6.8 history-

[constructor]

These are links and quotes from the 6.8 past.
Some funny, some telling. Pay attention to the dates of the posts.

Ko-tonics [Member]
10/7/2006 9:26:58 PM MDT
I do.

We had a special finish reamer made by Pacific Tool, the specs for which were given to me by Art at SSA. The barrels are on their way to US Chrome for chrome lining the bore and chamber. We expect them to be done by the end of next week.

Art is sending me some of his combat loads for testing the product. I will be posting results as soon as we have the barrels in, built and tested.

You can read more about it here: The KT68 AR-15 Upper.

Guess that proves Art designed the SPCII chamber

http://www.ar15.com/archive/topic.ht...f=121&t=298490

Ko-tonics [Dealer]
1/23/2007 4:43:39 PM MDT
Okay folks,

I am very hesitant to jump in at this point. I don't think anyone has written anything about the barrels that I feel the need to "correct" or "argue about."

I am having no trouble at all selling the existing barrels, in fact by next week the 16" barrels will be gone, and the 18" barrels will probably be gone the week after that.

I think there are two questions here for which I would like to offer some possible answers.

First, what happens if I (an average AR-shooter guy) get a 1:9.5 or 1:10 twist "average" barrel and I want to shoot "average" commercial ammo in it?

I think it's too easy to throw dirt on the current loading of 6.8mm SPC commercial ammo in the "average" 6.8 barrel. There's nothing "wrong" with it. It has plenty of power!

My favorite point of reference for the effectiveness of 6.8 is deer. Deer are the most popular big-game animal, by far, in N. America. They are nearly big enough, depending on where you live, to provide a yardstick for the relative effectiveness of any particular load and firearm on two-legged varmints. When you shoot a deer with the "weak" commercial 6.8 loads, wonder of wonders, the deer falls over dead! He never has time to ask what the twist rate of your barrel is, or how much lede you have in the chamber. He is too busy becoming venison.

The fly in the ointment is that everyone wants bullets to fly >2,800 fps. Me too! It should be noted that the original goal for 6.8 was to be 300 fps faster than 7.62x39. To do that we need to hit 2,600-2,700 fps consistently. When I talk to you guys that have the average barrel (SAAMI-spec chamber, 6-grooves, 1:10 twist) you're seeing 2,300-2,500 fps depending on the particular ammo and length of barrel.

The good news is that no one is having trouble getting accurate 6.8 loads. There are many, many shooters who are able to shoot sub-MOA groups with the "average" barrel. Most Elmer Fudd hunters with blue steel and walnut bolt guns would swoon if they could shoot that well! About the only guy around who can't shoot an "average" 6.8 load and rifle sub-MOA is yours truly. I have to get my customers to tell me how well they can shoot, because I can't ever seem to get it right...

Now to the second question: How come the "average" barrel/rifle/load doesn't seem to get to the kind of numbers we'd like to see on our chronographs?

I don't know.

I have a few guesses.

Some of my guesses come from reading, some come from hunches, some come from sad experience.

In a nutshell (here comes the history lesson):

1) Someone who will remain nameless botched-up the chamber drawing on the SAAMI specification. You can download the spec from www.68spc.com. Do a little high school level geometry with the dimensions of the lede and throat. The math is wrong. I am no genius and even I can see it.

2) When big name AR makers went to their barrel makers and said, "make us a bunch of 6.8 barrels," the barrel makers said "hmmm, that's a lot like .270 Winchester or WSM. We'll just use the buttons/broaches to make rifling just like those. Yeah, that'll work." And the big name AR makers said, "see, we got 6.8 too!"

3) The premium barrel makers did their homework, read the SAAMI-spec, fixed it, thought hard about rifling, fixed that, and made a lot of barrels for people going to the sandbox, or who otherwise have good reason to dump lot's of cash into a premium weapon. And you can buy a very, very nice rifle or upper from PRI or Barret, and you, too, can get consistent 2,700 fps out of your 6.8 rig.

What? What's that you say? Your wife will find out? You mean you've got bills to pay and mouths to feed and stuff like that? Sorry, I guess we need to come back to earth.

I have hopes about our new barrels. But I won't make any claims until we can test them with real loads and see real numbers on real chronographs. And I hope I can offer a product that will consistently deliver 2,600-2,700 fps with any ammo you want to stuff in it. And price it for "the rest of us."

Until then... We'll just have to shoot deer with our old slow-poke 6.8 rifles and hope the deer keep falling dead without questioning the actual velocity of the bullets.
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hi-tech-rancher [Member]
3/16/2007 10:25:49 PM MDT
I got into the 6.8 SPC 2 years ago, because I didn't think the .223 was adequate for killing south Texas whitetail deer, and the hogs I shot with it ran for hundreds of yards. I have now shot Hornady Vax's, plenty of SSA extreme and Barnes-X's and I can order ammo from one of several catalogs and suppliers.

