Compared: The 6.5mm Grendel and 6.8mm Rem. SPC
By Chuck Hawks
The 6.5mm Grendel and 6.8mm Remington SPC are cartridges similar in performance that have been discussed as possible replacements for the 5.56mm NATO military cartridge. The Grendel was actually designed as a match cartridge for the AR-15 rifle platform, and it has already showed promise in that role. The SPC was designed by U.S. military shooters and armorers as a service cartridge for the M-16/M4 rifle platform that would correct the deficiencies (particularly in stopping power) of the 5.56mm NATO.
My take on the two cartridges, and there are articles about each on the Rifle Cartridge Page, was that the 6.5mm Grendel would probably be the better match cartridge. That, after all, is the purpose for which it was designed.
For possible adoption by the military, I favor the 6.8mm SPC, since actual military shooters designed it specifically for their purposes. For me, that settles the issue. The only remaining question in that regard is, are we going to adopt a cartridge the professional soldiers actually want, or (again) force another cartridge on them?
However, I had not thought much about which would make the better hunting cartridge for CXP2 game (read deer). Which brings us to the point of this comparison: to find out which is likely to make the better hunting cartridge for us recreational shooters, who are neither soldiers nor competitive target shooters.
The 6.5mm Grendel was designed as a cartridge for long range precision shooting with AR-15 type rifles. Bill Alexander of Alexander Arms developed this short, squat 6.5mm cartridge and Alexander Arms is now offering ammunition and rifles in 6.5mm Grendel caliber. Unfortunately, these are military style match/sniper rifles on the AR-15 platform, which are of limited utility to mainstream hunters and shooters.
Alexander tried a variety of calibers for his new cartridge. The .264" (6.5mm) caliber was eventually chosen due to the availability of suitable bullets (in terms of weight and length) that were compatible with the restricted length of the AR-15 magazine.
As the model for case design, Alexander chose the 6mm PPC bench rest cartridge, necked-up to accommodate standard .264" diameter bullets. Lapua engineers assisted Alexander with modifications intended to optimize the case for use with 107-130 grain bullets, which included a longer shoulder and a shorter neck, but the PPC's basic short, fat case shape was retained.
Most of the 6.5mm Grendel's case dimensions remain similar to those of the parent PPC case. Capacity is about 35 grains of water. Cartridge overall length is 2.255" and bullet diameter is .264" (6.5mm). MAP is about 42,000 psi.
The claimed muzzle velocity (MV) with 120 grain bullets is 2600 fps. Bill Alexander fired 120 grain Nosler Ballistic Tip hunting bullets at a MV of 2600 fps into blocks of ballistic gelatin 300 yards distant, with encouraging results. He reported that the Nosler bullets penetrated 18" and expanded to .51 caliber while retaining 75% of their weight. Long experience with previous 6.5mm rifle calibers has shown that a 120 grain hunting bullet at a MV of 2600 fps is satisfactory for CXP2 class game.
Alexander Arms offers 6.5mm Grendel ammunition factory loaded with 90 grain Speer TNT varmint bullets, Nosler 120 grain Ballistic Tip hunting bullets, and Lapua 123 grain Scenar match bullets. This ammunition is loaded using Lapua brass with an Alexander Arms headstamp and costs $20/box (20 rounds). Alexander Arms also offers 6.5mm Grendel reloading dies made by Lee Precision ($44/set).
6.8mm Remington SPC
The development of the 6.8mm Rem. SPC, a .270 caliber round, was instigated and driven by special forces shooters who wanted a more effective cartridge than the 5.56mm (.223) for their specific combat needs. Soldiers in the U.S. Special Operations Command initiated (on their own recognizance) development of a new cartridge designed to work in the M16 action. The 6.8mm SPC cartridge is the result of a two year cooperative effort between individuals in the 5th Special Forces Group, the Army Marksmanship Unit, and Remington.
The old .30 Remington was eventually chosen as the basic case from which the new cartridge would spring, as its rim size required only minimal modification to the M16's bolt face. Following typical modern procedure, the .30 Rem. case was shortened (to a length of 43mm), blown out, necked-down, and given a sharper shoulder and a shorter neck.
