Originally Posted By hi-tech-rancher:
Thanks for posting again realteacher....haven't heard from you in a while.

The 12 twist 3 groove is the lowest pressure barrel I have ever fired.  In it, I can safely shoot 32 grains of H322 behind a 110 grain Sierra Pro Hunter (don't try this at home kids!).  When I load these, the powder compression sounds a bit like a car tire rolling over loose gravel .  Anyway, we measured this load at around 58,000 PSI in that barrel, which is equivalent to M193 5.56.

-the 110 SPH screams out of this barrel at 2860 FPS, and leaves a tennis ball sized hole in the far side of a deer.  This is not for the meek or mild, but I have never popped a primer, nor have I ever seen the brass flow in to the ejector hole with enough force to actually gouge the case rim.

-I cannot shoot this same load in my CA 11 twist 4 groove without deep swipes, and my 16" CA with a Tubbs kit treatment and a few thousand rounds on her, shows swipes that I am not comfortable with.

Originally Posted By vmpglenn:


I have a question about pressure values:

Doesn't the 6.8 have to operate at lower pressures than 5.56 because the bolt face is wider, meaning the area around the bolt face is thinner and therefore weaker?

I'm not a metallurgist or an engineer, but I thought this was one of the limiting factors on chamber pressures for 6.5G...

I know we can get around this using 9310 steel, better locking lug design, etc, but this would mean yet another spec change to use 6.8 in an AR.

Originally Posted By hi-tech-rancher:
Thanks for posting again realteacher....haven't heard from you in a while.

The 12 twist 3 groove is the lowest pressure barrel I have ever fired.  In it, I can safely shoot 32 grains of H322 behind a 110 grain Sierra Pro Hunter (don't try this at home kids!).  When I load these, the powder compression sounds a bit like a car tire rolling over loose gravel .  Anyway, we measured this load at around 58,000 PSI in that barrel, which is equivalent to M193 5.56.
-the 110 SPH screams out of this barrel at 2860 FPS, and leaves a tennis ball sized hole in the far side of a deer.  This is not for the meek or mild, but I have never popped a primer, nor have I ever seen the brass flow in to the ejector hole with enough force to actually gouge the case rim.

-I cannot shoot this same load in my CA 11 twist 4 groove without deep swipes, and my 16" CA with a Tubbs kit treatment and a few thousand rounds on her, shows swipes that I am not comfortable with.

Originally Posted By PolyTechKID:
where does one go for a 12 twist three groove?

PTK

Originally Posted By MCA:


ARPerformance

Originally Posted By hi-tech-rancher:


That is about to change very soon.  When SSA gets their new powder in, they will release a new plinkiing / training round which should cost around $14 per box.  The only reason we don't have it now, is because of the ridiculous hoarding of ammo, by so many people that don't even shoot it.  When they finally get it and load the ammo, look for millions of rounds to hit the market.  The last projection was that it would be middle or end of July.

Why do you think I posted this now?  The last thing I want to see is a bunch of weak, lame 6.8 Remington SPC ammo on the market, because there are still so many SAAMI chambers out there, when  instead we could be getting 6.8 X 43 mm loaded 100 grain accubonds at 3000 FPS from a 20" barrel, and the 85 grain TSX at 3150 from a 16" barrel.

It is coming.   Just be patient.  

Originally Posted By Shoot-Look-Shoot:
I'm helping my brother build a new AR from scratch. It will be a 6.8SPC from either Bison Armory, TItan Armory, or AR15 Performance.
When you can fling a 90 grain bullet at over 3000fps from a 12.5 inch barrel, who needs the 5.56 anymore?

Originally Posted By 320pf:


"90 grain bullet at over 3000fps"

I am just curious, where is the source for this

320pf

Originally Posted By hi-tech-rancher:
[1) because I think the 6.8 kicks the 5.56's ass so badly that I don't have much need for that caliber any more......especially not the compromised version where a bullet, much heavier than that for which the rifle was designed, is "needed" to increase its lethality.  

