Three years ago, I wouldn't have believed a 300 WSM could accurately deliver 125g Noslers at 4000 fps.





Nine months ago, I wouldn't have believed a 6.8 SPC could do what it is doing now.
<Inflammatory comments removed - Z>


 

well seeing that at 63,000psi or only 2000psi from max Hodgon puts 300WSM pushing a 125grn nosler at 3540 FPS tops. Yet you claim to best that by 500fps, please try to tell me that you're not vastly overpressure on an already high pressure chambering. I would love to hear the explanation on this one.

I ran the infamous 3200fps 6.8spc load past some very experienced members of a dedicated handloading forum, consensus is that pressures would be approaching 80,000 PSI.

Instead of getting busy attacking the few voices if velocity sanity on this site perhaps you should question as to why your loads are 500 fps + faster than any published data. Just because those velocities can be reached and not blow the firearm to pieces the first time does not mean that they're safe in any way. I doubt even the legendary ClarkKaboom would stand behind that 3200fps 6.8 load.




I don't doubt for a second you 6.8 guys would try to make up a 3200fps 110grn load, I don't want to see the velocity verified. I want to see the chamber pressure verified

Frankly, I've never heard of a 3200fps 110gr load in 6.8, either. I suspect the original poster of this info may be confusing 110gr loadings with the 85gr (Barnes TTSX) combat loads that Silver State Armory has verified out of a 16" 1:10 twist SPCII-chambered barrel at 3000fps, and could reach 3200fps out of a DMR-chambered 1:12 twist 18" barrel. Personally, I am with you; I would not want to be within twenty yards of a 3200fps 110gr load in an 18" 6.8SPC barrel.

I'm a big proponent of giving 6.8SPC a fair shake and I love handloading and shooting the round, but given the current state of the art, a 3200fps 110gr load is bordering on insane.

So how much of what powder was that again? <Inflammatory comments removed - Z>

I ran the "typical" load Tim_W posted on the previous page through QuickLoad.

110 gr Hornady OTM
32 grs Hodgdon 335

I set the OAL at 2.260" and barrel at 18"

83,796 psi.
2911 fps.

Okay then.

As this was one of those inane threads, I thought I would stay out... but you keep DRAGGING ME BACK IN!  (famous Pacino movie line quote, harhar).

GUYS, HEAD'S UP.  I WILL SAY THIS ONCE AND FOR ALL, SO THAT OUR REAL NUMBERS ARE NOT INVALIDATED, AND OUR CREDIBILITY REGARDING NEWLY DEVELOPED LOADS IS NOT DAMAGED: THERE IS NO 110 GRAIN 3200 FPS LOAD IN THE 6.8 SPC!!!

The highest velocity we obtained with the Sierra 110 Pro Hunter, from Constructor's 20", 12 twist, 3 groove, DMR barrel was 2960.

The load that is being confused is/are the 85 grain Barnes TSX and the GS Custom 80 grain bullet which we fired at 3150 in my CA 16" 11 twist, 4 groove, SPC II barrel and 3412 FPS in a 12 twist, 3 groove, DMR chambered 20" barrel.  We checked the velocity of the 80 grain GS with a different chrono and arrived at a mean of 3360.

When we fired the TSX, 85 grainer at 3150 from my 16" barrel,  that was only one round (through the same chrono we'd used for the entire test)  at 10 feet, and we were given this as a prototype only, therefore we did not report on it.  The load was not manufactured by anyone at that point, but now that SSA makes it, you can all buy, and shoot the same round from your 16" barrels at around 3000 FPS...right now.

Some of you seem very confused.  We have never claimed that the twist itself increases velocity, NEVER.  What we have said, and have now proved (enough so that Noveske just released its own 12 twist barrel with "modified" chamber), is that the unnecessarily  fast twist of 1 in 10, when paired with a tight chamber, gives the highest possible pressure environment, in which you could develop 6.8 loads.  These specs hamstring the performance of the cartridge, which is why it is now almost impossible to buy a SAAMI chambered, 6 groove,  1 in 10 twist barrel (thank goodness).

