Compared: .243 Winchester and 6mm Creedmoor
By Chuck Hawks
This is another comparison that matches an established short action cartridge (the .243 Winchester) against a more specialized new short action cartridge (the 6mm Creedmoor) of similar performance. The reason for these recent introductions is in the realm of marketing, rather than ballistic advancement.
However, from the standpoint of a consumer looking for a new hunting rifle, there is a choice to be made. Hopefully, this comparison will help make such decisions easier.
Shown approximately life size with 100 grain SP bullet. Illustration courtesy of Hornady Manufacturing, Inc.
Warren Page, the firearms editor for Field and Stream magazine in the 1950s, necked-down the .308 Winchester case immediately after its introduction to take .24 caliber bullets. He named his creation the ".240 Page Pouper," if I remember correctly. He wrote about the cartridge in his magazine columns, generating considerable reader interest.
Winchester standardized the cartridge as the .243 Winchester in 1955, promoting it as a combination varmint and deer cartridge for their short action Model 88 lever, Model 100 autoloading and Model 70 bolt action rifles. It became an immediate success and has been a best seller ever since.
The .243 is based on the .308 Winchester case necked-down to accept standard .243" (6mm) diameter bullets. It has a .473" rim diameter, .470" head diameter, 20 degree shoulder, 2.045 maximum case length and 2.71" cartridge overall length (COL). The SAAMI maximum average pressure (MAP) limit is 60,000 psi. The standard rifling twist for .243 hunting rifles is 1 turn in 10".
All of the major US ammunition companies offer .243 factory loads. There are many bullet weights available, but typical .243 varmint loads launch 55-80 grain bullets at muzzle velocities (MV) of 3926-3425 fps and typical factory loads for hunting Class 2 game drive 95-100 grain bullets at MVs of about 2960-3185 fps from a 24" barrel (Hornady catalog figures).
Reloaders can safely achieve velocities similar to the factory hunting loads. The Hornady Handbook shows .243 reloads with their 105 grain match bullets at MVs up to 3000 fps, while the Nosler Reloading Guide shows loads using their 105-107 grain match bullets at MVs up to 3044 fps. These velocities were taken in 24" test barrels.
The .243 was designed for hunting bullets and over the years it has proven to be an effective Class 2 game (deer and antelope) cartridge. Tens of thousands of new and recoil sensitive shooters have learned to hunt medium game with .243 rifles.
The .243 is offered in a very wide variety of rifles including bolt, lever, pump, autoloading and single shot types. Few, if any, cartridges are available in a greater number of rifles. The most enduring and popular models have always been bolt actions, such as the Browning X-Bolt, Remington Model 700 and Seven, Ruger M77, Savage Model 110 series and Winchester Model 70.
Shown approximately life size with 103 grain ELD-X bullet. Illustration courtesy of Hornady Manufacturing, Inc.
The 6mm Creedmoor was conceived between 2007-2010 as a wildcat named the "6mm HOLE" by John B. Snow for an Outdoor Life magazine article explaining how wildcat cartridges are developed. Unlike most wildcatters, Snow was able to enlist the help of Hornady technicians in his project. The new wildcat was subsequently standardized as a commercial cartridge by Hornady, using the commercially more acceptable monicker "6mm Creedmoor," since the new cartridge was based on the 6.5mm Creedmoor case necked-down to accept standard .243" diameter bullets.
The 6mm Creedmoor is a short action cartridge intended for use with long range match bullets. It actually shares .308 Winchester lineage with the .243, as the 6.5mm Creedmoor case is based on a necked-down .30 T/C case and the .30 T/C is based on a shortened .308 Winchester case with a sharper shoulder.
All of these cartridges, along with the .243 Win., share the .308's .473 rim diameter and .470 head diameter. The 6mm Creedmoor uses a 30 degree shoulder angle, its max case length is 1.92" and the COL is 2.8" The SAAMI MAP is 62,000 psi. The standard rifling twist for 6mm Creedmoor match rifles is 1 turn in 8". Like the .243, it is a short action cartridge that functions properly in short (.308 length) rifle actions and magazines.
The 6mm Creedmoor has found favor with Precision Rifle Series (PRS) shooters, a rather arcane long range, steel target, timed shooting competition in which AR-10 rifle actions are popular. The 6mm Creedmoor case holds about four grains less water than the .243 case, but because it is shorter, long VLD (very low drag) match bullets can be seated farther out in the case and still work through an AR-10 magazine. It is pegged to a somewhat higher MAP in order to make up for its smaller case capacity, a way to "legally cheat" on paper in cartridge performance, since all of the modern short action cartridges can actually be loaded to the same MAP in the same rifle.
The Hornady's Precision Hunter 6mm Creedmoor factory load launches a 103 grain ELD-X bullet at a MV of 3050 fps and ME of 2127 ft. lbs. The Hornady Match load achieves a MV of 2960 fps with their 108 grain ELD Match bullet. These velocities are from a 24" test barrel. Hornady is the only major manufacturer offering 6mm Creedmoor brass cases.
Since these two cartridges can both use the same .243" diameter bullets, there is no difference in cross-sectional area or sectional density. Any difference in performance comes down to a simple velocity comparison. The bullet that starts fastest will carry the most energy downrange, generate the most killing power and the flattest trajectory. Compare MVs and the ballistic comparison is done. It is as simple as that.
