6.8 SPC and more on Strategy Page

The Caliber Conflict

I think this might be a re-post of an old article, but James Dunnigan summarizes the discussion of 6.8 SPC vs. 6.5 Grendel vs. 5.56 NATO. I point it out because MO readers eat this stuff up.


  1. It’s called 6.8 ‘special purpose cartridge’ so they won’t have to sell it as a replacement for the 5.56, which is basically a non-starter position. They’ll argue that it’s just for the SF types in specific situations. Of course, once it’s adopted for that, everyone will want the whizzy SF gear. Basically if the military wants a short barreled rifle they’ll need to go to one of the new cartridges like 6.8 SPC. 5.56 X 45 is dandy as long as you’ve got enough velocity to fragment the bullet on impact with flesh, and the M4 barrel is already so short that that’s pretty sketchy. If they do adopt the carbine version of the XM-8 as the standard issue weapon the barrel will be even shorter and terminal ballistics even worse. They’ve got to (or should) make a choice: if they want a shorter rifle they’ll need a different round.

  2. You make some excellent points……however, you don’t take into account blended metal bullets (by RBCD) or Cor Bon’s DPX (or is it DXP) bullets. Both would offer substantial performance improvements in 5.56 x 45 ammunition; even when fired from weapons with shorter barrels. The same is true for other calibers as well (say……I wonder what they’d do in 7.62 x 51?) I do think you’re right about the incremental approach likely being used to get ‘another’ cliber into our inventory though.

  3. The blended metal bullets have a bad rep amongst the ballistics people, including Dr. Roberts, one of the people behind the 6.8 SPC and an acolyte of Dr. Fackler, one of the giants in the field. But it’s correct that the lethality of the 5.56 could be improved with different bullet designs. The most effective wounding mechanism of the 5.56 is fragmentation shortly after it yaws, about 10 cm into the wound. That depends on variables like the jacket thickness. The more recent 62 gr. production bullets have a fairly complicated makeup and fragmentation has been variable on a lot-to-lot basis. See http://home.snafu.de/l.moeller/military_bullet_wound_patterns.html for the mechanics of 5.56 terminal ballistics.

  4. O.K., you folks are missing the point. Even the best ‘fantasy world’ 5.56 mm round does not carry the amount of energy that we’re after here. The guys in green(myself included) want a round that will stop the enemy in his tracks. If you read the reports from all of our conflicts for the last 12-15 years, the one consistent complaint is that our round does not carry enough ‘knock-down’ power. Even with a 62 gr. blended metal bullet, the kinetic energy just does not pay off in Ft.-lbs. The goal here, is to create a round that stops the enemy, and makes him unable to fight, and heres the important part, immediately. Not after he’s run another 30 meters to cover, but right now. I understand that that’s also a marksmanship issue, and that not every ‘torso’ hit is going to hit a major organ, artery, vein, or bone. What we need is a larger bullet that imparts more energy to the target, and creates more fluid shock as it sheds the kinetic energy of it’s flight. This is not about ‘wound channels’, it’s about stopping power. KILLING POWER. I don’t want some crazy jihadist running right at me, and have to shoot him twelve times to make his adrenaline fueled, amphetamine supplemented charge stop. I want to shoot him once, maybe twice, tops. This is where the 6.8 is better than the 5.56, or the 6.5 grendel. This or a return to the 7.62×51. We need a larger diameter round for this purpose, not so that our enemies can bleed out later, but so that they drop, and they drop right now.

  5. Sorry, but I have to add this. Note how the last few conflicts we’ve been in, the enemy is all ‘hopped up’? (Somalia, Afghanistan, Iraq) In Somalia it was khat, in Afghanistan it’s dope and heroin, and in Iraq it’s adrenaline and amphetamines. These ‘masterminds’ of terror, know that our round will barely slow down someone that is all ‘cranked up’. It’s like the Phillipine insurrection. That’s where we went from the .38 pistol to the .45. We need the knockdown, and the heavier bullet to achieve it. I know people talk about combat loads, and talk about the thousands of 5.56 rounds you can carry, but I’d rather have 2/3 of the rounds, and have them be 3x more effective. If it takes an average of 3 hits to make the enemy ineffective, I’d rather carry fewer of a more effective round. Just a thought.