When we used what the designers intended, we found that we could load to velocities which were higher  (and these are confirmed with a pressure transducer)  given the same load recipe, in only certain spec barrels, specifically designed to allow lower chamber and barrel pressures.....and you are surprised by this??

IOW, you could use the 12 twist, 3 groove , DMR chambered gun and get, say 2900 FPS  with a load that generated about 55,000 PSI in that gun, but when that same round was fired in a 10 twist, 6 groove, SAAMI chamber, it generated 62,000, deep ejector swipes and was then considered to be over-MAX.

Please read the performance tests before you tout your expert 6.8 knowledge here, OK?


ETA:  I edited a couple of numbers based upon my notes from the test, since we did not publish the TSX velocities initially, as we were asked by Art from SSA not to divulge data on this then- prototype load.

Exactly where and in which post did I mention a 6.8 using a 110g bullet moving at 3200fps???  Either here or over on 'the high road'???  For those of you that want to see that thread also: http://www.thehighroad.org/showthread.php?t=380279&page=2.

I never mentioned a 110g bullet going 3200fps.  I showed you and anyone else the link to the testing done this past summer on various 6.8 barrels using various factory and handloads of the 6.8 SPC.  The charts not only show the velocities of the various barrels, but also the measured chamber pressures.  If they or anyone else would care to read a little, the data also includes photographs of case heads to show what if any pressure signs do show up.  There are lovely graphs and 'all' the information, good or bad!!!  No findings were hidden to skew the results.  It just sounds like you have a certain agenda here and over on the other forum.  You seem to want to attack people that have valid information and yet, all anyone hears from you is 'what you think'...We'll let the people here and on the other site decide for themselves.

That sounds more like reality to me.

No you didn't say there was a 3200fps loading this guy did.



You did however jump right in to argue on his side. This was at the bottom of page one and is the load in dispute. Your data was given in defense of it even though it contained no such dangerous loads.

Let's also make sure everyone understands some other things:

1) The loads now being developed for maximum velocity are put together by reloaders with up to 30 years experience.  Theirs' far eclipses mine, so I depend upon them ( Tim W, Constructor, others) to guide me when I started to build compressed, hot loads.  Thus far, I have remained safe and the pressure tests helped me confirm just exactly what an "ejector swipe" actually translated into w/r/t pressure.  It is nowhere near 80.000 PSI!  The hottest "proof" load we fired, went up to about 69,000 PSI and as you would guess that is from the DPMS, with the tightest chamber and fast 1 in 10, 6 groove twist rifling.  We knew this would be the case.  The 18" 12 twist 6 groove shot that same load at 60,000.  THAT IS 9,000 PSI difference!!  

2) I do not fire that 110 grain SPH load with 32 grains of H322 in my CA gun.  I have broken them down and will cut back by 1/2 grain to try them in my 12 twist, 3 groove.  If they show significant swipes, then I know I am probably just over 58.000 and will cut back more.  This is what you should do, too.  Do not depend upon what you see here on the 'net, or in my or anyone else's posts until you read the test results, consult manuals, decide upon the starting and likely maximums, and only then load them for yourself.

3) the bottom line is that we NEVER intended for this performance test to be a guide as to how you, or anyone else should load ammo.  Rather, it was to illustrate the way, and the degree to which twist rate, rifling dimensions and design, and chamber could affect pressure in a single load.

That is all....

OK I rescind my original statement. If these differences in dimensions and pressure ratings cannot be reconciled with SAAMI then 6.8 will go the way of the dodo because you'll never see 6.8 rifles from the big four in quantity enough to keep 6.8 alive as anything more than an obscure niche round (think 307 win or 7-30waters).

WRONG.

-5.56 and .223 also have three chambers.

-.223:  creates highest pressure because it is tightest with least freebore.