Originally Posted By QuadBomb:


HTR, I don't follow you on this.  If it fits down the bore, what's the harm in using a heavier bullet?  Not being flippant, just curious.  If you can get a heavier bullet downrange without making a heavier gun, that seems to me to be a solution.

Personally I don't have much faith in the 5.56 at all, not for use against people.  That's why I use a 6.8.  But I'm trying to understand what you mean.

Originally Posted By MudBug:


Yeah, this makes no sense to me either.

There is nothing at all wrong with shooting the 77 grn bullets in a 5.56 rifle. They (And the 75's and even 80s) have been shot in high power/DCM matches for a long time.

Going by your logic on this I could say "The AR15? I don't have much need for that rifle anymore.... Especially not one of the compromised versions where a Caliber much larger that the rifle is designed for is "needed" to increase lethality."

Originally Posted By hi-tech-rancher:
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:

http://s153.photobucket.com/albums/s233/dkred5854/ARP1.jpg

http://s153.photobucket.com/albums/s233/dkred5854/DSCF7003.jpg

http://s153.photobucket.com/albums/s233/dkred5854/ARP4.jpg


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:


http://s153.photobucket.com/albums/s233/dkred5854/DSCF1034.jpg


(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, and Remington 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.

__________________

Originally Posted By hi-tech-rancher:
Anyway, we measured this load at around 58,000 PSI in that barrel, which is equivalent to M193 5.56.

Originally Posted By JTJ:


How did you measure the pressure in the barrel?
What is a pressure trace test?


JT

Originally Posted By MCA:


ARPerformance

Originally Posted By arowneragain:


I didn't see component barrels on their site - maybe I missed them?


Where else can one get a SS (or CM chrome-lined) 12-twist 3-groove 6.8 SPec II barrel?

If I build another AR, it may well be another 6.8, and 1) I want to build it myself, and 2) I want the best barrel available - preferably in a 20" configuration.

Originally Posted By hi-tech-rancher:

Actually, I am not sure you will find one.  I have never gotten the Speer 90 grain TNT over 3000 FPS from a 12.5 inch barrel.  I don't believe anyone else has, either.

What I have done, is to get the Barnes 85 grain TSX to 2975 FPS from a 12" barrel.  Perhaps that 's to what he was referring.

Originally Posted By arowneragain:


I didn't see component barrels on their site - maybe I missed them?


Where else can one get a SS (or CM chrome-lined) 12-twist 3-groove 6.8 SPec II barrel?

If I build another AR, it may well be another 6.8, and 1) I want to build it myself, and 2) I want the best barrel available - preferably in a 20" configuration.

Originally Posted By MCA:


You probably need to call or email him about it - pretty sure that would be a custom match grade barrel - not an off the shelf item.

Originally Posted By hi-tech-rancher:




I think that you have both misunderstood me.  Follow with me on this:

What I am saying is that the .223 was originally designed for 55 grain bullets, right?  Yes, there were 40's and 50's and then someone decided that, in order to increase lethality of the cartridge, there needed to be heavier bullets loaded in it.  Why?  Because, by that time the military was married to the M16, and therefore that would be the cartridge going forward.  A new caliber just wasn't in the cards.

So, the questions was raised. "If we can't kill enemy combatants that efficiently with 55 grain bullets, or, if they are too light to get through barriers, what can we do to improve this little tiny varmint cartridge's effectiveness?   We're stuck with 5.56 X 45mm, so what can we do to beef it up?  After all, this thing started out as a woodchuck, coyote and prairie dog rifle."

The answer was "heavier projectiles!"  Ok, so what's the problem ?  

1) This cartridge as never intended to fire 69, 70, or 77 grain bullets, because then you needed a different twist rate in the barrels than that which were issued.  The bullets are longer and take up case capacity which reduces velocity.  (anyone thinking "compromise" yet? )

2)  that also meant re-fitting all those weapons with 1:7 twist barrels.  

3) When you put a 77 grain bullet into the inefficient 5.56 X 45 mm case, you lose a HUGE amount of velocity when you fire it from the barrels that are increasingly issued, to both Mil and for LE, i.e 14.5" and 16" barrels. .  Every one of you knows that .223 kills because of its velocity.  With no velocity, it is a .22.