  6. The problem with ‘knockdown power’ is that as a concept it’s wildly unscientific. If a round has enough power to ‘knock over’ a man it has enough power to knock over the shooter, too. And even a .50 BMG isn’t going to do that. Fast incapacitation is almost entirely a matter of shot placement. If you hit the central nervous system (spine or brain) the guy goes down immediately. The less rapid way to shut someone down is through loss of blood pressure to the brain, typically by blowing out the heart or major artery. That can take 30 seconds or a minute from impact. Both of these mechanisms result from physical damage, namely the wound channel. The bigger the wound channel, the more likely it is to hit either the CNS or the heart/major artery. How that wound channel is created is largely irrelevant. Hits outside of these two areas may or may not incapacitate the enemy. It depends in part on the state of mind of the person that just got hit. Plenty of people with legs blown off have continued to fight just because they’re onery or focused, and there’s no way any small arms round is going to cause anywhere near that amount of damage. The 6.8 has some possibilities because the tested rounds can fragment like the 5.56. It’s got more energy behind it and more bullet mass when it fragments, so it can make even bigger holes. Something like 7.62 X 51 with US bullets is likely to be _less_ effective than 5.56. See the Fackler article I linked to earlier. The US 7.62 rounds tested made smaller holes than 5.56 because they stayed point-first longer and didn’t fragment. The ‘energy transfer’ idea of wound ballistics doesn’t describe actual results very well. It’s all about the holes.

  7. Mr. Blofeld(do you have a white cat?) I understand that ‘knockdown’power is much more difficult to empirically prove, however, your information that ‘wound channels’ and the science thereof will provide a 5.56mm round that will perform adequately, well, I find it unrealistic. Yes, it makes a cavity when it yaws. Yes, that usually happens in the width of a human body. Has it proven to be patently problematic at ranges over 100 yds? Once again, Yes. The point to my earlier post is that we need to go to a larger round to impart more energy to the target. My point was not that blended bullets, etc., were not still to be used, but that a larger bullet at similar velocities carries more energy. It’s simple ballistic science, not a matter of ‘voodoo’ knockdown. For instance, I hunt deer. For a period of time, I used a .243 or 30-30. I noticed that the obvious knockdown power of the 30-30 would sometimes even knock the deer over, while that almost never happened with a .243. Mind you, my longer range shots involved a little ‘kentucky windage’ with the 30-30, but it brought down the deer, and it usually brought them down faster (when it did not, it was usually my fault, bad shot, poor placement, whatever). I have since gone to a .45-70, and am extremely pleased that I never have to ‘chase down’ my deer. With a shot to the chest, it usually knocks them over, and they very seldom get up. I’ve only seen 1 deer get knocked over with a .243, and that was a shot to the head. When field dressing these deer, I got a first hand look at the damage done by these rounds, and I can promise you, the damage done by an expanding .45-70 round is far greater than any I’ve seen from a smaller round. I’m not saying that fragmenting bullets aren’t the way to go, I’m just saying if they’re larger, they’ll make a huge hole, rather than just a large one. If it makes a saucer size exit wound, so much the better. I’m not saying we need a .50 bmg for every soldier, I’m just saying a .32-.38 caliber round should be attainable, and with current recoil suppression technology, shootable, even for beginners. You’re only expected to hit a small human-size target at 300 meters. That’s certainly attainable, and will carry much more energy with a heavier round. Should it yaw and fragment in the width of a human being, certainly. Should it be able to stop said human being, most definetely. Should it rip great gaping holes in the bodies of drugged up islamo-fascists so that they can’t shoot or behead or blow anyone else up, absolutely. Please also note, that a larger round with the same yaw/tumble/fragmentation properties increases the chance of a fragment ripping an artery/vein, or organ. Wound channel science is fine and dandy, but let’s do the logical thing with it, build a better (militarily) round. One that imparts more energy(therefore larger), and makes a bigger wound channel.

