The 6.8 SPC could have been a winner if...

... okay...

Not that I agree or disagree on any particular point, but... where are you going with this?

actually I disagree that it's not the CALIBER that could be changed to offer the biggest improvement but rather the case length

Lop off 4mm and you'd have opened the door to all kinds of excellent .277 projectiles in much more aerodynamic profiles

The problem with 6mm is it's just not that much different than 5.56 and to the extent of what the SPC was developed for size does matter with regards to the bore


As I see it though the SPC is a cartridge that sold it's soul to the velocity devil at the expense of bullet mass, SD and BC

From an armchair I suppose it's all a puzzler. The round was developed by guys who shoot people for a living and 6.8 was the best performer for what they wanted. I don't think 6mm was even considered as it didn't do anything much better than 5.56.

Optimizing a combat round for 6-700 meter shooting is silly.

Let's see, the SF and AMU worked to make a better, more lethal bullet downrange with the restriction it had to fit the M16 mag well no matter what, and mostly couldn't mess with the bolt face, as it had limits to what size it could accept.

For the military requirement, better range was good, but more foot pounds of force was also a goal, as that is a lot of what lethality is about. A bullet delivering more energy will be more lethal because it has more penetration and creates a bigger cavity which disrupts tissue and blood vessels. More damage means less fight from the recipient, which is the end goal. PAY ATTENTION: the military isn't necessarily looking for Dead Right There. Nice if you can get it, but remember, the worlds Armies already walked away from the .30, 8mm, etc. There is an effective limit to what works altogether in a package.

So, the 5.56 has to have more mass to carry more energy, as it's already on the upper limit in ballistic performance with speed. Making it faster will have quickly diminishing returns, like increasing barrel erosion. We already have to chrome it to keep barrel life up.

In general, bigger is better, but - BUT - only up to a point. You can quickly increase mass to deliver more energy. As the bullet gets more diameter, it also has to accomodate the ogive for streamlining, which makes the bullet seat out further. At that point something has to give - either the case becomes shorter, or the bullet can't get longer.

Add the mysterious art of cartridge case design, which so many of us seem to be uninformed about, and which is a common subject on wildcat forums. The length, diameter, shoulder, and case to neck ratio all have an impact not only on flame propagation, but also the mechanics of automatic feed, especially from magazines. In this specific situation, the M16 has a STRAIGHT magazine well and DOES NOT accommodate tapered cases very well. Highly tapered cases create a bigger problem in this lower trying to feed them, as the properly curved magazine to do it simply hasn't existed.

For those who quickly dismiss lethality as any valid reason in cartridge design, the real truth is that many combat cartridge designer test calibers and bullets on LIVE targets. Shooting pigs has been and continues to be a method to verify the assumptions and calculations that otherwise remain unproven. It would be more than derelict to design a cartridge and never actually shoot a live target until the first soldier is lined up in a GI's sight picture. Pigs are considered a comparable and valid test medium, and are used. When you shoot live targets and see a specific condition is met more often in one caliber combination - powder, case, bullet, and twist as a working team, you don't ignore it for another. The results have been achieved.

Given the existing restrictions - an overall length fixed regardless of whether it's optimum, a straight mag well that limits case taper, balancing bullet diameter and length, and a responsible upper limit on bullet speed, certain combinations get eliminated quickly. One such factor is that extensive military combat studies show the average soldier only shoots out to 400m regardless of the actual effective range of the gun they use. That was discovered when most battle rifles could shoot to 600-800m. Soldiers would not take the shots, and still won't, regardless of the complaints by long range enthusiasts.

With a 400m effective range "limit," it's a waste of effort to design for longer ranges, and compromises the design when used in shorter barrels - like the ISSUE 14.5" M4. No, the military does not have to comply with BATF rules in that regard - they even use 10" barreled weapons. The cartridge chosen would also need to meet the requirements of that use. The government doesn't need multiple rounds of the same caliber optimized for different length barrels, as the use of +P+ submachine gun ammo in the Beretta proved. If a soldier can get the wrong ammo, he will, even if it's not his fault. The cartridge is required to fit in the operating envelope, not the rifle to the cartridge. Those that complain about cheap low powered ammo not cycling their M4gery should take specific note.