4) MK262 is good on soft targets but sucks for barriers.  M855 was believed better for breaching barriers, but has been questioned for anti-personnel use, since they don't frag, and hardened, non-expanding penetrator rounds could be expected to produce  pencil wounds.  Ask the Rangers that were in Somalia.

What all this means, is that, in order to get what everyone thought was finally going to be decent performance from a varmint cartridge on 150 -200 pound animals and possibly walls or car doors, etc, this required very significant compromises.  This is no surprise.  That's simply physics, and it cannot be gotten around.

Why does the 6.8 alleviate these compromises?

1) the .277 caliber is DESIGNED for larger animals, mid-sized game, and defeats barriers in a manner far superior  to any 5.56 bullet.

2) you don't need a long barrel to get a very high % of the cartridge's potential velocity.  In fact, 85 grain TSX's leave a 16" barrel at over 3100 FPS.    This is within its original design properties. No compromise is necessary.    With this capability, who cares if you can shoot a 77 grain bullet from a 5.56 gun at 400 FPS less!??

10-60 grains more bullet, at up to 400 FPS faster?  Is there really any comparison whatsoever?  Remember, for all practical purposes, this is the same gun. The analogy would be that, if the 6.8 were  "weak" with say, 90 grain bullets, and we had to increase the bullet weight to 130 grains to get good performance in gel, game, barriers, etc, then it already would have died long ago.  Velocity would have been poor because the extra long bullets would reduce case capacity and the twist rates required would have killed any chance for the faster loads and lighter bullets to evolve as the optimum.


ETA"  Mudbug, you have it exactly backwards.  Now, with 6.8 SPC, We all have much more versatile uses for our AR-15's because in 6.8 SPC, you can use the same 7 lb, carbine, and throw heavier bullets up to 400 FPS faster than you could with 5.56 (that is the 85 grain TSX example) .  I would say that FINALLY a cartridge has been designed around this particular gun.  And this cartridge makes it what it probably should have been all along.

Originally Posted By hi-tech-rancher:
One other interesting note on the cartridge's versatility.

Last night, I loaded 65 subsonic 6.8 loads.

these are :

-SSA brass
-130 grain Nosler / Combined Technology Ballistic Silvertips
-COAL of 2.295"
-7.2 grains of Trail Boss
-No crimp this time.  Plenty of friction during seating and I usually crimp everything, but there is little need for recoil protection for the bullet.
-Wolf Primer

Last time I shot these, I got 1.25" group at 100 yards, but that was with an eotech and 3X magnifier.  this time, I will break out the Zeiss 3-12 X 56 and shoot them off the bench.  I have a feeling these things will put a pigs eye out  

Originally Posted By 320pf:
I think that it is a VERY big stretch to consider the 6.8SPC a useful sub-sonic load/caliber.  

First, since the we are talking sub-sonic loads, the velocity is held constant thus the bullet energy if portional to the bullet weight. So a 130g bullet just does not deliver the "goods" at sub-sonic velocities.  For example, a 130g Nosler at 1080fps will only generate about 340 ft-lbs of energy at the muzzle. This compared to the 300-221 Fireball that shoots a 240g SMK at  620 ft-lbs or the 338 Specter that shoots a 300g SMK AT 780 ft-lbs. To put this in perspective, a 22 LR hyper-velocity bullet has a muzzle energy of about 140-145 ft-lbs, whilst a 357 mag and a 45 ACP have  muzzle energies of about 550 ft-lbs  and 450 ft-lbs, respectively.

Secondly, because of the low B.C. of the 130g Nosler (B.C.=0.433) the bullet velocity will drop to under 1000fps with only 290ft-lbs of energy at about 140yrds. Now compare this to the 300-221 Fireball shooting a .30 cal 240g SMK with a B.C. of 0.685 and the 338 Specter shooting .338 cal 300g SMK of  0.75.  The 300-221 Fireball drops to under 1000fps (~530 ft-lbs) at about 220 yrds. and the 338 Specter drops to under 1000fps (~670 ft-lbs) at about 240 yrds. Again, compare this to the the muzzle energy of a 357 mag or 45 ACP, but the 300-221 Fireball or 338 Specter deliver this at +200 yrds.