Various calibers up to .308 were tested before settling on a .277" diameter bullet, the same bullet diameter made famous by the .270 Winchester. A relatively light bullet weight of 115 grains was chosen to match the case's modest capacity. A new powder has reportedly been developed to optimize the ballistics of the cartridge. Remington introduced the new cartridge to civilian shooters in 2004 as the 6.8mm Remington SPC with an advertised MV of 2800 fps with a 115 grain bullet from a 24" test barrel.
Remington is offering four 6.8mm factory loads, all with 115 grain bullets. These include two match bullets, a Core-Lokt Ultra hunting bullet, and a Metal Case military-type bullet. The ballistic coefficient (BC) of the Remington 115 grain Open point match bullet is .340, and the BC of the Sierra MatchKing is .333. The BC of the metal case bullet is .325, and the BC of the Core-Lokt Ultra is a rather disappointing .295.
A rather surprising change in the specification of the Remington factory loaded ammunition occurred in 2006. The new Remington ballistics tables show a MV of 2625 fps for all four 115 grain bullets. The reason for this change is not mentioned nor, according to the new catalog, has the test barrel length of 24" been changed. This is a dramatic revision, as at a MV of 2800 fps the 6.8mm SPC is clearly superior to the 6.5mm Grendel in velocity and energy at hunting ranges, while at 2625 fps the advantage shifts to the Grendel, as we shall see.
I fail to understand why Remington has not offered a 100 grain varmint/predator load using their existing Pointed Soft Point bullet (SD .186, BC .252). I would think, based on Hodgdon Powder Company data, that a 100 grain bullet could be driven at a MV of about 2800 fps. This would increase the cartridge's versatility and its appeal to recreational shooters.
Typical varmint/predator bullets for .270 caliber rifles weigh 90-110 grains. Typical bullets for CXP2 class game weigh 120-140 grains. I would guess that reloaders would find bullets such as the Speer 90 grain TNT excellent for varmints and small predators at 2900-3000 fps, while the 120 grain Barnes X-Bullet at a MV of perhaps 2525 fps should be a good choice for hunting deer, antelope, sheep, and goats.
Partisans of the 6.5mm Grendel claim superior accuracy compared to the 6.8mm SPC, but fans of the 6.8mm SPC make the same claim for their favorite. The reality is that the key to superior accuracy is the shooter, not the cartridge. I figure that the two cartridges are probably pretty similar in terms of intrinsic accuracy, and both are more than sufficiently accurate for deer hunting, so accuracy will not be a factor in this comparison.
The characteristics that we will compare include velocity and energy, trajectory, sectional density (SD), bullet cross-sectional area, killing power, and recoil. We will also take a look at the availability of rifles and ammunition, as these are of critical importance to the commercial success of any new cartridge.
Since each cartridge is available factory loaded with only one hunting bullet, we will compare those loads. In the 6.5mm Grendel the big game load is a 120 grain Nosler Ballistic Tip bullet at a MV of 2600 fps. For the 6.8mm Rem. SPC we will use the revised 2006 catalog figures for the 115 grain Remington Core-Lokt Ultra bonded-core bullet, which claim a MV of 2625 fps.
Velocity and Energy
Here are the Alexander Arms velocity/energy figures for the 120 grain Ballistic Tip bullet in the 6.5mm Grendel:
Muzzle - 2600 fps/1801 ft. lbs.
And here are the revised 2006 Remington velocity/energy figures for the 6.8mm SP's 115 grain Core-Locked Ultra factory load:
Muzzle - 2625 fps/1759 ft. lbs.
Although slightly faster at the muzzle, at 200 yards the 6.8 SPC's Ultra Core-Lokt bullet is traveling 176 fps slower than the Grendel's Ballistic Tip. This is due to the Ballistic Tip's big advantage in BC (.498 compared to .295). It also accounts for the increasing disparity in energy as both bullets move down range.
At 200 yards the 6.5mm Grendel has a 248 ft. lb. advantage in kinetic energy. Neither of these cartridges is particularly powerful, but (assuming 800 ft. lbs. as the minimum theoretical energy for cleanly taking deer size game, both develop sufficient energy for the purpose at 300 yards, which is well beyond their maximum point blank range (MPBR), as we shall see next.
The 6.5mm Grendel Ballistic Tip bullet at a MV of 2600 fps has a trajectory that looks like this:
+2.8" at 100 yards, +1.1" at 200 yards, -7.5" at 300 yards. The maximum point blank range of that load (+/- 3") is 259 yards.