-5.56 NATO: allows for more freebore and thus more widely varied, hotter, Mil-Spec ammo

-Wylde chamber:  combines the attributes of both for greater accuracy and safety with mil. ammo.

ANALOGY:

-6.8 SPC originally was released with SAAMI drawings analagous to that of the .223.  SAAMI spec Rifling dimensions WERE IGNORED by major Mfrs. who used 6 groove, rather than the specified 4 groove rifling, simply because .270 Winchester used this design.  They are different cartridges, right?  5R, polygonal and 3 groove designs lower pressure even more due to reduction of engraving / bearing surface area contact.

-The SPCII chamber is analagous to the 5.56, and is compatible with hotter loadings and bullets which might obturate in the chamber, not the bore, like the old X-treme.  Longer bullets, like the 115 SMK, with a bigger shoulder, get a little more play.

-The DMR chamber combines elements of the other two but with gentler forcing cone  angle and enough freebore to allow hot loads with better accuracy.

ANALOGY 2:

How many different .308 chambers, and rifling designs are there?  Has this hurt the ubiquity of the cartridge?  I don't think I need to go any further.....

Uh huh. Does the SAAMI .223 chamber dominate discussions on this site? Nope. Everyone wants the non-SAAMI 5.56 or Wylde chamberings.

Noveske is moving to a SPCII 1:12 twist poly barrel for ALL their 6.8 offerings.

WOA already offers SPCII 1:11 twist barrels.

Stag is moving to a SPCII 1:11 twist for ALL their 6.8 offerings.

Rock River is already SPCII 1:10 twist, and is considering the move to 1:11

DPMS continues to use a tighter than SAAMI 6.8 chamber, but is moving to a 1:11 twist. DPMS does the same thing with their .223 and .308 rifles - very tight chamber as a way to improve accuracy on rack grade barrels. I'm guessing DPMS will not move to a better chambering because of what they continue to do in their .223 and .308 offerings. However, it is very easy to have a DPMS CrMo or SS barrel reamed to SPCII or DMR chamberings.

Armalite is aware of the SPCII chambering, but the LRIP initial 6.8 uppers are SAAMI 1:10 twist.

Who the hell knows what Bushmaster is doing.

Again, 2009 will be a telling year in the 6.8SPC story.

hi-tech-rancher,

Thank you for you superb posts that accurately describes the capabilities of the 6.8 mm.

A lot of people posting about this topic are spewing forth inaccurate speculation; you are providing verifiable facts––too bad more folks don't pay attention to the details before hitting their keyboards or opening their mouths...

coke is better than pepsi, pizza hut is better and dominos, bud light is better than miller lite. chevy is better than ford. Does all this sound stupid? Why is it that every time this discussion comes up it turns into a 2nd grade pissing match. come on guys grow up. To each is his own.

but even in it's worst possible chamber ammo mismatch .223/5.56 doesn't cause the patently unsafe conditions that you mention from 6.8spc. You guys need to look outside the narrow world of specialty AR uppers at the larger picture. Without multiple big name ammo and firearm manufacturers stepping up to the 6.8spc bandwagon due to non preforming SAAMI specs this cartridge is doomed in the long run.

It's one thing to have variances in chamber dimensions that cause a mild increase in pressure or a slight decrease in accuracy. It's else entirely for these differences to shoot pressures thought the roof. Again I stand my my statement that if these issues aren't sorted out 6.8 will have trouble staying alive long term.

Remember new cartridges are being introduced literally almost everyday, it's only a matter of time before some manufacturer introduces another AR15 round that replicates 6.8's abilities and does preform from the git go and has none of this baggage.



and how many of these chambers avalible in production rifles cause pressures to spike close to 10K psi when factory 308 is fired in them....I don't think I need to go any further...