I LOVE this cartridge. Forget the comparison to 6.5, .223 or .308. This cartridge fills its own niche, and it won't be going away any time soon. I will probably build a bolt gun with a 26" barrel to get the velocity up to around 2900 FPS with my handloads. My 16" M4 shoots V-max's @ 2520 on average, chorono'd. That is good versatility in just one cartridge.

I actually have started to use the SSA extreme for hogs, because the penetration is excellent, and even with FMJ, the 115gr weight is equal to two .223 slugs arriving on the target, and it does kill them. Head, neck or shoulder, it goes all the way through. So does the Barnes, most of the time.

When I had to use my .223 upper for a while on the ranch (while waiting for my optics mounts to arrive for the 6.8 upper) I couldn't wait to get back my "not mouse gun."

My future uppers / rifles will be another 6.8 SPC, AR with a suppressor, and a bolt gun in same caliber. Since I already own a suppressed .308 bolt gun, I am sure that I will someday buy a DPMS .308 AR, but with the 6.8, I am in no hurry whatsoever.

[Force]

Good read H !

Thanks for share'n.

[constructor]

continued-
constructor [Member]
4/2/2007 12:17:46 PM MDT
Finally able to test The WOA 18" 1:11 twist 6.8 stainless fluted barrel this week end.
I just loaded 20 ssa small primer cases. 26 gr reloader 10, rem match primer. 115 sierra match king seated just deep enough to work in the mags. after 3 sighters the first group of 5 went into 1/2" !! No load development. did not use sized cases.
Thats the difference between a production bbl and a custom one made by someone who knows what he's doing.
After over 200 rounds the best I could get out of a production model 1 bbl was 1 1/2"

Who said the 6.8 isn't accurate enough?

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kalwasart [Member]
3/12/2007 10:56:00 AM MDT
You have the old Combat Xtreme's, the Kotonics barrels you have can not handle it, the twist is too fast. The new Kotonics with 1-11 twist - 4 grooves and increase free bore can handle them with no problem.

The rounds you received were designed around a Barrett rifle (only game in town at the time) and it has no problems shooting the Combat Xtremes.

We just tested the new Kotonics and we can throw a brick thru it. Our 115 grain MIlitary/LE rounds are getting 2,560 FPS from their 18" barrel with no pressure signs. We pushed the charge weight to 31.3 grains and got 2,630FPS with still no pressure signs. We will have to go to a faster powder to see what this baby will do.

DPMS just sent us barrels in 16 & 20" lengths for testing. We tested them with our Mil-Spec combat loads the 20" barrel is getting 2,555FPS with light signs of pressure (shine around the ejector), the 16" got 2,541FPS.

Currently we supply several gun manufactures ammo to test their weapons, CMMG, PRI, H&K, Kontonics just to name a few. We only supply combat loads to the Military & LE and those who have weapons that can handle the proformence rounds. These so call hot loads are at 52,000 PSI below SAAMI max. test were done with a 24" test barrel 4 grooves 1-10 twist

Send me an email art@ssarmory.com and we will replace the ammo at no charge with the lighter commercail loads.

Sorry for any problems this may have cause you and we want to make things right.


Regards

Art - SSA
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constructor [Member]
5/2/2007 6:20:31 PM MDT

Originally Posted By AR15barrels:
Originally Posted By hi-tech-rancher:
Of course, this is with the OLD Remington OTM, loaded at higher pressures. Other handloaders probably wouldn't want to try duplicating this with the 1-9.5 production barrels with shorter throats. These figures are what made Remington look so bad, because the SAAMI dimensions they provided apparently wouldn't allow these same results safely. The round is surviving (although in a weakened state) in spite of this foolishness.

"These were all fired in 1:10" twist 4 groove mike rock barrels with SAAMI spec chambers and throats.
No extended throat was necessary and these LE loads showed no pressure signs.
I have more of this ammo that I still use for test firing and I have yet to have any problems.
I just would not recommend running it when the ammo is at 130 degrees.
At normal sane temperatures of 95 degrees, I have not experienced any problems." RR

Thanks for the info. I'm working with 18" barrels now 1:11 twist and my vel are also around 2730-40 with hand loads. 29gr 322 or RL10 and 110 Vmax. I can use the same loads with 115 sierra. I think 30 gr is max with these two powders just because of case capacity.
WOA uses the old style reamer so I had it reamed my self and was able to add .5gr to the charge.

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Ko-tonics [Dealer]
5/4/2007 12:42:55 AM MDT
DO YOU MIND MUCH IF I GO BACK TO THE ORIGINAL POINT OF THIS TOPIC, RANDALL?



