Case Capacity Matters: Comparing the 6.5mm Creedmoor, .260 Remington and 6.5x55 SE
By Chuck Hawks
It should be obvious that if two cartridges of the same caliber are loaded to the same maximum average pressure (MAP) with the same weight bullet, the case that holds the most powder can drive the bullet to a higher velocity. This results in more energy and a flatter trajectory downrange.
It is, for example, why the .30-06 outperforms the .308 Winchester. Not that both are not excellent all-around cartridges, but when push comes to shove the (approximately) 10% greater case capacity of the .30-06 makes it the superior performer.
The same is true when comparing the .300 Win. Mag. to the .300 Wby. Mag., or the .358 Win. to the .35 Whelen. The differences are not necessarily great, but they inevitably favor the cartridge with greater case capacity when shooting the same bullet at the same MAP.
Therefore, it should be no surprise that the 6.5mm Creedmoor is, ballistically, inherently inferior to the somewhat larger .260 Remington and the .260 is inherently inferior to the somewhat larger 6.5x55 SE, if all are chambered in modern rifles (CZ, Ruger, Sako, etc.) and loaded to the same MAP. The 6.5mm Creedmoor case is essentially a somewhat shortened version of the .260, while the 6.5x55 uses a longer, intermediate length case (between the .308 and the .30-06) with greater powder capacity than the .260.
The 6.5x55 case will hold approximately 57.9 grains of water, the .260 case will hold approximately 53.5 grains of water and the 6.5 Creedmoor case will hold approximately 52.5 grains of water. (The precise capacity of different brands of cases will vary, due to different wall thickness, etc.)
Therefore, if these three cartridges are loaded to the same MAP, the 6.5x55 will provide the highest performance, the .260 the second highest and the 6.5mm Creedmoor will finish third. This is a physical fact and beyond dispute.
It should be noted that the 6.5mm Creedmoor was designed as a match cartridge, not for hunting. Its case was shortened to allow the neck to grip very long ogive match bullets with a cartridge overall length that would allow its use in short action target rifles.
Many low information shooters incorrectly assume that successful match cartridges must also be superior hunting cartridges, which is simply not true. They are often designed with specific features for arcane reasons that do not apply to hunting cartridges and hunting rifles.
As factory loaded to SAAMI specifications, the 6.5mm Creedmoor is loaded to a MAP of 62,000 psi, the .260 is loaded to 60,000 psi and the 6.5x55 is loaded to 51,000 psi. This is per the SAAMI standards for US manufactured ammunition and explains why the 6.5mm Creedmoor can almost equal the performance of the .260 as factory loaded in the US. (The latest cartridges tend to be standardized at a higher pressure than previous cartridges in order to make them look better, by comparison, than they really are.)
Even worse for North American hunters, SAAMI seems to have an ongoing prejudice against the classic European cartridges, such as the 6.5x55mm, 7x57mm and 8x57mm, all of which are specified way below the MAP of European factory loads. Thus, as factory loaded by the major US ammo companies, the 6.5x55 lags about 100 fps behind the .260 and Creedmoor with the 140 grain bullets that are the signature load for any 6.5mm hunting cartridge. Feed the 6.5x55 hot European factory loads, such as the Norma offerings, and the 6.5x55 averages over 100 fps faster than the 6.5mm Creedmoor and .260 Rem.
Here are standard factory hunting loads using 139-143 grain bullets from Federal, Hornady, Norma, Nosler, Remington and Winchester for the 6.5mm Creedmoor, .260 Remington and 6.5x55 SE. Listed is the catalog muzzle velocity (fps) and muzzle energy (ft. lbs.) from 24" test barrels. (Not all manufacturers offer such loads for all three cartridges.)
(Bullet abbreviations: BTHP = Boat Tail Hollow Point, ELD-X = Extra Low Drag Expanding, BT = Ballistic Tip, BTSP = Boat Tail Soft Point, PT = Partition, C-L PSP = Core-Lokt Pointed Soft Point, JSP = Jacketed Soft Point, SST = Super Shock Tip, AB = Acccu-Bond, PP = Power Point)
Note the difference between the performance of Norma 6.5x55mm loads and the US 6.5x55mm loads. This difference is because Norma loads the 6.5x55 to European CIP pressure standards, which are similar to SAAMI standards for the .260 and 6.5 Creedmoor. The 6.5x55's bigger case pays off in increased performance when other factors are approximately equal.
The Creedmoor's slightly higher MAP allows it to almost (but not quite) equal the performance of the 10 year older .260 Remington. Both of these cartridges are designed to be used in short (.308 length) rifle actions. The 6.5x55 Hornady Superformance 140 grain SST load is a special case. It uses an advanced powder to allow the 6.5x55 to equal the performance of the .260 and 6.5 Creedmoor at lower pressure.
To clarify the situation, reloaders with modern rifles can, using canister powders, load all three calibers to the same MAP with the same bullets, it which case the 6.5x55 will always be first, the .260 second and the 6.5mm Creedmoor third in performance.
From the standpoint of the big game hunter, all three cartridges do the same thing and no big game animal can survive on the difference between them. There is, however, a greater choice of factory loads in 6.5x55mm than in the other two calibers, because it has been around longer and is an established hunting cartridge around the world, not just in North America.
Copyright 2017 by Chuck Hawks. All rights reserved.