  8. Oh, BTW, If you talk to most of the guys where 1 shot has to count, what round do most of them use? There are many stories from Vietnam, Somalia, Afghanistan, and Iraq showcasing the effects of the 7.62×51 versus the 5.56×45 round. The 7.62 mm round may not yaw and fragment, but from everything I’ve read it seems to have a more immediate effect. This may also be due to the ‘expert’ shooters that tend to carry the larger weapons, but I’ve gotta say it, it seems to be doing just fine. I’ll take a M1a SOCOM, thanks.

  9. Yes, ‘knockdown power’ is hard to quantify. But there’s no doubt that complaints of the lack of it have been going on since the 5.56 was adopted.

  10. Bullets make holes by several mechanisms: 1. Diameter. Bigger bullet, bigger hole. This turns out to be not that big of a deal, since 7.62 is only a couple millimeters more in diameter than 5.56. 2. Yaw. Since the center of gravity of modern bullets is towards the rear, they’ll eventually rotate when they hit a medium denser than air and travel base-first. 5.56 bullets and 6.8 SPC bullets seem to do this more quickly than 7.62 bullets, but they’ll do it eventually. 7.62 has a tendency to not rotate at all in extremity shots, like the leg, because they stay stable for a longer period of time. The bullet, when traveling sideways, makes bigger holes. 3. Fragmentation. The 5.56 and 6.8 and the west german 7.62 will fragment when they yaw if traveling fast enough. The US-manufactured 7.62 tends to not do this. Whether a bullet fragments or not depends on bullet construction and such variables as jacket thickness. Fragmentation make very big holes indeed, BUT the bullet has to have the right construction and be traveling fast enough. 4. ‘Controlled expansion’. The classic hollow point profile causes the bullet to expand. Not typically used in military rounds, but this can be operative over a greater range of bullet velocities than fragmentation. In addition there is a wildcard, the ‘temporary cavity’. The human body is mostly water and on bullet impact a shock wave can stretch the muscles and internal organs to create a temporary cavity that rapidly returns to the original size. Normally this causes no permanent damage, with a few exceptions, such as the liver. All bullets use mechanism 1, bullet diameter. Some bullets use mechanism 2, yaw. If the bullet is over-stabalized it may exit the body before yaw starts. Some bullets use mechansim 3. In particular, the 5.56 can if it travels fast enough and depending on variables like what factory the bullet came from in the recent 62 grain bullet production. But the M-4 carbine and the 14.5′ barrel barely gets it going fast enough for this to occur reliably, and then usually only within a range of 50-75 yards. The 10.5′ commando carbines didn’t achieve this past point-blank range. This is a problem, because all the cool kids want short weapons these days. You see this with the XM-8, where the standard issue weapon will apparently be a carbine with a 12.5′ barrel. This is, I think, a disaster waiting to happen for stopping power, since only mechanisms 1 and 2 will reliably work. If they want a short weapon they should change the round to 6.8 SPC, which will still fragment at the lower velocity. The temporary wound cavity is really the only mechanism possible for the ‘knockdown power’ proponents. the temporary cavity depends a lot on bullet velocity. The skeptics point out that the blended metal bullets are basically just light, fast bullets that make a big temporary cavity. Many terminal ballistics experts are highly skeptical of the temporary cavity mechanism. It seems that because it lacks a physical damage mechanism, it would have even more variable results on the people hit. It’s hard to argue with a big, gaping, bleeding hole. Given a choice I think you’d always want a permanent hole rather than a temporary one.

