AR Performance
17 July 2009, 12:58
This was posted by HTR over on another forum, just thought I'd repost it here to see what you guys think. He ask us to spread it around.
"This might be a good time to do a "review of the state of the 6.8." What is my purpose? Well, there have been many changes since the first 6.8 Performance test I helped host at Wild River Ranch. I think it would be wise to help update those who have bought 6.8's and those still trying to sort out all the nuances of the newer specs like chamber, leade, and twist rates. At this point, I cannot state clearly enough that history is repeating itself.
Does everyone remember the .223 Remington, and how it later became the 5.56mm NATO? That is almost exactly what is happening with the 6.8 Remington SPC, which I now consider to be defunct. ( I define this as the market not wanting this any more, since there is a much better alternative available) What do I mean by this? I say "almost" because the 5.56 mm NATO was born out of a desire to increase velocity and the pressures necessary to produce them, when the US military adopted the .223 Remington, and then transformed it for military use. Given the longer leade of the 5.56 NATO chamber, the 5.56 mm cartridge could generate higher pressure and velocity. However, when firing this same cartridge in the slightly more snug .223 Rem chamber, pressure spikes could occur which would lead to parts failure or worse.
This is why it is generally not recommended that you fire 5.56mm NATO cartridges in .223 Remington Chambers.
And now, short of the US military adopting the 6.8 mm Rem SPC, history is repeating itself... Sort of... 2009 is very different from the 1950's and 1960's. The primary difference is that there is a huge and still-growing civilian market for AR-15 rifles, despite the near-50 year old design. Hey, the B-52 is still one of our workhorses isn't it? But, I digress....there is an ever growing demand for the rifle to produce more power, in terms of both combat effectiveness and for killing game, since so many hunters have begun using this rifle, as well. The big problem is that we have a magazine well, and mag that holds 2.30" of cartridge and that's all you get. Remember the Kohler commercial , where the lady asks the architect to "design a house around this..." and she shows him the kitchen faucet? There you have it!
In comes the 6.8 X 43 mm SPC. For now, this is what we will call the "new" cartridge. Its new chambers are currently known as "6.8 SPC II" (analogous to the 5.56 NATO) and the "6.8 DMR." (analogous to the .223 Wylde match chamber). You all know now that the original design (by Murray and Holland) was not what Remington released to the public, and it never met their claims of firing a 115 grain bullet at 2800 FPS from a 24" barrel. In fact, that misrepresentation almost, in itself, killed the whole idea. Shooters were rightly disappointed when what we got was really 110 grain bullets going around 2550 FPS.....YAWN. You should know that rifles chambered with SAAMI chamber and 1 in 10" twist could not consistently produce such a velocity with this bullet. The pressures are too high.
Then an amazing thing happened. Enterprising individuals like the proprietors of Ko-Tonics, Silver State Armory, AR Performance, Titan Armory, and others went "back to the drawing board," to create the genesis of what we have today. I like to call it the 6.8 X 43mm SPC. I hope someday we'll call it the "6.8 X 43 mm SPC NATO," but that is another story for another day. I don't think any of you can dispute that it is a clear evolution of the design, and superior to the Remington effort.
In fact, today's 6.8 X 43 mm SPC is NOT the 6.8 Remington SPC. There, I said it. Dimensionally the case is exactly the same. ONLY the chamber is different, because the first one to shoot the cartridge could not do so safely, when Remington tried to reach its velocity claim. The only "difference" one can argue is present in the "new" 6.8 X43mm SPC, is that the longer leade allows the COAL to be safely extended to 2.30". Remember that number from above?? Now, we can extend the OAL to full mag length, wringing out all the powder capacity this case can offer. The extra leade allows more powder capacity , thus more velocity at less pressure, and if we are lucky and the barrel designers are also smart enough to use thin lands, and 3, 4 or 5R, perhaps poly grooves, the pressure is even further ameliorated, and we now see velocities like the Barnes 85 grain TSX going 3100 FPS from a 16" barrel! Even better yet, the DMR chamber, designed by AR Performance, gives us Match accuracy in the 6.8. Just see my targets below and see what I mean. You can have this, too:
THE FIRST TWO USED A COAL OF 2.30" ( not the SSA factory, which I believe is loaded to 2.26." It must accommodate the SAAMI chamber )
As we have now shown you many times, some pretty astounding velocities are possible, with this cartridge, IF the barrel specs, chamber, rifling dimensions, and twist all come together for the ultimate low-pressure environment. It is very easy for a manufacturer to select 3, 4 or 5r rifling rather than 6 groove, 1 in 10" twist with larger lands:
(Source: 6.8 Performance test and pressure trace test, executed at Wild River Ranch, February, 2008. This was a GS custom 80 grain all-copper, Moly coated, banded bullet, fired from a max test load. Average vel. for this string was lower....3360 FPS)
Now, we can take full advantage of the parent .30 Rem case's exceptionally high efficiency, and with the .277 bullets we now have on the market, we have a completely new level of performance, with higher powder charge safely driving a longer bullet with a better BC. Can there be any argument that this is a major improvement?
