The 6.8 SPC should have been the 6mm SPC


PDA






rizbunk77
March 1, 2009, 01:41 AM
The 6.8 SPC was a good try but not a good final result in terms of being usefull over extended ranges. Not a good all around performer. 115 gr. is too heavy and slow in that little case. In addition 115 gr. is too light in a .277 diameter bullet to have a high BC. I believe however that an 87-95 gr, .243 bullet would match up very well with this case and offer substantial terminal performance. This would also extend the usefull range of the cartridge several hundred yards due to incresed velocity and ballistic efficiency. I have used such bullets on large mulies with devastating results in close quarters, as well as at ranges approaching 200 yds. Far surpassing anything the 5.56 would be capable of.
I have read where early wildcat development of a 6mm SPC has yielded at least 2700 FPS with a 107 gr. Bullet. Decreasing the bullet weight some small amount (to 90 gr?) could increase velocity to near 3000 fps. This would be an extremely effective, efficient and small military round. Also very low recoil.
If they ever come through on caseless smart ammo though, this is all irrelevant.
Ruger should chamber their rifle for such a cartridge. Do it in the target configuration with Hogue stock and medium weight 20" barrel

If you enjoyed reading about "The 6.8 SPC should have been the 6mm SPC" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
Zak Smith
March 1, 2009, 01:47 AM
Perhaps for your use. Its actual inventors had something else in mind, and they did test what you suggest:

http://demigodllc.com/articles/6.8-mm-spc-cartridge-history-development-hornady-stag-arms-carbine/

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.

Numerous articles and Internet rumors have suggested that the SPC designation means 6.8 is good only for Close Quarters Battle (CQB), but not distant targets. This is incorrect, and contrary to the intent of the project and capabilities of the cartridge.

rizbunk77
March 1, 2009, 02:45 AM
Ballistics tables don't lie.
A basic narrative of the 6.8 cartridge is that you start with a slow muzzle velocity, then you compound that with a bullet that has a low ballistic coefficient. This is not a good combination for a service rifle. 6mm beats the 6.8 because the muzzle velocity is higher and it would retain energy much better. It would also penetrate better. My guess is that it was dismissed out of hand as being too small due to pre-existing predjudice.
Honestly, a 6mm 90 gr. bullet fired above 3000fps is devastating. This round would have all the terminal performance needed in just about any situation and would be superior or equal to the 6.8. Even the 6.5 (to split hairs) would have been a better choice than 6.8.
I agree with the late Jack O'Connor that the 270 is a hell of a caliber but not when you stuff the lightest 270 bullet you can get into a small rifle case.
http://www.remington.com/products/ammunition/ballistics/comparative_ballistics_results.aspx?data=R68R1*R68R2*RM68R1*PRC68R4

You can see here that the 6.8 produces roughly half the energy necessary to reliably kill deer at 500 yds. Yep, sounds great to me...
I simply don't buy that the most accurate rounds were from 6.5 to 7mm. The best rounds available for match shooting today are the 6mm's. 6BR 6PPC etc.

IndianaBoy
March 1, 2009, 02:53 AM
6.5 Grendel is the way to go.

DeathByCactus
March 1, 2009, 03:51 AM
This is not a good combination for a service rifle. 6mm beats the 6.8 because the muzzle velocity is higher and it would retain energy much better. It would also penetrate better. My guess is that it was dismissed out of hand as being too small due to pre-existing predjudice.

From article:
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.

Dunno man, what's done is done. With the crappy economy I don't see anyone changing to anything anytime soon. However, I don't shoot extended ranges, just your normal range of 1-250; 6.8 works fine for me. The FPS difference is like magazine masturbation, it all does the job.

Besides, I doubt law enforcement would be interested in the 6mm due to its better (from what you say, I dunno) penetration power. Off. 1, "Tango down!" Off 2, "So is the guy in the other building!"

Kind of Blued
March 1, 2009, 04:39 AM
I think it's a fine cartridge and posts good numbers, but I'm more convinced it should be named the "All-purpose cartridge" as opposed to the "Special-Purpose Cartridge" which is basically the exact opposite.

