The User-Friendly .24/6mm Cartridges
By Chuck Hawks
During my lifetime the 6mm tribe has become one of the larger groups of cartridges on the market. Here in North America we can now buy factory loaded ammunition for the 6mm PPC-USA, .243 Winchester, 6mm Remington, .243 WSSM, and .240 Weatherby Magnum. In Europe they have the same cartridges plus the 6x62 Freres and 6x62R. The handloader has access to all of these plus the 6mm-222, 6mm TCU, 6x45 (6mm-223), 6x47 (6mm-222 Mag.), 6mm BR Remington, 6mm International, 6mm-.284, and 6mm-06. All of these cartridges use standard .243" diameter bullets.
This is an amazing selection of cartridges for a bullet size that was represented by one (1) factory loaded cartridge, the long obsolete 6mm Lee Navy, from 1900 until the introduction of the .243 Winchester and .244 Remington galvanized the shooting world in 1955. The 6mm Lee had not exactly set the world on fire when it was introduced in 1895, even though Winchester offered sporting rifles and ammunition for the cartridge and it was adopted as service standard by the US Navy.
But things began to change after the end of World War II when wildcatters like Warren Page (then gun editor of Field and Stream magazine) and Fred Huntington (founder of RCBS) started experimenting with .24 caliber cartridges based on necked down .308 Winchester (Page) and .257 Roberts (Huntington) cases. These experiments were widely reported in the firearms press, and were eventually commercialized by Winchester as the .243 and Remington as the .244.
The .243 became an immediate commercial success, and remains one of the best selling cartridges in the world. Remington misjudged the market when they introduced the .244 and, through no fault of its own, sales languished. Things eventually got so bad that Remington took the extraordinary step of discontinuing the .244 in 1962, only to re-introduce it the next year as the 6mm Remington in the then new Model 700 rifle.
The big advantages possessed by the 6mm cartridges are that they are extremely efficient varmint cartridges, probably better for long range shooting than either the .22's or the .25's, while remaining adequate for hunting the popular medium size big game animals. The 6mm's are modest in recoil and fun to shoot, at the range or in the field. Because 6mm bullets have relatively good sectional density and ballistic coefficient, as a group the .24/6mm cartridges offer high velocity and a flat trajectory. They are also highly accurate cartridges. The combination of light recoil, high velocity, flat trajectory, and outstanding accuracy make the .24/6mm tribe easy to hit with. And cartridges that are easy to hit with bring home the gold from matches and the venison from the field.
The lightest 6mm bullets, from about 55-80 grains, are usually frangible bullets intended for varmint shooting. The 85-87 grain bullets may be intended for either varmints or medium game. The 90-115 grain bullets are intended for the medium size species of big game. In addition, specialized bullets for target shooting are produced in a variety of weights.
Bullet selection is paramount when hunting big game animals with any of the 6mm cartridges. Rapid but controlled expansion is necessary for quick kills, as the small 6mm bullet does not have adequate shocking power without substantial expansion. At the same time, the bullet must penetrate deep into the animal's vitals to strike a fatal blow. Fortunately, modern bullet design has made it possible to combine these necessary attributes.
The .243 Winchester and 6mm Remington are the best choices for the hunter who wants to combine varmint and medium size big game hunting. Both of these cartridges are very accurate, offer light recoil (in the vicinity of 10 ft. lbs. with most loads in most rifles), and flat trajectory that makes them suitable for long range shooting. These are short action cartridges, designed to function in all short action rifles that can accommodate the .308 Winchester.
In my estimation the big case .24's, including the .243 WSSM, 6mm-284, 6mm-06, 6x62, 6x62R, and .240 Weatherby, burn too much powder to be ideal varmint cartridges. But they are good long range cartridges for hunting the medium size species of big game such as deer, sheep, goats, and most antelope species. The 6x62 and 6x62R are factory loaded in Europe, and rifles are produced by Blaser. In North America, Winchester offers .243 WSSM rifles and ammunition and Weatherby offers .240 rifles and factory loaded ammunition. The 6mm-284 and 6mm-06 remain wildcats at this writing. All of these except the (fat) short action .243 WSSM and 6mm-284 wildcat are standard length cartridges designed to function in rifles with standard (.30-06) length actions.
The third group of .24/6mm cartridges are the very short (approximately .223 length) target and varmint cartridges. The best known of these is the 6mm PPC-USA, but this group also includes the 6mm-222, 6x45, 6x47, 6mm BR Remington, 6mm TCU, and 6mm International. Only the 6mm PPC is factory loaded (both in North America and Europe), but factory rifles have been produced for all of these except the 6mm-222. Remington has loaded runs of 6mm BR ammunition in the past. These are all basically target rounds, featuring extreme accuracy and moderate ballistics.
The 6mm-222, 6x45 (6mm-223) and 6x47 (6mm-222 Mag.) wildcats were all developed specifically for bench rest competition. They also make good varmint cartridges that, because their 6mm bullets have superior BC's, can out perform their .222, .223, and .222 Mag. parent cartridges at long range.
The 6mm TCU, developed by Thompson/Center for their single shot pistols and rifles, falls into the same general class. So does the 6mm International, based on a modified .250 Savage case. The 6mm-222, 6mm TCU, and 6mm International seem to be fading in popularity, while the 6x47 seems to be hanging in there. However, with the .222 Magnum discontinued in the late 1990's by Remington, it would seem that brass from which to form 6x47 cases will become increasing hard to find. This does not bode well for the future of the 6x47.
Of these 6mm wildcats, the 6x45 appears to be the most viable. It seems to have carved out a niche for itself as a bench rest cartridge. It is based on the very common .223 Remington case, and therefore a plentiful supply of brass is assured far into the future. I would not be completely surprised to see it adopted as a factory load some day as a combination target and varmint cartridge. The 6x45 can launch a 70 grain target or varmint bullet at a MV around 3200 fps and a 90 grain bullet at a MV above 2700 fps. Ballistically, the 6x45 is virtually identical to the 6mm PPC (see below).
As I write this, the 6mm PPC-USA and 6mm BR (for Bench Rest) Remington dominate the Sporter Class in bench rest shooting. These two are very similar, and offer ballistics similar to the 6x45. Both are intended for use in single shot target rifles only. Their case geometry is very unfavorable for use in repeating rifles. The 6mm PPC is the standout among the short 6mm cartridges in terms of popularity and the only one regularly factory loaded. It is based on the .220 Russian case and factory ammunition is offered by A-Square in North America and Sako in Europe. PPC brass for reloading is available from Norma and Sako.
The .24/6mm tribe has become large, versatile, and popular. Readers interested in more information about the 6mm PPC and 6mm BR, .243 Winchester, 6mm Remington, 6x62 Freres and 6x62R, .243 WSSM, and .240 Weatherby Magnum will find articles about these cartridges on the Rifle Cartridge Page.
Copyright 2002, 2013 by Chuck Hawks. All rights reserved.