  11. Well I can’t fault the ‘big, gaping, bleeding hole’ line. That’s definetely what I’m after in a combat round. I agree also that the yaw and fragmentation are important, since the hague conventions won’t let us use most of the good hollowpoint rounds for faster expansion. I think we should start issuing 2 SMG style carbines per squad. Say a H&K UMP in .45 ACP. It’s a stopper. I was wondering what kind of performance we could get out of a .46 S&W type of round in a carbine. Big heavy bullet with a decent velocity. Should do well in a carbine with a 10′ barrel. Of course then you have specialization, and you know how the army feels about that. What I want to know is, does the army employ an ballistic scientists? You wouldn’t think so, as this should’ve been noted and changed years ago.

  12. While I enjoyed Mr Blofeld’s comments about knockdown power, they are demonstrably untrue. Consider a simple fistfight; very often the punchee falls down from a single good blow, yet the puncher doesn’t. People are not inherently stable like, say, bricks, and fall down for vastly different reasons. For instance, a Taserdart has negligle kinetic energy, but knocks people down through a different mechanism. Seems to me that the debate between 6.8 SPC and 6.5 Grendel depends mainly on the trade-off between long range accuracy and energy plus armor penetration on one hand, and fragment-induced short range damage on the other. I’d think that a much more important consideration would be performance in very short barrels, since the PTB seem intent on fielding a very expensive, glorified machine pistol as our next assault rifle. The best cartridge in a 20′ or even 16′ barrel is irrelevant when you’re actually using 14′ or even 10′ or 12′ barrels.

  13. Very true, that short-barreled weapons seem to be the wave of the future in chemically powered weapons. Both the 6.5 and 6.8 seem to be burning quite a bit of powder after the bullet leaves the barrel in the short weapons. This means that they’re not efficient in these weapons. Mind you, I did not say effective, I said efficient. Once again, I have to wonder if either is the right round for the job. The more I read, if my choice would be limited to these two rounds, I’d pick the grendel. (It’s got a cooler name ;)) I still think we need to go to the 8mm range, or even larger. Why not use the ‘scale’ of the grendel (low B.C.) and build a larger diameter round? Form and function are about the same, just more Ft. lbs.!

  14. Why are we so interested in making a shorter rifle? It’s nice to have a short weapon while clearing rooms, other than that, who cares? In my years as a Marine and now as a Soldier, I cannot ever recall anyone saying, ‘I wish my rifle was shorter.’ I’ve heard: ‘I wish this piece of shit would not jam’ and ‘I hope these assholes aren’t wearing body armor,’ and the classic ‘got any M-14’s left back there?’But never ‘I wish I had a shorter, less accurate and less lethal weapon.’Is anyone actually listening to what the troops want? If overall length is such as issue, let’s look at bullpup designs. The Steyr and FA MAS have full-length barrels with relatively short overall length. I know so people don’t like them because it is difficult to switch shoulders with one. I can’t recall ever firing from my left shoulder even in MOUT training. If I did, it would be such an exercise in ‘spray and pray’that rifle design would not matter much.

  15. Short rifles have been much requested lately because people are piling in and out of vehicles all day. The general trend in rifle designs is to reduce length; that was the reason for the bullpups like the AUG, Tavor, etc.

  16. The shorter rifle seems to be the wave of the future, and I for one am not real happy with the inherent lack of accuracy involved. Oh, don’t get me wrong, getting in and out of the HMMWV all day with a long gun sucks, but I am not sure about what we can do to strike a happy medium. I’d like to see less of a generic take on squad make-up, and see a variety of weapons issued. We need a heavier hitting long rifle, a few SMGs or carbines, a shotgun, and a really ripping LMG with a barrel cooling mechanism (CO2 or Freon, or some such), that has a true ‘quick change’ barrel. If they can all (except the shotgun) shoot the same round, and it’s actually better than the 5.56mm (which a bigger round is almost guaranteed to be) Then we should go get it. Bullpups would involve some issues, but so will any other rifle. Personally, I say get the Tavor, and rechamber it to 6.5mm Grendel. That can be the carbine.