So, for all of you that still believe it is a "wildcat," PLEASE do some homework. The following list will now include all the manufacturers that agree with us, that the 6.8 X 43 mm SPC is not only NOT a wildcat, but that a SPC II or DMR chambered rifle is is the SAFER of the two rifles, versus the SAAMI - approved design. If you reference the 6.8 performance test and report we posted in March of 2009, you will see that SAAMI chambers produced anywhere from 2 - 8,000 PSI more pressure for a given cartridge fired in two different barrels, when compared against one that had SPCII or DMR.
The old specs were in error, and it is now clearly established that, just as with .223 and 5.56, the longer leade chamber (and Match DMR ) are the ones appropriate for the "military pressure" 6.8 SPC cartridge. We do not know what to call the SAAMI approved- 6.8 REMINGTON SPC chamber, because it is essentially dead, as it was too short to allow for anything other than the REMINGTON load, which too, for all practical purposes, died a few years ago. We absolutely cannot explain why SAAMI continues to back the chamber which is exactly analogous to firing a 5.56 round in a .223 chamber for the 6.8 SPC. This is not something that ANY of you, as AR shooters, should have any difficulty understanding.
We also believe that SAAMI should recognize the SPC II and DMR chambers, since almost all manufacturers are now making 6.8 rifles with those chambers anyway. We believe that SAAMI should issue a recommendation to manufacturers to recall all SAAMI chambered rifles so that they may very simply be reamed to the .100 freebore dimensions of the SPC II chamber. Owners may opt to personally ream their own chambers or have local 'smiths do it. We believe that getting these barrels out of circulation will allow the final evolution of the cartridge to take place.....once and for all.
These Manufacturers now offer the proper, updated specs for 6.8 SPC. Their leade / chamber can shoot the new 6.8 X 43mm SPC which is analogous to the 5.56 NATO cartridge. Many of them have opted for slower twist rates, like 1 in 11" or 1 in 12" which we endorse, though we still see some 1 in 10" twist rifles that can handle very high velocity 6.8 X 43mm loads. Choose your twist based upon bullet length, density and weight.
AR Performance
Armalite
Barrett
Bison Armory
Bushmaster (Edit June 25, 2009.... I just received word that they have decided to go with 1:11 twist, 4 grooves and SPCII chamber....Bravo! )
Charles Daly Defense ?
CMMG
DPMS (as of 6/30/09, I confirmed that all chambers going forward will be SPC II, bravo DPMS ! )
JTAC Supply (offers Shilen and WOA barrels)
LWRC
LOTHAR WALTHER (Making all three chambers.....However, still providing the SAAMI chamber to some OEM's and I for one, wish they would recommend against it, or stop offering it altogether, as this perpetuates our problem.)
Noveske
MSTN (my understanding is that they use premium Douglas blanks and the SPC II chamber, but I need confirmation from them)
Patriot Ordnance Factory
Robinson Arms
Rock River Arms
Stag
Titan Armory
White Oak Armament
Those companies below, unfortunately, inexplicably, still do not make a 6.8 SPC II or DMR chamber. This makes their rifles potentially unsafe to fire the 6.8 X 43 mm SPC (like the 5.56) since it has something like a .223 chamber. Some even have selected twist rates as fast as 1 in 9.5 " which is suitable for .270 Winchester bullets of weights in the 130-160 grain range, and are generally not loaded in any 6.8 SPC ! We suggest that, given reasons of clarity and general safety, that you buy from the first group. If you reload or buy any factory ammo, you would not have to worry about whether your gun can shoot "military, combat, or tactical" pressure loads. You can buy anything currently loaded without having to think twice about that. If you buy one of these barrels, you will have to constantly work to find downloaded, lower velocity ammo that is on a par with the now-defunct Remington designed 6.8 SPC loads from 2003 - 2006.
Lewis Machine & Tool
Model 1 Sales
Ruger (Mini )
Remington ( only makes a bolt gun)
Note: in no way do I want to imply that the second list of manufacturers produces sub-standard quality guns or barrels. In fact, I own LMT, Ruger, Remington and Bushmaster products and I find them to be high quality. I just don't own anything in 6.8 made by them, and I won't until they make the updated spec barrels. The fact that they are still making SAAMI chambered guns makes it difficult for ammo manufacturers to produce 6.8 X 43 mm SPC ammo which can achieve the cartridge's full potential. That is the reason why we recommend that you buy from those using the updated specs. When all of the guns produced will fire 6.8 X 43 mm SPC, ammo MFR's will be free of the liability that might also come from, say, producing hot 5.56 ammo, in a market full of .223 chambered guns. It is just that simple. "
"This might be a good time to do a "review of the state of the 6.8." What is my purpose? Well, there have been many changes since the first 6.8 Performance test I helped host at Wild River Ranch. I think it would be wise to help update those who have bought 6.8's and those still trying to sort out all the nuances of the newer specs like chamber, leade, and twist rates. At this point, I cannot state clearly enough that history is repeating itself.