I give up....I have posted links to data.  HTR has given data and useful information.  DocGKR in previous postings has given links to various 6.8 data and government/industry reports/tests.  Tim_W wrote the extremely long and thorough test report after spending his own money for the pressure transducer test equipment to give accurate and real data.  The guys over on 68forums.com have spent countless years (total experience) testing and evaluating this round.  Hunters are taking deer, bear, hogs, antelope, elk, caribou, coyotes, and bobcat.  Remington, Hornady, Silver State Armory, Corbon, and Double Tap are making ammunition for this round and there might be others I forgot.  Manufacturers are now producing this rifle in Spec II chamber's along with slower twist rate barrels.  The only major manufacturer of AR rifles not offering this caliber is Colt...

To answer the OP original question...no one knows the future!!!!!  If I were to give my own guess, I would say that this round probably will be here for a couple years.

come to 68forums.... classes start early and end late....  

Big four, you mean the Beatles? I thought there were only 2 or 3 of them left, not four. Anyway it doesn't matter, you're right, the Beatles never reconciled either and pretty soon they will be extinct too just like the dodo and everyone else on this forum.

Seriously, Elvis has left the building in this conversation. Please explain in your own words how the 6.8 will go away when it offers the performance gains in the standard AR platform that it does. And again most of the major manufacturers have 6.8 products that are selling quite well. The original SAAMI specifications for this caliber were too restrictive for the 6.8's performance capabilities. So you're saying no one is allowed to improve their products?  

Just because enterprising individuals, and manufacturers figured this out and improved their product to release the true potential of the 6.8 it is now going the way of the dodo? Come on.  So I suppose the airplane is going the way of the dodo also since all airplanes are so different from the original Wright Flyer specifications? Thanks for the stock tip.

Note to self.... Sell Boeing stock.    

Specialty uppers? You mean Noveske, White Oak Armament, Denny's GTS, JTAC Supply, AR15Performance, Addax Tactical and others.

Big name ammo? That would be SSA, Hornady, Remington, S&B

Big firearms manufactures? You mean like Armalite, RRA, DPMS, Bushmaster, CMMG, LMT, LWRC, Remington, Stag, Robinson Arms

Yep the product is doomed.

In all seriousness, if you want to find out more about the 6.8SPC, or the 6.5 Grendel, I highly recommend you visit 68forums.com, or one of the Grendel forums and make up your own mind. AR15.com is one of my favorite forums, but sometimes the discussion ceases to be a discussion and nothing comes from it. This one is an example as evidenced by Moderator involvement.

My 6.8 SPC LWRC with 10.5"bbl, polygonal rifling, 6 groove and SPC II chamber is without a doubt my most fun gun to shoot.

Anyone who shoots it, shares the same opinion.  

Personally, I think 6.8 is here to stay.  It's just better than 5.56....except for the cost.

2 unasked for cents,
Sean

PS.  I ask this in almost every 6.8 SPC thread like this....but no one answers it.

Does the DMR chamber lessen the reliability of 6.8 over the SPC II?  I am purely guessing that one has a tighter chamber and is therefore more susceptible to a malfunction.....but is probably also more accurate b/c of this.  

Any opinions?

PRAISE GOD SOMEONE FINALLY SAID IT

I'm still amazed at the 6.8'ers flying off the handle for merely pointing out these issues MUST be resolved so all manufacturers can be on the same page to help insure long term viability of this round. The very thing you're actively trying to do.

The very data that's been thrown about for the purposes of this thread clearly shows that a "bad" gun ammo combination gives pressure increases close to 10K. Now don't you think that's a serious problem that needs to be worked out?



yes, not any longer and yes

+1

How nice.  I see common ground is indeed possible

To answer your fist question, YES.  It is apparent that if you ask someone that doesn't know much about the 6.8, their first inclination might be  "oh, you mean the one that has pressure problems with certain ammo...?"  Or, "...I don't know anything about the chamber and twist and I hear that's important..."

What we have tried to do is simply help manufacturers see that the SAAMI guidelines  helped to worsen the problem rather than to solve it.  The barrels you will see in the future are being tailored to ensure that these pressure problems are behind us.