Third, the terminal ballistics of the 130g bullet will be pretty anemic.  Sub-sonic rifle bullets rarely if ever expand or fragment. (People have tried several difference ways to get sub-sonic bullets to expand but the success has been rather limited. In the 300-221 Fireball and the 338 Specter, sub-sonic bullets do most of their damage by "tumbling" in the target.  This occurs because the bullets are "long" for caliber and the center of mass is toward the base of the bullet. So the longer the bullet and bigger the caliber the more tissue damage, hence the better the terminal ballistics.  

Lastly, I doubt that the loads you list will cycle an AR15. I have tried Trail Boss in several of my 300-221 FIreball AR's (with the gas port in the pistol position) and have found the powder to be too fast to cycle the action.  In fact, what makes the 300-221 FIreball and the 338 Specter "ideal" specialized sub-sonic rounds is the fact the the high B.C. bullets are seated beep into the case limiting the case volume such that ~8-10g of powders like 2400, AA#9, H110, and W296 fill the case.  This results in consistent ignition of the powder and pretty tight groups out to 200 yrds. I can get about 3-4 in. groups at 200 yrds. using a 3x multiplier on a EoTech.

So I think that your post on the "One other interesting note on the cartridge's versatility"
which seems to claim that the 6.8 SPC is a viable sub-sonic round is overzealous promotion of the versatility of the 6.8 SPC and misleading.

320pf

Originally Posted By Tim_W:

I believe he has already killed hogs with that 6.8 using the same bullets with other sub-loads, I have seen the 6.8 cycle with sub loads personally.
So in this case I believe you do know how your 300/221 works and does not cycle but, you do not seem to have any experience with the
6.8 or know how the 6.8 works.  HTR is giving everyone here first hand knowledge about a cartridge he does have experience with not telling you about the cartridge you have experience with.
HTR is a physican and knows exactly where the brain stem is located, he does not need expansion to do the deed.

Originally Posted By DanW:
It does not cycle the
AR.  But who cares?  The whole point is stealth.  It just works like a bolt gun, albeit a strange one.

I've seen HTR fire it, and it sounds like an air gun.  It is truly a sight (or sound) to behold.

Originally Posted By 320pf:
I think that it is a VERY big stretch to consider the 6.8SPC a useful sub-sonic load/caliber.

First, since the we are talking sub-sonic loads, the velocity is held constant thus the bullet energy if portional to the bullet weight. So a 130g bullet just does not deliver the "goods" at sub-sonic velocities. For example, a 130g Nosler at 1080fps will only generate about 340 ft-lbs of energy at the muzzle. This compared to the 300-221 Fireball that shoots a 240g SMK at 620 ft-lbs or the 338 Specter that shoots a 300g SMK AT 780 ft-lbs. To put this in perspective, a 22 LR hyper-velocity bullet has a muzzle energy of about 140-145 ft-lbs, whilst a 357 mag and a 45 ACP have muzzle energies of about 550 ft-lbs and 450 ft-lbs, respectively.

Secondly, because of the low B.C. of the 130g Nosler (B.C.=0.433) the bullet velocity will drop to under 1000fps with only 290ft-lbs of energy at about 140yrds. Now compare this to the 300-221 Fireball shooting a .30 cal 240g SMK with a B.C. of 0.685 and the 338 Specter shooting .338 cal 300g SMK of 0.75. The 300-221 Fireball drops to under 1000fps (~530 ft-lbs) at about 220 yrds. and the 338 Specter drops to under 1000fps (~670 ft-lbs) at about 240 yrds. Again, compare this to the the muzzle energy of a 357 mag or 45 ACP, but the 300-221 Fireball or 338 Specter deliver this at +200 yrds.

Third, the terminal ballistics of the 130g bullet will be pretty anemic. Sub-sonic rifle bullets rarely if ever expand or fragment. (People have tried several difference ways to get sub-sonic bullets to expand but the success has been rather limited. In the 300-221 Fireball and the 338 Specter, sub-sonic bullets do most of their damage by "tumbling" in the target. This occurs because the bullets are "long" for caliber and the center of mass is toward the base of the bullet. So the longer the bullet and bigger the caliber the more tissue damage, hence the better the terminal ballistics.