The 6.8mm SPC Core-Lokt Ultra bullet at a MV of 2625 fps has a trajectory that looks like this:
+2.8" at 100 yards, +0.7" at 200 yards, -9.6" at 300 yards. The maximum point blank range of that load (+/- 3") is 248 yards.
These figures were computed for a rifle with a telescopic sight mounted 1.5" over the bore. Trajectory is thus the primary limiting factor for both of these calibers as CXP2 hunting cartridges. While there is not too much difference between them, the 6.5mm Grendel does have an 11 yard advantage in MPBR. Again, the difference is due to the superior BC of the Nosler Ballistic Tip bullet.
Sectional density (SD) is important because, other things being equal (of course they usually are not), the bullet with the higher SD penetrates deepest. And to kill cleanly, the bullet must penetrate into the animal's vitals.
The 6.5mm 120 grain Nosler Ballistic Tip bullet has a sectional density of .246.
The 6.8mm 115 grain Remington Core-Lokt Ultra bullet has a sectional density of only .214. It takes a 130 grain .270 bullet to approach the SD of a 120 grain 6.5mm bullet.
Both SD figures are adequate for CXP2 game, where extreme penetration is seldom required. SDs as low as .205 are usually considered satisfactory and SDs of around .225 ideal. Undeniably, however, the 6.5mm bullet has the advantage in sectional density.
This theoretical advantage in penetration is probably largely offset by the bonded core construction of the Remington bullet. The Core-Lokt Ultra's bonded core keeps the jacket and core together, and greater retained weight usually means deeper penetration. The Ballistic Tip is known as a "soft" bullet that tends to expand quickly and shed weight, limiting its total penetration. Such bullets do, however, tend to kill CXP2 game quickly.
Bullet Cross-sectional Area
The cross-sectional area (frontal area) of a hunting bullet matters because a fatter bullet tends to make a bigger hole in the target (other factors, like bullet expansion, being equal). The wider the wound channel the better in terms of quick kills. Here only the caliber of the bullet matters, bullet weight is not a factor.
The cross-sectional area of a 6.5mm (.264" diameter) bullet is .0547 square inch. The cross-sectional area of a 6.8mm (.277" diameter) bullet is .0603 square inch.
What the 6.8 SPC gives away in SD it regains in bullet frontal area. But, the previous comments about the respective performance of the two bullets still apply. In this case, the Ballistic Tip's reputation as a "soft" bullet works to cancel the 6.8's advantage in frontal area, since it will probably expand faster and more violently than the 6.8 SPC's controlled expansion bullet.
Killing power is the most difficult factor to estimate, as there is no scientific formula to apply. Systems have been created to estimate killing power (including one by yours truly), but none of them should be regarded as particularly reliable. And many such systems have no correlation with reality at all.
One of the better ways to estimate killing power, in my opinion, is the Optimal Game Weight (OGW) formula devised by Edward A. Matunas. It at least attempts to balance some of the major variables involved, rather than being based entirely on energy, momentum or whatever. Unfortunately for the 6.8 SPC in this comparison, the OGW formula does not include bullet cross-sectional area, the 6.8's biggest advantage. OGW does attempt to relate killing power to the live weight of game animals, a very useful notion.
For the purposes of this review, we will compare the OGW of the two calibers at the muzzle and at the maximum distance they are optimum for killing 200 pound game. (200 pounds live weight would be a large CXP2 game animal.)
The OGW figures for the 6.5mm Grendel show that cartridge optimal for 200 pound game out to about 300 yards. Its OGW at the muzzle is 380 pounds.
The Optimum Game Weight formula shows that the 6.8mm SPC should be optimal for 200 pound game out to about 165 yards. Its optimum game weight at the muzzle is 359 pounds.
Note that while the OGW at the muzzle is similar (and the difference is probably due to the formula's failure to consider bullet frontal area), down range the 6.5mm Grendel is considerably superior. This, once again, is primarily due to the vastly superior BC of the 6.5's Ballistic Tip bullet. If the 6.8 SPC were loaded with a more aerodynamic bullet, the OGW numbers would remain close.
One of the real benefits of cartridges of this approximate bore size and capacity, and one that should not be underestimated, is that they don't kick hard enough to bother most shooters. That makes precise bullet placement easier in the field, and bullet placement is the real key to killing power on big game animals.
