Short Magnum Facts
Here are the short magnum stats as listed in the Barnes Reloading Manual and how they compare to the standard caliber stats in the same manual.
Caliber Bullet Weight Fastest Velocity Shown
.270 Win. 130 grains 3211 f/s (59.5 gr. powder)
.270 WSM 130 3260 (74.0 gr. powder)
7mm Rem. Magnum 140 3152 (73.5 gr. powder)
7mm WSM 140 3171 (68.5 gr. powder)
.300 Win. Magnum 150 3345 (79.0 gr. powder)
.300 WSM 150 3321 (70.5 gr. powder)
.300 Win. Magnum 180 3036 (72.5 gr. powder)
.300 WSM 180 3036 (69.5 gr. powder)
As can be seen, the 270 WSM delivers only 49 more f/s but it needs 14.5 more grains of powder to achieve this.
The 7mm WSM actually beats the 7mm Rem. magnum by 19 f/s and needs 5 grains LESS powder to do so.
The .300 Win. Magnum 150 gr. bullet beats the .300 WSM 150 grainer by only 23 f/s, but requires 8.5 gr. of powder to do that.
The .300 Win. Magnum and .300 WSM tie at 3036 f/s with 180 gr. bullets, but the shorty use 3 grains less powder.
To my way of thinking, the 270 WSM (and I own one) is nowhere near as efficient as the .270 Win.
The .300 shorty, (and I own one of these) because it uses less powder than the .300 and almost matches (150 gr.) and matches (180 gr.) the bigger case .300 in velocity, is a pretty efficient round.
The 7mm WSM seems to be the most efficient, beating it's big brother in velocity and using less powder to do it. (I WISH I owned one of these!)