The problem is, at the time this is written, Hornady does not load the same bullet, or even the same weight bullets, in the two cartridges, so a comparison of factory loads is impossible. There are dozens of .243 factory loads from the other major ammunition manufacturers, but none of them offer 6mm Creedmoor factory loads. What is a struggling gun writer to do?
An online search turned-up new (October 2017) Hornady and Sierra reloading data for the 6mm Creedmoor on their respective web sites. This online reloading data appears to be temporary and may be removed after it has been added to new printings of their reloading manuals.
(The Sierra data is at https://sierrabulletsblog.com/2017/10/03/sierra-bullets-6mm6-5-creedmoor-load-data/ and the Hornady data may be found at https://press.hornady.com/assets/site/hornady/files/load-data/6mm-creedmoor-all-data.pdf)
The latest Sierra Edition V (8th printing) and Hornady Handbook (Tenth Edition) print manuals do not include 6mm Creedmoor reloads, but, like all reloading manuals, they do include .243 Winchester reloading data for Sierra and Hornady bullets of all weights. Therefore, we can compare the Hornady and Sierra online velocity data for the 6mm Creedmoor to their print data for the .243 Winchester. For hunters of Class 2 game animals, bullets weighing 95-100 grains are the most popular in 6mm cartridges, so those are the bullet weights we will compare.
.243 Winchester Velocity
The maximum loads for Hornady 95 SST and 100 grain InterLock bullets using the 10 most appropriate powders listed in the Hornady reloading manual achieve a MV of 3000 fps from a 24" barrel.
Seven of the eight most appropriate powders listed in the Sierra reloading manual for the 100 grain Sierra GameKing and Pro-Hunter bullets achieve a maximum MV of 2900 fps, while the eighth powder (H4831SC) achieves a MV of 3000 fps. These figures were taken in a 22" barrel; add approximately 60 fps for a 24" barrel, for a MV of 2960-3060 fps.
The muzzle energy (ME) of a 100 grain bullet at a MV of 3000 fps is 1998 ft. lbs.
6mm Creedmoor Velocity
The maximum loads for Hornady 95 SST and 100 grain InterLock bullets using four of the five most appropriate powders listed in the Hornady online data achieve a MV of 3150 fps, with the fifth powder (Superformance) achieving 3200 fps. Hornady 6mm Creedmoor data is for a 24" barrel.
Four of the seven most appropriate powders listed in the Sierra online data achieved a maximum MV of 3100 fps with Sierra GameKing and Pro-Hunter 100 grain bullets. Three of the seven powders (RL-16, RL-17 and RL-19) achieved a MV of 3150 fps. This data is for a 24" test barrel.
The ME of a 100 grain bullet at a MV of 3150 fps is 2203 ft. lbs.
Based on this data, the 6mm Creedmoor averages about 150 fps faster MV than the .243 Winchester with 95-100 grain hunting bullets. This seems strange, because the .243 case actually has about 4 grains greater capacity, which should translate to somewhat higher velocity.
The answer, presumably, is that the 6mm Creedmoor is being loaded to higher pressure. We know that the SAAMI MAP is 2000 psi higher for the 6mm Creedmoor and I suspect that this new reloading data for the 6mm Creedmoor is loaded at or very close to the maximum. On the other hand, the older data for the .243 Winchester is loaded to less than the 60,000 psi permitted by the SAAMI standard.
Neither Hornady nor Sierra releases pressure data, but the Hodgdon 2017 Reloading Manual does. It shows maximum velocities of 2984-3122 fps for the .243 Winchester with a 100 grain bullet at pressures between 58,100-58,700 psi, depending on the specific powders.
I suspect pressure in the 58,000 psi range is typical of published .243 Winchester reloading data. If so, it would explain the apparent performance discrepancy between the .243 and the 6mm Creedmoor.
For the Class 2 game hunter, there is probably little or no performance difference between these two cartridges, if both are loaded to the same MAP. For the reloader, based on the available published data, 6mm Creedmoor reloads can outperform .243 reloads, as explained above.
For the hunter who shoots factory loaded ammunition, the choice is clear. The .243 Winchester is on everybody's list of the 10 best selling centerfire rifle cartridges. There are dozens of .243 factory loads, in a wide variety of bullet weights and prices, from every ammunition manufacturer and .243 ammo is available wherever game is hunted. There is only one 6mm Creedmoor factory load (Hornady 103 grain ELD-X) and it is seldom encountered and premium priced. .243 brass for reloading is widely available from all manufacturers, while Hornady is the only source of 6mm Creedmoor brass.
The situation is similar in commercially manufactured hunting rifles. The .243 is one of the most popular calibers offered in hunting rifles today. Virtually every short action hunting rifle is chambered for the .243 Winchester. The choices include bolt action, lever action, pump action, autoloading and single shot rifles, both new and used. 6mm Creedmoor hunting rifles are few and far between, principally the Browning X-Bolt Hell's Canyon and Ruger American Predator.
On the other hand, the 6mm Creedmoor is uniquely suited for Precision Rifle Series competition. If this is your sport, the 6mm Creedmoor is the cartridge of choice.
Note: This article is mirrored on the Rifle Cartridge Comparisons index page.
Copyright 2017 by Chuck Hawks. All rights reserved.