Lastly, I doubt that the loads you list will cycle an AR15. I have tried Trail Boss in several of my 300-221 FIreball AR's (with the gas port in the pistol position) and have found the powder to be too fast to cycle the action. In fact, what makes the 300-221 FIreball and the 338 Specter "ideal" specialized sub-sonic rounds is the fact the the high B.C. bullets are seated beep into the case limiting the case volume such that ~8-10g of powders like 2400, AA#9, H110, and W296 fill the case. This results in consistent ignition of the powder and pretty tight groups out to 200 yrds. I can get about 3-4 in. groups at 200 yrds. using a 3x multiplier on a EoTech.

So I think that your post on the "One other interesting note on the cartridge's versatility"
which seems to claim that the 6.8 SPC is a viable sub-sonic round is overzealous promotion of the versatility of the 6.8 SPC and misleading.

320pf

Originally Posted By 320pf:


First, you seem to ignore all of the terminal ballistics discussion and seem to be focused on the "silence" of shooting sub-sonic ammo through a can.  The second point is that at 200 yrds the sound of the action cycling is pretty hard to hear.

If you truly want "stealth" you would be better off with a Thompson-Center with a can.  A "break-open" can be made to work pretty quietly.  But the follow up shoot is pretty slow.  

You are just going to have to face it, as far a shooting sub-sonic loads the 6.8 SPC is pretty lousy compared to the 300-221 Fireball and the 338 Specter.

320pf

Originally Posted By 320pf:


First, you seem to ignore all of the terminal ballistics discussion and seem to be focused on the "silence" of shooting sub-sonic ammo through a can.  The second point is that at 200 yrds the sound of the action cycling is pretty hard to hear.

If you truly want "stealth" you would be better off with a Thompson-Center with a can.  A "break-open" can be made to work pretty quietly.  But the follow up shoot is pretty slow.  

You are just going to have to face it, as far a shooting sub-sonic loads the 6.8 SPC is pretty lousy compared to the 300-221 Fireball and the 338 Specter.

320pf

Originally Posted By 320pf:
TW, HTR, and DanW:

Please try and keep your post to a technical nature.  I have simply presented the ballistic data for 130g, 240g and 300g .277, .308, and .338 bullets, respectively.  The Bottom line is that the sub-sonic ballistics of the 130g .27 bullet SUCK.

HTR, In part,the terminal ballistics of sub-sonic rounds are similar to an arrow in that they do most the the dirty deed by crushing tissue and inducing hemorrhaging. A larger caliber-longer tumbling bullet has a better wound profile than a smaller-shorter bullet. PERIOD! Moreover, the heavier bullets WILL penetrate deeper that a lighter bullet.  So a heavier bullet wins. Unlike an arrow, tumbling sub-sonic bullets can and do regularly break large bones and this is done by bullet mass and energy.  So a heavier bullet wins again!  Given similar velocity (subsonic) one has to conclude that relative to the heavier bullets, light sub-sonic bullets are a poor choice.  

I am sure that you are very stealthy fumbling around changing mags and cycling the action to change from super sonic to sub sonic loads or it it the other way around??

DanW, I have literally shot thousands of sub-sonic loads and almost all of them through an AR. So I guess I am not as easily wowed by the lack of report as I once was. With the proper sub-sonic cartridge such as a 338 Specter or 300-221 Fireball a practiced shooter can hit a 10 inch plate 9 out of 10 times at 200+ yrds and if you are really dialed in 10 for 10 is doable without too much effort.

I do agree that this conversation is not very productive given the audience. So I will depart from the 6.8 playground and let you all enjoy yourselves.

Pass the Kool-Aid please,

320pf

http://www.geocities.com/donovn1/triviagm.jpg

Originally Posted By hogzilla:


I know that you said in a reasonable price range (and this is waay out of mine), but Trijicon makes an ACOG equiped with a 6.8 bullet drop compensator.

Hope that helps.