Here are the approximate recoil energy and rifle recoil velocity numbers for both cartridges when fired in 7.5 pound rifles:
6.5mm Grendel (120 gr. at 2600 fps): Energy = 8.9 ft. lbs.; Velocity = 8.8 fps
6.8mm SPC (115 gr. at 2625 fps): Energy = 8.0 ft. lbs.; Velocity = 8.3 fps
The 6.8 SPC wins this part of the comparison with its lower recoil, although the difference is not great. The biggest advantage of both cartridges is that their recoil in a 7.5-8 pound hunting rifle should be quite low. That low recoil should endear these cartridges to the once a year deer hunter, for who either would be a good choice.
The 6.8mm SPC has the advantage of being offered by a major ammunition manufacturer with national and international distribution. This advantage should not be underestimated. It does not guarantee success (Remington has introduced other cartridges that eventually fell by the wayside), but if the 6.5mm Grendel is not picked up by a major ammunition supplier its commercial failure will be guaranteed.
No cartridge, regardless of its merits, can survive in the market place without a readily available source of ammunition. Any Remington dealer could stock 6.8 SPC ammo, and those that don't keep it in stock can order it for their customers. The 6.8 SPC a big winner in the ammo availability category.
Alexander Arms, a small business, offers complete AR-15 style autoloading rifles in 6.5mm Grendel as well as complete upper receiver assemblies for other AR-15/M16 style rifles. They call one of their AR-15 clones the "hunter" model. It is supplied with a 19.5" barrel and a flat-top receiver and carries a MSRP of $1369. As far as I can determine, that is it for 6.5mm Grendel hunting rifles.
The 6.8mm SPC is offered by Remington in three versions of their Model Seven bolt action rifle, and one version of the Model 700 bolt action rifle. A couple of these are plain blue/synthetic models, one is a stainless/synthetic model, one is a youth model, and one (the Model Seven CDL) is a deluxe blue/walnut model for the traditionalist. The shortest barrel length option is 20", and the longest is 26". These are mainstream hunting rifles with mass appeal. The average MSRP of these Remington rifles is about half the cost of an Alexander Arms Hunter Model.
In addition, complete after market "uppers" for AR-15/M16 style autoloaders are available in 6.8mm Rem. SPC. Few hunters of my acquaintance (actually none) choose to hunt deer with AR-15 clones, but if a person wants to it can be done.
As is the case with ammunition availability, rifle availability is crucial to the long term commercial success of any cartridge. If you can't find a rifle that shoots it, what good is the cartridge? Any Remington dealer, of whom there are thousands, can order a 6.8mm SPC rifle for a customer. The 6.8mm SPC wins the rifle availability part of this comparison hands down.
Summary and Conclusion
The 6.5mm Grendel dominates most performance areas of this comparison. This is somewhat misleading, however, as the critical difference is the superior BC of the 6.5's Ballistic Tip bullet compared to the 6.8's Core-Lokt Ultra bullet as factory loaded. If both cartridges were loaded with bullets of similar form, most of the 6.5's advantage would melt away.
Reloading dies are available for both cartridges, so either can be reloaded. My guess is that most fans of either cartridge are likely to be reloaders. There are plenty of 6.5mm bullets available to the reloader and even more .277" bullets, so most reloaders will likely choose to shoot bullets other than those compared here. Handloaders will be able to dramatically alter the performance results of this comparison by judicious bullet selection.
With proper bullets both the 6.5mm Grendel and 6.8mm SPC are satisfactory medium range cartridges for CXP2 game. Recoil is low, making accurate shot placement--the most important factor in killing power--relatively easy. My guess is that both will gain reputations as deadly deer calibers among those who try them simply because hunters will be able to get their shots into the vitals.
How the 6.5mm Grendel will ultimately fare against the 6.8mm SPC in the civilian market, or if either will ultimately sell well enough to become a long term success, I cannot say. If either should be selected as the new U.S. service cartridge, its success in the civilian market would likely be guaranteed.
I can say that, as things stand now, the 6.8mm Rem. SPC has a big leg-up because rifles and ammunition are being offered by a major manufacturer (Remington) and are therefore available at reasonable cost to practically everyone. Also, the Remington 6.8 SPC rifles are mainstream hunting rifles, not quasi "Army rifles." The situation could change if the 6.5mm Grendel is adopted by major rifle and ammunition manufacturers, of course, but unless that happens it is likely to remain a specialty item without broad appeal.
Copyright 2006, 2012 by Chuck Hawks. All rights reserved.