  17. ‘and a really ripping LMG with a barrel cooling mechanism (CO2 or Freon, or some such)” WTF? Are you sh^tting me?? Where in the h@ll are you going to find freon or CO2 in Afghanistan??? I was sooo freaking happy just to get hot chow and such. Can you even imagine the Log problems with getting enough freon or CO2??? Geesh….

  18. Let’s cut to the chase! My grandson is a Special Forces trooper and has been back and forth between Afghanistan and Iraq a number of times. He dosen’t give a hoot about physics. He and his fellow troopers are carrying .45s and M1-As because of MUCH improved knock down ability VS 9mm and M-16/M-4. Those who are there and using theze weapons on a daily basis have made this decision not some theorist!

  19. …possibly I think the best ammo would be 6.67… a combo/comprimise of 6.5 & 6.8 (actually 6.65), a piece of hell & heaven (6 & 7), it would be truely funny if this was the case… I like the 6.5 better (better stats overall from what I have read, The 6.5 Grendel performs with the same or more knockdown power as the 6.8 SPC at less than 200meters and seriously outperforms the 6.8 SPC at longer ranges), The chances that top brass will change ammo are probably when hell (or parts of their anatomy) freeze over because, any change is going to be expensive, we have stockpiles and company investments in 2.23/5.56, and the public isn’t just going to help out and buy a hunting rifle that shoots 6.5 or 6.8 unless a.) they are a true military enthuasist or b.) the rifle and ammo (hint, hint, hint… underscore, for all you companies out there) is nice and cheap. If 9mm can be altered to 9mm+p then current military ammo can hopefully be improved w/o insanely expensive overhalls in our guns, or at least I would like to think. I do like 6.8 as it would be the least expensive overhall, but I would go with 6.5 (if your going to go, go all out, or don’t go at all). Maybe adding an armor piercing load to a single (or multishot) underbarrel smart 25mm grenade launcher for armored vehicles (XM8-M25/oicw?) if you truely want that capability (maybe even therombaric?), and hopefully it won’t weigh 18 friking pounds. I hope 5.57 ammo can be improved on, as this would be the cheapest alternative for the U.S. (unless the XM8 is going to come in 7.62, and that would happen only if HK can fix the current heat issues [the underbarrel handle melted under substained fire testing]). I did read of a possibility of a hole being placed straight thru the center of a 2.23 bullet in the manufacturing process, which would not violate any current accords/treaties(?) to my (limited) knowledge. Otherwise my vote is for the 6.5mm Grendel.

  20. For the record, the United States didn’t sign the Hague Accords. We are not bound to it by ink. I’m pretty sure in paperpusherland they might opt for the Grendel and think of fanciful ideas to replace 5.56 -and- 7.62 at the same time. Perhaps issuing the rounds to death row firing squads (though I think only Utah still uses firing squad) would be interesting for wound ballistics studies.

  21. Shooting a few people doesn’t appreciably increase the known information. The Germans pulled people out of the concentration camps and shot them as they were developing their short round for the Sturmgewehr-43. The complexity of the human body makes for meaningless statistics unless you have many many events. That is why Fackler et al. developed ballistic gelatin. The tough part was correlating the gel to the known characteristics of wounds. Fackler was a combat surgeon, and had literally thousands of bullet strikes in his data base. Back in the Spanish American War, Roosevelt wrote (The Spanish were using 7mm Mauser!) When a soldier is hit in the head, heart, or spine he dies quickly. When a soldier is hit anywhere else, he survives, and recovers amazingly quickly. Different tissues respond differently. The liver will tear, but has less high pressure blood flow, so the person shot may die, but may not be stopped. If you put your rounds between your enemy’s chin and breastbone, you will have good results, almost no matter what you use. If you carry an M-14, you will be carful how you use your few rounds, and wait that extra quarter second to get on the enemy’s centerline. I am developing a bullpup rifle that lets you have a 24 inch barrel in a 28 inch rifle. Further, convert from one ammunition to another by changing the barrel and magazine. Capable of firing 12 gauge, 7.62mmX51 or 5.56×45. Downward ejection for high reliability and ambidexterous operation.