Remember:  Even the Ko-Tonics / Cardinal Armory barrel, which was thought to reduce pressure via the 11 twist, 4 groove, and SPCII chamber, eventually got lumped into this category, not because of any problem with those specs, but because of an unforeseen issue with chroming.

That is, when they were chromed, the lining was applied too thick and bore diameter was smaller than (and this is SAAMI spec)  .001" off.  Many came out smaller by .002 or even 003" and blew primers with "standard" commercial pressure loads.

So, there are many things which must be worked out with new platforms and especially when sales are so astronomical that even an ethical, honest business man like Tim Hicks just finally couldn't keep up enough to hold QC perfect.

Robust sales of existing guns and increasing demand is the only thing holding up the manufacturers from transitioning to the 11 and 12 twist and the new chamber.  You can understand why they would want to sell everything else they have first.

ALL of these issues simply are Growing Pains.   Look at Noveske, Lothar Walther, Charles Daly,  Stag (the new hunting rifle with 11 twist, 4 groove rifling and SPC II chamber looks really great) WOA / Denny's and you will see where these people are headed.

IMO, that bodes REALLY well for the future of this cartridge.

Good question Sean. I spotted it. I'll find one of our chamber experts to  give you a detailed answer. I know both can be very reliable, but you are looking at them as match chamber versus combat chamber comparisons. Or feel free to visit 68forums and post your question there also.

Last I heard, SSA is the only commerical ammunition supplier making rounds hot enuf to be possibly of concern in the original barrel offerings, and, before they will sell you their "combat" loads, you must inform them of the barrel/chamber configuration you are planning  to fire it through.

The owner is expected to be intelligent enough to tell the truth.

Actually the DMR chamber in some ways is actually more reliable as certain specs were changed to allow for a smoother bullet transition into the bore. that said it does reduce some of the slop out of the SAAMI/SPCII chamber in very specific areas but it still allows more then ample room for reliably shooting even with very high round counts.  By reducing some of these areas it increases case life and increases accuracy, a few changes decrease pressure even further then that of the SPCII and causes less bullet deformation. Now I can not say if you were to fire thousands upon thousands of round or need SAW like full auto capabilities but short of that its very reliable and in some ways more so while also increasing accuracy and decreasing pressure.  

But the fact is the SPCII does have more room and if you had to fill both with a bunch of crude the SPCII becasue of that extra space it would seem it would function longer. Whether that would play out that way in the real world I am not sure but can say both are very reliable.

When it comes down to it I guess its very much like the Wylde or Noveske Match Mod chamber that are used for the 5.56

Also none of this effects headspace etc you can use th same bolts for SPCII SAAMI DMR  same with depth as at the spec COAL none of the bullets are close to touching and the dif in leade between the SPCII and DMR is .005 with the SPCII being the longer.

SAAMI is for sheep

I am not taking any cheap shots at what you posted, but you are stating chamber pressures that are apparent due to this or that characteristic.

Show me the pressure rig test data please.

6.8SPC performance report with pressure trace data

Thanks very much for the input guys.  

Obviously, I have a 10.5" SBR 6.8 so I'm more concerned with it going bang everytime I pull the trigger than I am with the accuracy at any great distance (though it would be nice to have both).....which is why I asked the question.

I just wish LWRC had looked into using a 3 or 4 groove bbl instead of the 6 groove, polygonally rifled one they went with as from what I gather, it would seem to be a better match to the ultimate capability of 6.8 especially with a 1:12 twist over the 1:10.

Unfortunately, with a proprietary piston system, I have no idea how hard it would be to switch bbls or if it would even be of any advantage in an SBR like mine.   This is probably a better question for the 6-8 forum than here anyway.  

Regardless, I'm tickled to death with my 6.8 and if all the mfg's can get on the same page in regards to the best spec chamber, bbl twist and groove number....I think the 6.8 will really be a great cartridge (even better than it already is).