Rather than complain about what a caliber is good for, it's probably a better perspective to understand how it got to be as good as it does considering all the dimensional and specific requirements it has to comply with. In that regard, the bigger than 6mm cartridges do a better job in the AR platform, and a lot of shooters already know that. The sales figures are right there, and they are winning.

They weren't looking to make a long range gun with great ballistics. They were looking for increased lethality out to 500 yards. The requirement was 500 ft-lb or more energy at 500 yards. They tested a 6mm but it didn't make the cut, perhaps due to the terminal ballistics?

Here's my frustration. A chance exists to pick any caliber, and .277 is chosen in this day and age? What genius was doing the brainstorming for that cartridge...

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Photo of SPC cartridge development:


More info at: http://www.m4carbine.net/showthread.php?t=19936&highlight=Grendel

6.8 mm SPC History and Development
Cartridge assessment began with the 6mm PPC case, necked up to 6.5mm. The 5th SFG soon discarded the fat PPC case due to poor magazine capacity and insufficient reliability in the M4. Their attention then turned to the .30 Remington case, which is essentially a rimless .30-30 Winchester. Its head and body diameters are larger than 5.56 (0.378 inch), but smaller than 7.62x39mm (0.445 inch). This thoroughly obsolete cartridge was chosen as the parent case because its smaller head diameter (0.422 inch) required less metal to be cut from the bolt head compared to the PPC or 7.62x39mm cases, which improves bolt service life. Several rebated-rim prototypes were created with an SPC body but 5.56's rim (0.378 inch) to utilize unmodified M4 bolts. After trials, it was clear the full-diameter rim helped extraction as compared to the rebated rim design.

Once the case dimensions were tweaked to fit and work in M4-compatible magazines, the project team quickly turned their attention to bore size. Derivative wildcats from 5.56mm to up 7.62mm diameter shooting bullets from 90 to 140 grains were subjected to a battery of tests, and a sweet spot emerged. The 6.5mm bullets showed the best accuracy and the 7mm bullets were the most destructive, but the 0.277-inch bullets showed almost the same accuracy and trajectory as the 6.5mm and almost the terminal performance of the 7mm. When necked down to 0.277-inch and shooting 115-grain bullets, it provided the best combination of combat accuracy, reliability and terminal performance for up to 500 meter engagements. This cartridge was deemed 6.8 Remington Special Purpose Cartridge (SPC), because 0.277 inch is 6.8mm in metric and .30 Remington provided the parent case.

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Matt304 said:

I personally would not be shooting live targets in combat.

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I totally agree

In fact I started a thread with this title awhile back. Totally agree that 6mm in that case would be a good improvement, while finding something that would get the 100 grain bullet going 3200 or so while being compact and logistically reasonable would be very lethal. I also like the 6mm OCC.
6mm's are much better than 22's (more so than most understand)

I agree with the 6mm fans... It seems if you could get it going fast enough, with match style 105 grain bullets it would have enough velocity to reach out and touch somebody out to 600m and still have plently of tumbling effect out to that distance. 6mm Hagar anybody? (Which i believe is based on the .30 rem case as is the 6.8?)

There is way too much disparagement about the 6.8 spc and I try to figure out why. I think maybe because it was touted as the 5.56 replacement. Many AR fans may of had other ideas of what should replace the 5.56, maybe AR fans didn't want any change at all. Maybe it wasn't AR fans shouting about it the most after all. Who knows, but I don't think I've read so many derogatory remarks about a particular rifle caliber ever.
Pistol calibers?....sure, there are diehards in almost every pistol caliber camp, but rifle calibers...? Not so much, at least not until the 6.8 spc was introduced.
All I mostly hear is that it sucks and the 6.5 Grendel is better. It's all rather immature.
I went 6.8 because I became interested in piston AR design rifles in a more effective caliber than 5.56. After reading about the research and development of the 6.8 and of many successful hunters using it, I was sold. Albeit I didn't go the piston route as they were more expensive, I took a leap of faith and went with a RRA DI rifle.
The AR platform was readily and apparently moderately easy to modify to accept it, the recoil is sublime, it is accurate and apparently quite effective within its limitations.
If some people don't like it.......well, I'm fine with that.

