The 7mm Dakota
By Chuck Hawks
Dakota Arms of Sturgis, South Dakota, USA manufactures a deluxe falling block single shot rifle, and several fine bolt action rifles. The late Donald Allen, who won the Distinguished Flying Cross as a USAF reconnaissance fighter pilot during the Vietnam War, founded the company. Throughout his life Mr. Allen was an avid hunter and shooter, and he became a well-known custom gunmaker. He served as the first President of the American Custom Gunmaker's Guild and, in 1986, founded Dakota Arms.
Dakota offers a line of proprietary magnum hunting cartridges designed by Don Allen and based on the .404 Jeffery case shortened to function in standard (.30-06) length actions. These come in 7mm, .300, .330, and .375 calibers. There are also two long (.375 H&H length) Dakota magnum cartridges, a .416 and a .450. Factory loaded ammunition for all of these is supplied only by Dakota.
This article is about the 7mm Dakota. As might be expected, the 7mm Dakota uses standard .284" diameter bullets. The 7mm Dakota is based on a rimless, bottleneck case with a rim diameter of .545"; the case diameter at the head is also .545". The case tapers to a diameter at the base of the shoulder of .531". The case is 2.50" long and has a sharp 30-degree shoulder. The cartridge overall length is 3.33".
Because the 7mm Dakota has a larger rim diameter than the standard belted magnum cartridges, it requires a bolt specially manufactured or modified to match. No doubt this will continue to limit the popularity of the 7mm Dakota.
Due to its fatter diameter the 7mm Dakota has about 15% greater case capacity than a standard belted magnum case of the same shape and length. This greater case capacity allows velocities higher than can be attained by the standard length 7mm belted magnums such as the 7mm Remington.
According to the Dakota web site, 7mm Dakota factory loads are currently offered with a 140 grain and two 160 grain bullets. The 140 grain and one of the 160 grain bullets are Swift A-Frames; the other 160 grain bullet is a CT Fail Safe. The 2003 MSRP of these .300 Dakota factory loads is about $68-$72 per box of 20. Dakota also offers unfired 7mm brass to reloaders, priced at $175/100 cases.
The 140 grain bullet has an advertised muzzle velocity (MV) of 3400 fps and muzzle energy (ME) of 3593 ft. lbs. The trajectory of that load should look like this: +2.3" at 100 yards, +2.9" at 150 yards, +2.6" at 200 yards, +1.1" at 250 yards, -1.6" at 300 yards, and -5.6" at 350 yards. The maximum point blank range (MPBR) of this load is 319 yards, +/- 3". This is an excellent long range load for hunting medium size (CXP2 class) big game.
The 160 grain bullets have an advertised MV of 3200 fps and ME of 3637 ft. lbs. The trajectory of the 160 grain A-Frame bullet should look like this: +2.4" at 100 yards, +3" at 150 yards, +2.4" at 200 yards, +0.8" at 250 yards, -2.1" at 300 yards, and -6.2" at 350 yards. The maximum point blank range (MPBR) of this load is 313 yards, +/- 3". This should be a fine long range load for large (CXP3 class) game.
The handloader has many more bullet choices, of course. Projectiles from 100 to 175 grains are commonly available, but for a case the size of the 7mm Dakota the 139-140, 150-160 and 175 grain bullets probably make the most sense. The most popular bullets are the 150-162 grain spitzers, always a good choice for any 7mm Magnum cartridge. Slow burning powders work best with these bullets in the 7mm Dakota.
The Sixth Edition of the Hornady Handbook of Cartridge Reloading shows 7mm Dakota loads for their various 154 grain bullets at MV's from 2700 fps to 3200 fps with a number of powders. IMR 7828 seems like a reasonable choice for the 7mm Dakota. 66.7 grains of IMR 7828 behind a 154 grain Hornady Spire Point Interlock bullet gives a MV of 2700 fps. A maximum charge of 76.7 grains of the same powder gives a MV of 3200 fps and a ME of 3501 ft. lbs. with the 154 grain bullet. The trajectory of that load looks like this: +2.4" at 100 yards, +3" at 150 yards, +2.4" at 200 yards, +0.7" at 250 yards, -2.1" at 300 yards, and -6.3" at 350 yards. The MPBR (+/- 3") of that load is 311 yards. It should be an excellent all-around load for a 7mm Dakota rifle. These Hornady loads used Dakota cases and Federal 215 primers and were chronographed in the 25" barrel of a Dakota 76 rifle.
The price you pay for the performance of any 7mm Magnum rifle is recoil. In the case of a 160 grain bullet fired at a MV of 3200 fps from an 8.5 pound rifle, the recoil energy is about 24.8 ft. lbs., well above the 20 ft. lbs. the average shooter can tolerate.
The 7mm Dakota's other disadvantages, in addition to its recoil, include its oversize rim diameter (requiring bolt alterations if it is to be used in standard magnum actions), the scarcity and expense of factory loaded ammunition and brass, and the scarcity and cost of Dakota rifles. Because it is fatter than ordinary belted magnum cartridges, the magazine capacity of most rifles adapted to it will be reduced by one round.
To summarize its positive attributes, the 7mm Dakota is a powerful, flat shooting, cartridge suitable for use in rifles with standard length actions. With a MPBR of approximately 311 yards (using a 150-154 grain spitzer bullet) it is well suited for hunting both CXP2 and CXP3 class game at long range. Dakota rifles are very high quality products. And there is an excellent choice of .284" bullets available to the reloader.
Copyright 2003, 2012 by Chuck Hawks. All rights reserved.