Does everyone remember the .223 Remington, and how it later became the 5.56mm NATO? That is almost exactly what is happening with the 6.8 Remington SPC, which I now consider to be defunct. ( I define this as the market not wanting this any more, since there is a much better alternative available) What do I mean by this? I say "almost" because the 5.56 mm NATO was born out of a desire to increase velocity and the pressures necessary to produce them, when the US military adopted the .223 Remington, and then transformed it for military use. Given the longer leade of the 5.56 NATO chamber, the 5.56 mm cartridge could generate higher pressure and velocity. However, when firing this same cartridge in the slightly more snug .223 Rem chamber, pressure spikes could occur which would lead to parts failure or worse.
This is why it is generally not recommended that you fire 5.56mm NATO cartridges in .223 Remington Chambers.
And now, short of the US military adopting the 6.8 mm Rem SPC, history is repeating itself... Sort of... 2009 is very different from the 1950's and 1960's. The primary difference is that there is a huge and still-growing civilian market for AR-15 rifles, despite the near-50 year old design. Hey, the B-52 is still one of our workhorses isn't it? But, I digress....there is an ever growing demand for the rifle to produce more power, in terms of both combat effectiveness and for killing game, since so many hunters have begun using this rifle, as well. The big problem is that we have a magazine well, and mag that holds 2.30" of cartridge and that's all you get. Remember the Kohler commercial , where the lady asks the architect to "design a house around this..." and she shows him the kitchen faucet? There you have it!
In comes the 6.8 X 43 mm SPC. For now, this is what we will call the "new" cartridge. Its new chambers are currently known as "6.8 SPC II" (analogous to the 5.56 NATO) and the "6.8 DMR." (analogous to the .223 Wylde match chamber). You all know now that the original design (by Murray and Holland) was not what Remington released to the public, and it never met their claims of firing a 115 grain bullet at 2800 FPS from a 24" barrel. In fact, that misrepresentation almost, in itself, killed the whole idea. Shooters were rightly disappointed when what we got was really 110 grain bullets going around 2550 FPS.....YAWN. You should know that rifles chambered with SAAMI chamber and 1 in 10" twist could not consistently produce such a velocity with this bullet. The pressures are too high.
Then an amazing thing happened. Enterprising individuals like the proprietors of Ko-Tonics, Silver State Armory, AR Performance, Titan Armory, and others went "back to the drawing board," to create the genesis of what we have today. I like to call it the 6.8 X 43mm SPC. I hope someday we'll call it the "6.8 X 43 mm SPC NATO," but that is another story for another day. I don't think any of you can dispute that it is a clear evolution of the design, and superior to the Remington effort.
In fact, today's 6.8 X 43 mm SPC is NOT the 6.8 Remington SPC. There, I said it. Dimensionally the case is exactly the same. ONLY the chamber is different, because the first one to shoot the cartridge could not do so safely, when Remington tried to reach its velocity claim. The only "difference" one can argue is present in the "new" 6.8 X43mm SPC, is that the longer leade allows the COAL to be safely extended to 2.30". Remember that number from above?? Now, we can extend the OAL to full mag length, wringing out all the powder capacity this case can offer. The extra leade allows more powder capacity , thus more velocity at less pressure, and if we are lucky and the barrel designers are also smart enough to use thin lands, and 3, 4 or 5R, perhaps poly grooves, the pressure is even further ameliorated, and we now see velocities like the Barnes 85 grain TSX going 3100 FPS from a 16" barrel! Even better yet, the DMR chamber, designed by AR Performance, gives us Match accuracy in the 6.8. Just see my targets below and see what I mean. You can have this, too:
THE FIRST TWO USED A COAL OF 2.30" ( not the SSA factory, which I believe is loaded to 2.26." It must accommodate the SAAMI chamber )
As we have now shown you many times, some pretty astounding velocities are possible, with this cartridge, IF the barrel specs, chamber, rifling dimensions, and twist all come together for the ultimate low-pressure environment. It is very easy for a manufacturer to select 3, 4 or 5r rifling rather than 6 groove, 1 in 10" twist with larger lands:
(Source: 6.8 Performance test and pressure trace test, executed at Wild River Ranch, February, 2008. This was a GS custom 80 grain all-copper, Moly coated, banded bullet, fired from a max test load. Average vel. for this string was lower....3360 FPS)
Now, we can take full advantage of the parent .30 Rem case's exceptionally high efficiency, and with the .277 bullets we now have on the market, we have a completely new level of performance, with higher powder charge safely driving a longer bullet with a better BC. Can there be any argument that this is a major improvement?