I can't think of one situation in which it's the perfect cartridge for the job, and I also can't think of one cartridge which I would rather have for all across-the-board combat purposes.

Also, it depends on who we're marketing toward. If it's the US Military, I'd be concerned about getting the bullet moving fast enough to cause the damage associated with velocity, but making the biggest hole I could at the same time, assuming that we're talking FMJ bullets. Judging by what Zak Smith posted above about finding the "sweet spot" between 6.5mm and 7mm bullets, I'd say that's exactly what happened with the 6.8 SPC.

Sunray
March 1, 2009, 05:43 AM
"...Special-Purpose Cartridge..." That being a marketing thing.
The 6.8 SPC was/is rumoured to be the next U.S. military cartridge with no request from the U.S. military. A 100 grain .243 is a better bullet, ballistically, faster and flatter, but since the U.S. military isn't going to be ramming yet another cartridge down NATO's throat any time soon it really doesn't matter.

CB900F
March 1, 2009, 08:13 AM
Fella's;

I agree with IndianaBoy. The 6.8 had some real teething problems & I'm not sure they won't arise again to bite that cartridge in the butt. In any case, it seems as though it's nothing more than an attempt to reinvent the wheel & avoid paying Alexander Arms their rightful royalties for the Grendel.

I don't have a 6.5 Grendel, but could see myself owning one, if possible, in the future. I don't see myself owning a 6.8.

900F

420Stainless
March 1, 2009, 10:01 AM
I like the ballistics just fine with the 6.8 SPC. I'm looking forward to cranking out some hunting loads for next year now that some brass has finally become available.

Tony50ae
March 1, 2009, 10:38 AM
I think what is being forgotten here is that the 6.8 was designed to drop the bad guys better than the 5.56 at greater distances. The 5.56 depended on its high velocity to deliver its punch. Then the Army and Marines stated using the M4 with its much shorter barrel. The 5.56 didn't put them down at extended ranges like it did in the longer barrel. The 6.8 with its larger bullet was supposed to help alleviate that problem. The 6.8 SPC delivers greater energy than the 5.56 mm NATO(M4 configuration) at 100-300 meters.

The round was a collaboration between memebers of SOCOM and Remington.

Dr. Tad Hussein Winslow
March 1, 2009, 03:18 PM
While I agree that something like the 6x45mm, which is a popular wildcat in its own right (or a 6mm based on the .30 Rem case), would be an EXCELLENT all-purpose cartridge in a light rifle for the military, and *significantly* better at all ranges than the 5.56, particularly longer ranges, from looking at what Zak posted about the origins of the 6.8 spc, it was determined that the 6.8 bullets were more devastating than 6mm bullets, even though going slower, and even though slowing down more quickly, due to relatively poor BCs. There's just something to be said for bullet size, in creating wound channel.

But both are far better, IMO, than 5.56 for a select fire rifle, if you don't take into account mag and ammo cost & availability. But reliability is even more important than terminal ballistics, which is why the 6.8 has edged out the 6.5 grendel for the most part. I'd like to SEE the common *debate* become "6.8 spc vs. 6.5 grendel vs. 6x45mm" instead of just "6.8 spc vs. 6.5 grendel", because there is such strong merit in a 6.0mm bullet going faster (extending PBR), with a better BC, albeit slightly lighter, in the 85-87 gr range.

As for us "non-wealthy, non-military", who cannot get full-autos due to the 86 ban and resulting prices, then NONE of the above make much sense. Makes more sense to step up to a higher powered round such as .243, .260 rem, 7mm-08, etc. This is why I now have a DPMS LR-260L - as light as most AR15s, more power than a 6.5 grendel, even out of a short barrel, and even with light/conservative loadings. There's just no reason to step *down* to a 6.8 spc or 6.5 grendel, if you're not trying to control the gun on target in FULL AUTO (unless you can't handle a 7.9 lb DPMS light rifle in a full powered cartridge, or unless you like a lot of doodads on the rifle, and so every conceivable weight savings is critical).

Now if the unconstitutional (IMO) 86 ban/moratorium were lifted, then I'd be singing a different tune. In that event, it'd be fun to get a 6.8 or 6.5g and see if it can be held such that at least 3 shots hit a man-sized target before being thrown off due to muzzle climb.

