The .243 Winchester and its peers are more commonly known as the six millimeters, despite the fact that actual bullet
diameter is slightly larger. The .243 Winchester is a .308 Winchester (7,62x51mm Nato) necked down from 7,62mm to 6,17mm and was introduced by Winchester in 1955. Since then it has become very popular in, as well as outside Africa.
The .243 has an often related and interesting history. Both Warren Page (1910 - 1977) of Field & Stream and Fred T. Huntington (1912 - 1998) of RCBS developed 6mm cartridges at more or less the same time. Page based his design on the .308 case and designated it the .240 Page Super Pooper. Huntington used the .257 Roberts case and introduced it as the .243 Rockchucker. Winchester adopted the Page design and Remington that of Huntington. Winchester used a 1:10" (1:254mm) twist rate whereas Remington settled on 1:12” (1:305mm).
Winchester chose the tighter twist rate as it envisaged the cartridge as a small game cartridge. Remington intended its cartridge as a varminter. Hunters used both for small game. The early Winchester rifles stabilized the 90 to 105-grain bullets suited to hunting better than early Remington rifles did, and achieved success amongst game hunters.
The .243 went on to become one of the world's most popular cartridges, whereas the Remington struggled, despite being the slightly more powerful at the muzzle. The 1:254mm (1:10") rate of twist still remains the most popular for 6mm cartridges, and although some manufacturers offer a 1:228mm (1:9") there is no real reason why it should be chosen as even the 115-grain Barnes bullet was designed to stabilize in it.
The short-cased .243 Winchester naturally combines well with short actions, but not so with barrels shorter than 24.0", as its case to small bore ratio provides best performance with slower propellants. Its short powder column contributes to high accuracy potential and, since it is based on the standard rim diameter introduced with the 8x57mm Mauser, cases for it can be fashioned from virtually any popular cartridge.
Recoil is quite manageable and minimal compared to the effectiveness thereof. It is a cartridge strongly recommended for the small game hunter, the novice or females.
The .243 is an excellent penetrator with the 105-grain Speer. I am not a neck shot proponent, but have had one particularly interesting penetration related experience with such a shot from a .243 Winchester. I once fired a 123-yard neck shot at a blesbok facing me at an angle. The bullet broke its neck, but because of the acute angle of impact, it was deflected and followed the vertebrae right up to the tail, penetrating the better part of 70”.
The light 70 to 85-grain bullets perform well on varmints, but the recoil is just that tad too much to keep the object visible through the riflescope and see where the bullet strikes. Although a wide range of fourth generation expanding bullets is available in the sub 90-grain class, none of these are recommended for African hunting.
Muzzle velocities with most hunting bullet weights s hover around the 3,000 fps mark with the 115-grainer doing around 2,900 fps handloaded and the 90-grainers in the region of 3,100 fps from a 24” barrel.
Taking 3,000 fps as the average muzzle velocity its hunting bullet Green-band (2,600 fps) starts around 150 yards and terminates in the region of 300 yards, making it a savannah (150 to 300 yard) cartridge from a safari perspective. After 300 yards the cartridge runs out of steam and by the time these bullets get to the 350 yards or thereabouts mark, velocities have dropped below 2,000 fps.
The bullets being relatively light and velocities high, but not exceptionally so, it is not the best wind bucker on the market. In the hands of a hunter who can read conditions well it really is a great little cartridge well suited to game up to about blesbok and deer size.
Taking an average of 3,500 fps as a lighter varmint bullet compromise and using high ballistic coefficient bullets, velocities can still exceed 2,600 fps at 400 yards and 2,200 fps at 600 yards. Obviously that makes the .243 Winchester a plains range varminting candidate as far as a good marksman can put bullet to pelt.
For hunting out to 300 yards a variable riflescope with up to about 12x magnification constitutes a fine choice, with a 3-9x still a decent compromise. Reticules with a reasonably fine center for precise aiming on small creatures at range are the way to go.
For long range varminting a specialized varmint scope of at least 24x magnification capability is recommended.
The .243 Winchester can function with slow propellants in all bullet weights, but the dedicated user will prefer to use purpose perfect propellants.
With 105 grain plus bullets a few very slow burners such as IMR-7828 and Vihtavouri VN-165 can be tried, whereas slower-medium propellants such as Reloder-15, Norma 202, Rottweil 903 and Vihtavouri VN-140 often yield excellent results with bullets lighter than 80-grains.
The excellent straight body design of the .243 Winchester counters case head separation, but it does not stop case growth. It has a tendency to form doughnuts at the shoulder and neck junction and case care is imperative with the .243 Winchester and all its peers.
Keep neck wall thickness, overall case length and doughnut forming in check through regular attention. You would not like to see you cases come out of the chamber looking like peeled bananas.
This cartridge is a candidate for extreme accuracy measure handloading, so case batching, case uniforming and other precision handloading procedures should be considered to optimize it. Bullet seating depth variation often makes a big difference.
All handloading manuals contain reloading data, but the Lee Modern Reloading manual provides the most extensive data.
USA Relative Case Capacity
51.9 gr water RCBS Shellholder
3 Groove Diameter
.243” Bore Diameter
.237” Proof Barrel Twist
1:10” Rifling Grooves
6 x 0.68” Max Average Pressure
60,000 psi Case Trim Length