So, for all of you that still believe it is a "wildcat," PLEASE do some homework. The following list will now include all the manufacturers that agree with us, that the 6.8 X 43 mm SPC is not only NOT a wildcat, but that a SPC II or DMR chambered rifle is is the SAFER of the two rifles, versus the SAAMI - approved design. If you reference the 6.8 performance test and report we posted in March of 2009, you will see that SAAMI chambers produced anywhere from 2 - 8,000 PSI more pressure for a given cartridge fired in two different barrels, when compared against one that had SPCII or DMR.
The old specs were in error, and it is now clearly established that, just as with .223 and 5.56, the longer leade chamber (and Match DMR ) are the ones appropriate for the "military pressure" 6.8 SPC cartridge. We do not know what to call the SAAMI approved- 6.8 REMINGTON SPC chamber, because it is essentially dead, as it was too short to allow for anything other than the REMINGTON load, which too, for all practical purposes, died a few years ago. We absolutely cannot explain why SAAMI continues to back the chamber which is exactly analogous to firing a 5.56 round in a .223 chamber for the 6.8 SPC. This is not something that ANY of you, as AR shooters, should have any difficulty understanding.
We also believe that SAAMI should recognize the SPC II and DMR chambers, since almost all manufacturers are now making 6.8 rifles with those chambers anyway. We believe that SAAMI should issue a recommendation to manufacturers to recall all SAAMI chambered rifles so that they may very simply be reamed to the .100 freebore dimensions of the SPC II chamber. Owners may opt to personally ream their own chambers or have local 'smiths do it. We believe that getting these barrels out of circulation will allow the final evolution of the cartridge to take place.....once and for all.
These Manufacturers now offer the proper, updated specs for 6.8 SPC. Their leade / chamber can shoot the new 6.8 X 43mm SPC which is analogous to the 5.56 NATO cartridge. Many of them have opted for slower twist rates, like 1 in 11" or 1 in 12" which we endorse, though we still see some 1 in 10" twist rifles that can handle very high velocity 6.8 X 43mm loads. Choose your twist based upon bullet length, density and weight.
AR Performance
Armalite
Barrett
Bison Armory
Bushmaster (Edit June 25, 2009.... I just received word that they have decided to go with 1:11 twist, 4 grooves and SPCII chamber....Bravo! )
Charles Daly Defense ?
CMMG
DPMS (as of 6/30/09, I confirmed that all chambers going forward will be SPC II, bravo DPMS ! )
JTAC Supply (offers Shilen and WOA barrels)
LWRC
LOTHAR WALTHER (Making all three chambers.....However, still providing the SAAMI chamber to some OEM's and I for one, wish they would recommend against it, or stop offering it altogether, as this perpetuates our problem.)
Noveske
MSTN (my understanding is that they use premium Douglas blanks and the SPC II chamber, but I need confirmation from them)
Patriot Ordnance Factory
Robinson Arms
Rock River Arms
Stag
Titan Armory
White Oak Armament
Those companies below, unfortunately, inexplicably, still do not make a 6.8 SPC II or DMR chamber. This makes their rifles potentially unsafe to fire the 6.8 X 43 mm SPC (like the 5.56) since it has something like a .223 chamber. Some even have selected twist rates as fast as 1 in 9.5 " which is suitable for .270 Winchester bullets of weights in the 130-160 grain range, and are generally not loaded in any 6.8 SPC ! We suggest that, given reasons of clarity and general safety, that you buy from the first group. If you reload or buy any factory ammo, you would not have to worry about whether your gun can shoot "military, combat, or tactical" pressure loads. You can buy anything currently loaded without having to think twice about that. If you buy one of these barrels, you will have to constantly work to find downloaded, lower velocity ammo that is on a par with the now-defunct Remington designed 6.8 SPC loads from 2003 - 2006.
Lewis Machine & Tool
Model 1 Sales
Ruger (Mini )
Remington ( only makes a bolt gun)
Note: in no way do I want to imply that the second list of manufacturers produces sub-standard quality guns or barrels. In fact, I own LMT, Ruger, Remington and Bushmaster products and I find them to be high quality. I just don't own anything in 6.8 made by them, and I won't until they make the updated spec barrels. The fact that they are still making SAAMI chambered guns makes it difficult for ammo manufacturers to produce 6.8 X 43 mm SPC ammo which can achieve the cartridge's full potential. That is the reason why we recommend that you buy from those using the updated specs. When all of the guns produced will fire 6.8 X 43 mm SPC, ammo MFR's will be free of the liability that might also come from, say, producing hot 5.56 ammo, in a market full of .223 chambered guns. It is just that simple. "