P.S. I would also note that a 6mm round would be *slightly more* controllable in full-auto than say, 6.8 SPC

P.P.S. Also don't rule out .257 bullets as the arguable sweet spot - they split the difference between 6mm and 6.5mm. What about a .257 SPC or 6.25x45mm? 100 gr quarter bore bullet, going quite a bit faster than the 6.8 SPC - THEN we'd be cooking with butane, no!? :p

gripper
March 1, 2009, 06:13 PM
On a related note, the Chinese 5.8mm ( especially in th eheavy sniping load) seems to bear out the benefits of a heavy for caliber 6mm,high BC,exterior and terminal ballistics etc.Seeing as the Canadians are allowed to inport a 5.56 mm semi auto variant of the QBZ95,I wonder if anyone has manan=ged to acquire some of th echicom ammo for analysis &duplication???

Zak Smith
March 1, 2009, 06:23 PM
The 6.8 SPC was/is rumoured to be the next U.S. military cartridge with no request from the U.S. military.
It was invented by personnel from the 5th SFG.


"...Special-Purpose Cartridge..." That being a marketing thing.
Again, pretty clear it followed the naming convention from the Mk12 SPR - special purpose rifle

The SPC designation was assigned based on the intended integration into the Mk12 Special Purpose Rifle (SPR).


In any case, it seems as though it's nothing more than an attempt to reinvent the wheel & avoid paying Alexander Arms their rightful royalties for the Grendel.
Might want to check the timelines and pedigree before making that assumption. Also note that they discarded the case-head size that 6.5 Grendel ended up with due to bolt reliability issues.


it was determined that the 6.8 bullets were more devastating than 6mm bullets, even though going slower, and even though slowing down more quickly, due to relatively poor BCs. There's just something to be said for bullet size, in creating wound channel.
Yes. If you look at the external ballistics of the 6.8 SPC, it's basically the same as 77gr 5.56, which is standard ammunition for the Mk12 SPR rifle which they were very familiar with. Since the primary goal of the SPC project was to produce a round with better terminal ballistics, and they ended up with something no worse than Mk262, I think we can conclude that for this purpose, they found the external ballistics of Mk262 to be acceptable. They could have achieved better long-range ballistics at the expense of terminal ballistics and they didn't.

Now we can all argue about what trade-offs we prefer, but that is the trade-off they made.

Howard Roark
March 1, 2009, 07:24 PM
Two guys at the USAMU did the actual testing and development of the final design. Zak is absolutely correct the 5th SFG originated the idea.

Murry tweeked the rifle to make it work and Troy Lawton developed and tested the loads to perform to specs.

I seriously doubt anyone here has more resources or talent than the above mentioned. Anyone that can do better might want to give LTC Frank Muggeoa call down at Bld 243 and apply for these guys jobs.

Acera
March 1, 2009, 10:04 PM
And if Remington pushes/markets it hard, those will get lost in the mix by the .30 Remington AR.

http://accurateshooter.wordpress.com/2008/10/15/remington-introduces-new-30-remington-ar-cartridge/




No matter if they have slightly better ballistics.

rizbunk77
March 1, 2009, 10:13 PM
Dr. Tad,

I am totally on board. Finally someone speaking my language.

Brazos
March 1, 2009, 10:56 PM
I am with Dr. Tad's closing P.S.S. I think a .257 version of the 6.8mm SPC would have made an awsome deer caliber. It would have to be close to the .257 Roberts. I have thought that since the 6.8 came out. I would like to build up a lght deer rifle based off the AR-15 platform and the 6.8 seems like the best choice at the moment but a .257 would have been excellent.

Brazos

Zak Smith
March 2, 2009, 12:16 AM
I forgot to mention that I have shot 6.8 SPC on full auto. I found it approximately as controllable as an M4 on FA.

gga357
March 7, 2009, 08:51 PM
I guess those who have invested the time and money in the round ddecide to market/introduce a round that they are willing to back with money or marketing or product.

If you enjoyed reading about "The 6.8 SPC should have been the 6mm SPC" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!