From a practical standpoint, the 6mm or .243-caliber family of rifle cartridges is considered the bare minimum necessary to effectively kill whitetail deer.
Fast, efficient and powerful, the various 6mm cartridges have been very popular among deer hunters for more than 50 years. The secret to their effectiveness is low recoil. Because they don't punish the shooter, they are easy cartridges to shoot well, and proper shot placement is essential to making a clean kill.
Bullet selection is also very important, as is shooting the cartridge within manageable ranges. If used within their limits, they are excellent rounds for young hunters and small-framed hunters, as well as for veterans.
For deer, the .243 performs best with a sturdy bullet weighing between 90-105 grains. For best results, use ammunition tipped with premium bullets, such as a Hornady Spire Point, Nosler Partition, Sierra Boattail or Speer Grand Slam. Federal offers a variety of selections featuring these bullets. Hornady's Light Mag ammo is also excellent.
All of the 6mm cartridges perform with an adequate combination of speed and energy at the ranges most deer hunters will encounter in Arkansas. If you use a premium, well-constructed bullet and can place it into a deer's vital area, any of these three cartridges are adequate.
Without a doubt, the .243 Winchester is the king of the 6mm class. Introduced in 1955, the .243 uses the .308 Winchester constricted (necked down) to accept a .243-caliber bullet. All four of the .308 Win.-based cartridges, including the .260 Remington and 7mm-08 Remington, are renowned for superb accuracy and potent power.
The .243 has been so successful, both afield and commercially, that every major firearms manufacturer chambers rifles in this caliber. Another advantage is that .243 Win. ammo is available almost everywhere, from Wal-Mart to rural grocery stores and gas stations.
With most factory ammunition, .243 muzzle velocity is probably between 2,700-2,800 feet per second. At 2,800 fps, a 100-gr., .243-caliber bullet carries 1,741 foot-pounds of energy at the muzzle. At 100 yards, velocity is 2,576 fps (1,474 ft.-lbs). At 200 yards, velocity is 2,364 fps (1,240 ft.-lbs.), and at 300 yards velocity is 2,161 fps (1,037 ft.-lbs.).
If your rifle is zeroed in at 100 yards, the point of impact will be 3.7 inches low at 200 yards and 13.7 inches low at 300 yards.
Although the .243 has very light recoil, you can reduce recoil even more by using a semiautomatic rifle. If you fit your rifle with a muzzle brake, you can eliminate recoil almost completely. The Browning BAR Safari is available in .243 Win. with a factory muzzle brake.
Though ballistically identical to the .243 Win., the 6mm Remington suffered a near-fatal false start.
That's because Remington initially introduced the cartridge - originally called the .244 Rem. - as a varmint round and chambered rifles using a 1-in-12 twist rate for the bore rifling. This slow twist would not stabilize bullets heavier than 90 grains.
Winchester, in contrast, marketed the .243 as a deer cartridge that could be used for varmints. Its 1-in-10 twist rate was ideal for heavier bullets, so it succeeded while the .244 languished.
In 1963, Remington corrected this problem by making rifles with a 1-in-9 twist and reintroduced the cartridge as the 6mm Rem. Even though the .243 had an 8-year head start, the 6mm Rem. has gained considerable ground.
Many handloaders prefer the 6mm Rem. because it is based on the .257 Roberts case, which is derived from the 7x57 Mauser. It can hold slightly more powder than the .243, which means you can tweak a little more speed from it.
With factory ammo, the differences are too small to mention.
.240 WEATHERBY MAGNUM
If you want the maximum combination of speed and power from a .243-caliber bullet, the .240 Weatherby Magnum is the round for you. It is the most powerful of all the commercially manufactured 6mm options. Inexplicably, it is also the least popular of the Weatherby cartridges.
The downside is that the unique design of the Weatherby case is proprietary to Weatherby, and it is available only in Weatherby's most expensive rifles.
In almost all reloading manuals, the .240 Weatherby Mag. is capable of traveling 300 feet per second faster than the hottest .243 Win. load. With a muzzle velocity of 3,200 fps, a .240 Weatherby can send a 100-gr. bullet whistling along at 2,724 fps at 200 yards and 2,504 fps at 300 yards.
With a 100-yard zero, it will drop only 2.5 inches at 200 yards and only 9.7 inches at 300 yards.
The one thing that keeps the .240 Weatherby from realizing its full potential is a lack of bullets heavier than 105 grains. Because 6mm development paralleled that of the .243, most bullets tend toward the light side. However, Barnes offers a 115-gr. 6mm in its fine X and Triple Shock bullets. With the right powder, you can drive these at speeds up to 3,100 fps, which is comparable to a .25-06 Remington.
Its light recoil makes it popular among those who want dramatic performance over the .243 Win. without a significant increase in shoulder punishment.