard 24" test barrel. In addition, they also claim that, due to superior powder technology, the .300 RCM offer superior performance to the .300 Win. Mag. and the other short magnum cartridges from short barreled rifles.

For their new .300 from a SAAMI standard 24" test barrel, Hornady claims muzzle velocities (MV) of 3300 fps with a 150 grain SST bullet, 3140 fps with a 165 grain SST bullet and 3000 fps with a 180 grain SST bullet. These are comparable to the velocities claimed for most .300 Magnum cartridges from a 24" test barrel.

From a 20" test barrel, Hornady claims MV's of 3170 with a 150 grain SST bullet, 3030 fps with a 165 grain SST bullet and 2900 fps with a 180 grain SST bullet. They claim that these velocities are superior to those obtained with the .300 WSM and .300 Win. Mag. in a 20" barrel. This is probably true, but since there are no production .300 Win. Mag. or WSM rifles with 20" barrels it is a moot point.

Wayne van Zwoll, in an article published in the Jan./Feb. issue of Rifle Shooter magazine, reported chronographing some early .300 RCM ammunition from a Ruger M77 with a 20" barrel. The actual MV's with the 180 grain SST bullet varied between 2804 fps and 2847 fps.

Actually, a .300 Magnum rifle with a 20" barrel seems like the height of absurdity, which is why no one has produced such a rifle. (At least until now; Ruger is offering a M77 Hawkeye with a 20" barrel in .300 RCM.) If you want a short barrel, a standard cartridge would be a far more rational choice. Never the less, Hornady and Ruger are betting the future of their RCM cartridges on the notion that hunters will line up to buy magnum rifles with 20" barrels. Judging by Hornady's advertising for the new cartridge, it was designed from the outset to offer maximum performance from a 20" barrel. That hook is supposed to lure customers away from the other .300 Magnums.

Early reports suggest that .300 RCM recoil is comparable to that of a lightweight .30-06 rifle with a 20" barrel. Since the two cartridges have a similar powder capacity, that makes sense. What they fail to mention is that the recoil of such a .30-06 rifle is very unpleasant. They also neglect to mention that if the same powder technology were applied to the .30-06, the short barrel performance would be the same. Therefore, what the new .300 RCM really offers is a �" shorter action than a short barreled .30-06. (That, of course, is also what the .308 Win. offers.) Whether that is worth the trouble and much greater ammunition expense will be up to consumers to decide.

The .300 RCM does have a couple of advantages compared to the .300 WSM and .300 SAUM. First, it is not based on a rebated rim case, so its feeding reliability should be better. Second, because the case is smaller in diameter, some rifle magazines will be able to accommodate four, rather than three, cartridges. These considerations probably make the new .300 RCM the best of the .300 short mag tribe, particularly if applied to rifles with normal length (24") barrels. However, the .300 RCM is starting very late in the short magnum race and I wonder if it will ever be able to overcome the .300 WSM's head start.