As Barnes and others make purpose built bullets for the 6.8, dimensions and the ogive are being tweaked to improve ballistic coefficient, which keeps creeping up as new bullets are released.

6.8 is becoming it's own bullet, not just another .277. And as loads are tweaked, users are reporting getting as much as 2970 fps from a 12" barrel, chronographed. Apparently you can push an 85 grain bullet with a military load and keep velocity nearly the same as the 5.56, from an 8" shorter barrel.

I like to believe that most of the people that own a 6.8SPC right now are shooters closer to resembling me than resembling a soldier. They've all got the wrong caliber

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Now thats what I'm talking about! I would think a 6mm that fits in an AR would be an ideal deer round because you can use an expanding bullet. I suppose if you are stuck with a OTM or FMJ, then 6.8 makes a little more sense... To me, its still just an improved 7.62x39


HB

The 30/06 was designed as a military cartridge too. I'd better not take mine hunting anymore.

It would have been a winner if it was marketed correctly. If it was called a short range deer/hog buster and repackaged as the 270 Bantam, it might become a winner, the new 30-30. Its a constant reinvention of the wheel, I know.

One thing that I can definately say for the 6.8 is that it does appear to reach its maximum velocity in a very short amount of barrel. For those going inside of buildings to clear out an enemy that is a great thing. That is what it was designed for. However, the war in Afganistan has proven to be a different kind of war. Everything you see or read about Afganistan is that our soldiers are being out gunned with longer range cartridges. It appears as though there is a need for something that can reach out there.

Optimizing a combat round for 6-700 meter shooting is silly.

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Tell that to the guys in the mountains of Afganistan. My point here is not to say that the 6.8 is crap, but that there is indeed a need for a cartridge that can reach out there when needed. Every war is different and should not be held to the same standard as a cartridge that was designed to fight in dense jungles of Vietnam where you most likely couldn't see 50 yards in front of you let alone 400-600 yards. It is ridiculous to me that the military can see a need for a new truck (MRAP) in Iraq, but it doesn't see a need for longer range weapons in Afganistan. Imagine how many troops could be supplied with an m14 or (heaven forbid) a 6.5 Grendel for the cost of one MRAP. In Iraq 10,000 MRAPs were ordered at a cost of about $500,000 each. So, we are okay with our troops getting out gunned in an actual battle as long as they can ride to the battle in style.

The 6.8 is great indoors. Go outside and the OP has got a point.

I still would be chambering the wildcat, 6mm version for a paper-puncher.

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6x47 is a very handy cartridge. Cheap too.

Longdayjake, I'm not HorseSoldier, but I think I follow his logic. Historically, grunts fight at sub 300m. The Germans noted this even during the Russian campaigns. The skill needed to hit 500m and furthur is pretty training intensive and the equipment (DM rifles) is what should be optimized for the longer ranges.

In a perfect world, every 11B or 0311 should be effective to a klick with his individual rifle, but that ain't going to happen. As it is, every good commander wants his guys to be deadly out to the infantryman's half kilometer.

I'm not HorseSoldier, but I think I follow his logic. Historically, grunts fight at sub 300m. The Germans noted this even during the Russian campaigns. The skill needed to hit 500m and furthur is pretty training intensive and the equipment (DM rifles) is what should be optimized for the longer ranges.

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I will not argue that most battles occur within 300 meters. What my point was supposed to convey was that our troops are being killed by under trained religious fanatics because we don't have the tools to shoot back. We are arguably the richest country in the world and we can't foot the bill for more .308 shooting marksmen? If they can shoot and kill us at long distance then we sure as hell should be shooting back. My point is that we can afford the training and the weapons, but for some reason we still depend on an underpowered cartridge. Why keep with the .223 when something else exists that can do both close and long range from the same platform?

Hows that for arm chair commando?