Thanks again for the input as well as all the hard work guys like Tim W, hi-tech rancher, DocGKR (pelase forgive any mispellings and those I left out) have put into this cartridge to make it all that it is and all that it's capable of becoming.  

Some of us greatly appreciate your efforts and really appreciate the knowledge and experience you bring.  I'm a complete moron when it comes to anything to do with reloading, but I'm benefitting from what you guys have pioneered.

Thanks.

Sean

I am not taking any cheap shots at your post, either, but if you have really read up on the 6.8, you would probably have known that our first test was posted, and is tacked, as of March 2008.  The second, and much more exhaustive test was performed in August and is tacked also.  It includes comprehensive pressure trace data as it regards all the various combinations of specs in barrels that can be bought.  

Link is provided already.  Please peruse it and then come back and feel free to log any feedback in that thread, as posting it here would amount to a hijack of sorts.

I know that some of you are still naive to the evolution of the 6.8 SPC, so if you will just read the performance test, it covers the history of the original design, the disastrous Remington attempt to release the cartridge commercially, and now the repair of that damage by regular shooters, reloaders and folks like Tim Hicks / Cardinal Armory, DocGKR, Constructor, Tim W, Art Kalwas at SSA, and others.

+1 on the anal retentive nature of bill alexander's desire to take credit for a cartrige designed by lapua.

EDITED, PLEASE READ THE Code of CONDUCT, Knocking a poster due to lack of knowledge or low post count is verboten here ~ Cold

I own both chambers and never a FTF or FTE with properly prepared brass.the one FTF I have ever had in either was because i forgot to trim brass after third firing.

The 6.8 has growing pains, lets see the 5.56 is it a 1-7 or a 1-9 or wait a 1-11 twist I can't remember or is it all of the above. Know your weapon and what it can do.

Art - SSA

Ok we all live in this fast paced want it know time ,  BUT let us try to remember that not everything has been correct right away.  Seems to me that the great 223 in the AR frame had teething problems that caused more than its share of wounds or deaths. ask any on the Vietnam vets from 65 thru 70 how they liked there plastic mattie matell toy rifle????? and now the M4 is the standard that many are comparing it to. I do believe that our beloved AR frame is about 45yrs old!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! and has gone thru quite a bit of improvements on its life span. the 6.8 is just a take off of it but a BETTER round all together. the 308 in the M14 did not do well in the tropics of the Asian area, until they got the synthetic stock there were warpages that thru off the accuracy. the M1 Garand born in 1935 had a few teething problems until 1940 when it came on its own as the greatest battle rifle ever. we could go on and on, but the bottom line is when our military leaders finally decide to take on the buraucry and put there foot down and DEMAND that our soldiers have the best round available, and the cost is low for a replacement upper to marry up to there lowers , we will finally see that the 6.8 IS the round of choice, and personally I think that they should tell NATO to take a flying leap with there requirements for universal rounds. when will WE stand up and say we are going to use anything that WE want and require to keep our soldiers safe. and one last thing, how many of you know that the United States NEVER did SIGN the nato agreement on the use of specific ammunition. we just went along with it. WE DO NOT HAVE TO USE 223 or 308.
sorry this is so long but with a daughter in the Air Force , and a son in Afganistan right now, this Nam vet is just sick and tired of cow tailing down to the few that trys to set our laws .

Or is it 1-12 or 1-14?  
Anyway I have a LMT MRP 6.8 what twist and chamber is it?  I shoot SSA and have not had one problem with it.  I like the 6.8 I also like the 6.5 but for different reasons.  That said my go to is still a 5.56, with TAP 556. I wish both 6.8 and 6.5 ammo was cheaper and more available, but untill them the bulk of my shooting will be the mouse round.

I agree. It would be nice to see ammo prices come down a little. Wishful thinking huh?

LMT MRP 6.8 rifles have the 'standard' SAAMI chamber and 1:10 barrel twist.

I keep writing and asking for them to change to the Spec II chamber and at least 1:11 twist...