For you fans of chrome-lined barrels: The first customer for a 16" upper with my new barrels gave me a report from his first trip to the range today. He said he may have a chance to post something hereabouts in the coming days. His words: "This sucker can SHOOT!" Very encouraging accuracy results. And he bought a few boxes of the old high-pressure SSA ammo from AIM, fired them through with no problems whatsoever.

I have a BUNCH of orders for 16" uppers, and I am expecting to get a lot more feedback in the next few weeks.

The point is, I am tilting strongly in favor of chrome-lined for the 20". If there is no "accuracy penalty" with chrome-lined, then I see no reason not to go that direction.

Thanks for all your feedback.

[constructor]

Randall Roush reamer print by PTG
http://www.68spc.com/68spc-reamer.pdf

link to long thread
http://www.ar15.com/archive/topic.ht...f=121&t=282708

SeanK1ng [Member]
7/4/2006 10:05:04 AM MDT
L-W usually uses ER Shaw for their bbls. I don't know if this is the case for the 6.8 or not. They use Remington ammo for all their testing (although I guess at some point they evaluated SSA, hence the comment below). Their chambers are built to SAAMI spec, but wasn't there a question about the spec being backwards on page 2 of this thread?

Here's what Paul Leitner-Wise had to say about the issue of high pressure and tight chambers:

All our 6.8's run standard SAAMI spec chambers. That gives a neck size of .308" and after chroming this is around .307".

With any semi-auto, you want to have .006" to .007" of clearance at the neck to allow obturation of the cartridge and reliable feed and extraction so ideally, the neck on the 6.8 should be .300" or less. Remington and Hornady are both in the .299" range and we have experienced no problems with either.

The early Silver State rounds had neck sizes as large as .3065", all of these rounds would regularly blow primers, fail to extract or show excessive pressure signs. Both Barrett and PRI adjusted their chambers to suit but we maintain the SAAMI spec required for government use.

We advised Silver State of our findings and understand that the are improving their QA to reflect the desired neck size on their latest production runs.

Provided neck sizes do not exceed .302", you will not have problems.

Based on this response, I'm going to go ahead and order.....any objections?

If L-W is trying to sell the 6.8 to the govt. wouldn't their chamber have to be able to handle the "combat" loads?


Thanks for the input guys. Oh, and can anyone tell me how to access the Armory forum? Wehn I click the "armory" button at the top, it takes me to a different page, but not the forum. Right now, I'm getting to it by using "my topics" b/c I started a post there.

Thanks,
Sean
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kalwasart [Member]
7/5/2006 12:40:10 PM MDT

Randall, check your 6.8 reamer drawing, at the 45 degree angle at the .2781 lead, is it 1.70185? I have received several drawings from different gun manufactures that have that same dimension. But from another gun manufacture I have 1.7109 which I believe is the correct dimension.

If the 1.70185 is being used that means the 45 degree angle can not exist and you will end up with a sharp corner at the lead into the chamber. The X-Treme combat loads needs this angle otherwise pressure will peak.

I have a 5 inch thick file on testing on the 6.8 and have to come to the following:

1. Neck size does not have anything to do with increasing pressure and I have the computerize test result to prove it.
2. Cartridges has to be made to the low end of the spec with regards to dimensions.
3. Recently found errors in chamber reamer drawings developed a sharp corner leading into the chamber, which is effecting the X-Treme combat loads. In the June issue of SWAT the Combat X-Treme had excellent results out prefoming all others rounds. You can blame the X-treme all you want but it works in some guns and not in others, so you decide, is it the ammo or the weapon? We however made adjustments to the X-treme to work in weapons with chamber issues.
3,. If your weapon can not shoot projectiles at 2,650 FPS than you have a weapons problem.
4. Some guns have very bad timing problems, where the bolt is trying to open while still under high pressure. Cases ejecting from the 1 to 3 o'clock position. The hotter the load the bigger the problem becomes.
5. If the case are blowing primers and expanding above .424 (being max chamber SAAMI) this is direct result of the bolt opening early.

Our triple Shock thru a Barrett and CMMG is getting 2,715 FPS, can your gun handle it?

The Military has tested the X-Treme at velocities of 2,625 FPS and had no problems. But again who's weapon did they test it in.

We have made changes to the X-Treme so it will work with all weapons, mainly down loading it. We are try to offer a good round at a reasonable price unless everyone wants to shoot just the expensive stuff.

If I was a gun manufacture I would be asking myself if a round is working in someone else gun why is it not working in mine? Or the quick answer is Blame the AMMO.



Art - SSA

Link to performance report 2008 with reamer drawings-http://68forums.com/forums/showthread.php?t=7220

[Ratdog68]

Inktristink read... my, how the caliber has evolved from "days of old".