Originally Posted By fook:
Well, fuck me three times....



I want to be the first kid on the block with a 6.8. So I go on ARFCOM to find out what/who/where to buy.



By the time my upper is built, I hear about excessive pressures from incorrect twist rate and # of grooves in the barrel.



OK, no problem. Order another 'correct' barrel and rebuild the upper assembly.



Oh, fuck me, what? The shitload of SSA ammo is too hot and should not be used?  Wonderful.



NOW I come to find my 'correct' barrel is also junk due to the leade, or lack thereof.



Since 6:37 CDT this morning, I have been kicked by a fucking cow, find out I left my prescription pain killers from my wasted ACL in Houston, had a fat chick back into my truck, and now am told my 6.8 build is STILL an unsafe POS.


If I PM someone my address, would you be so kind to stop by and shoot me in the head with a .38 RNL?


thank you

Originally Posted By 320pf:
I think that it is a VERY big stretch to consider the 6.8SPC a useful sub-sonic load/caliber.  

First, since the we are talking sub-sonic loads, the velocity is held constant thus the bullet energy if portional to the bullet weight. So a 130g bullet just does not deliver the "goods" at sub-sonic velocities.  For example, a 130g Nosler at 1080fps will only generate about 340 ft-lbs of energy at the muzzle. This compared to the 300-221 Fireball that shoots a 240g SMK at  620 ft-lbs or the 338 Specter that shoots a 300g SMK AT 780 ft-lbs. To put this in perspective, a 22 LR hyper-velocity bullet has a muzzle energy of about 140-145 ft-lbs, whilst a 357 mag and a 45 ACP have  muzzle energies of about 550 ft-lbs  and 450 ft-lbs, respectively.

Secondly, because of the low B.C. of the 130g Nosler (B.C.=0.433) the bullet velocity will drop to under 1000fps with only 290ft-lbs of energy at about 140yrds. Now compare this to the 300-221 Fireball shooting a .30 cal 240g SMK with a B.C. of 0.685 and the 338 Specter shooting .338 cal 300g SMK of  0.75.  The 300-221 Fireball drops to under 1000fps (~530 ft-lbs) at about 220 yrds. and the 338 Specter drops to under 1000fps (~670 ft-lbs) at about 240 yrds. Again, compare this to the the muzzle energy of a 357 mag or 45 ACP, but the 300-221 Fireball or 338 Specter deliver this at +200 yrds.

Third, the terminal ballistics of the 130g bullet will be pretty anemic.  Sub-sonic rifle bullets rarely if ever expand or fragment. (People have tried several difference ways to get sub-sonic bullets to expand but the success has been rather limited. In the 300-221 Fireball and the 338 Specter, sub-sonic bullets do most of their damage by "tumbling" in the target.  This occurs because the bullets are "long" for caliber and the center of mass is toward the base of the bullet. So the longer the bullet and bigger the caliber the more tissue damage, hence the better the terminal ballistics.  

Lastly, I doubt that the loads you list will cycle an AR15. I have tried Trail Boss in several of my 300-221 FIreball AR's (with the gas port in the pistol position) and have found the powder to be too fast to cycle the action.  In fact, what makes the 300-221 FIreball and the 338 Specter "ideal" specialized sub-sonic rounds is the fact the the high B.C. bullets are seated beep into the case limiting the case volume such that ~8-10g of powders like 2400, AA#9, H110, and W296 fill the case.  This results in consistent ignition of the powder and pretty tight groups out to 200 yrds. I can get about 3-4 in. groups at 200 yrds. using a 3x multiplier on a EoTech.

So I think that your post on the "One other interesting note on the cartridge's versatility"
which seems to claim that the 6.8 SPC is a viable sub-sonic round is overzealous promotion of the versatility of the 6.8 SPC and misleading.

320pf

Originally Posted By Maryland_Shooter:

I bought a Cardinal, right when the bad batch went through the place.  Tested with SSA higher pressure loads and it looks OK.  My luck was good.

Originally Posted By Desert_AIP:


Same here.

I bought two and have shot combat loads and handloads through both with no pressure signs.
Good shooting barrels too!