6.8spc twist rate

bluealtered

New member
Ok, i been bitten, ... i'm going to do a 6.8 kit. I see that some consider the 1:9.5 twist to fast and that the 1:11 is best. Then i read that the 9.5 is ok with factory ammo, just not as many fps as the hot loads. I'm not looking for 3000fps, just want good groups at the range and to be able to knock down my elk this winter.

Since i have no clue which is right, i need some help from you guys who do know, Please! blue
 
Go with the 1:9.5. If you ever want to shoot the Barns 110gr. TSX or any of the "soon to be released" bullets from Nosler or NwCP you will need the faster twist. We have test barrels in both and can not tell any difference in max velocity. Barrel length in this cartridge DOES make quite a bit of difference in velocity.
John
 
Quote:
Go with the 1:9.5. If you ever want to shoot the Barns 110gr. TSX or any of the "soon to be released" bullets from Nosler or NwCP you will need the faster twist. We have test barrels in both and can not tell any difference in max velocity. Barrel length in this cartridge DOES make quite a bit of difference in velocity.
John



Hmmm, I wonder why the guys over at the 6.8forum get
considerably different results, in their barrel twist
tests? According to the experienced 6.8 shooters, the
1:11 twist has no problem stabilizing the 115 gr. Barnes.
The faster twist barrels do show signs of pressure,
sooner, as development load charges are increased. But
if one isn't pushing for max. velocity, then barrel
twist rate isn't a big issue. Also, chambers like the
SPC II, and the DMR, allow for higher velocities, before
signs of pressure over the orginal 6.8 SPC SAAMI chamber,
again according to the testing done by the "experts" at
6.8Forums. From what I can glean from those discussions,
the SPC II chamber is the most important change to get
higher velocities, or to even shoot "combat" loads, from
Silver State. As soon as RRA makes good on a 8 to 12 week,
now 12 to 16 week promise, which is actually now 20 weeks,
for a 6.8 SPC upper, I will get to actually run some of
the "expert" discussion, through a real barrel. When
it gets here, it will be a SPC II chamber, in a 1:10 twist
barrel. This will probably be the last RRA assembly
for me. I have grown weary of the "We are waiting on
barrels, and flash suppressors" lie. They are making
6.8s for dealers, they should be making good on promises
of 8 to 12 weeks...Heck I would be happy if they made
good on the second 12 to 16 week promise /ubbthreads/images/graemlins/angry-smiley-055.gif

Squeeze
 
All I know is that we MUST only load to current SAAMI specs in our production ammunition or risk loosing our liability insurance. Our 1:9.5 and 1:10 barrels will stabilize the 115gr. Barns TSX, our 1:11 will not. We get a key-hole past about 150 yards. All four of our test barrels are Kreiger with SAAMI chambers and transducer cuts. IF the design of the SPC II chamber gets standardized and submitted to and approved by SAAMI, then we will consider it. In all reality, I do not see us loading to 65,100 PSI in this cartridge as has been suggested.
John
 
Bluealtered,

I have also been eyeballing the 6.8SPC and I have been loading and experimenting with a friends 20" 11 twist chromelined Kotonics barreled upper that I built.

I am not as up to speed on the latest developments that some over at 68Forums and ARFCOM are, but I can tell you this. So far the whizzbang 6.8 cartridge is showing me little in the way of whizzbang. There are calibers out there that will do a better job for a hunting application than the 6.8, at least at this point of the game.

Keep in mind, the 6.8 was intended to replace the 5.56 military round and it had to fit current 5.56 mags and run full auto using high capacity mags.

While I do know the SPC provides some ballistic superiority over the 5.56, it is still not at the performance level of say a 25WSSM or as Mike Milli now is playing with, a 358WSSM.

I would try to steer you into another direction and for Elk, the 25WSSM, 6.5WSSM, AND 358WSSM would be of much better choices.

If the only reason the 6.8 catches your eye is due to the military concept idea then go for it, but for the money spent and all the controversy over which twist and chamber diemension yaddy, yaddy, yaddy, I beleive, at least right now, that even the 6.5 Grendel would be a better choice.

From all the postings I've seen, Grendel barrels shoot real well right from the start. I have, however, no personal experience with the Grendel, but I do have trigger time behind two of the 6.8SPC's I have built and load for. I still believe that the Grendel will cause you less stress in the long run and you'll have a very good shooter right out of the gate. The comparisons between the SPC and the Grendel are far too close to say one is truly better for hunting than the other.

Otherwise the WSSM calibers are still far superior to either and feed very well using slightly modified 5.56 mags. I have never had one single failure to feed or extract while using my 243WSSM upper. I have well into 500 to 600 rounds thru this thing and it still shoots awesome groups.

My advice............. bottom line, talk to Dan Carey or Mike Milli before you put your money into something that is still not as refined as the WSSM calibers. Someday the 6.8 may come around and be the finest military caliber of all time, but today, it just ain't there and for hunting, the WSSM's flat out kill the 6.8 in performance.
 
I looked into it several years ago before the SPCII chamber got thought up, other than it can be shot in a AR I saw no advantage over the 270 WSM bolt action Savage rifle I already have, in fact it came up short in several areas (on paper anyway) instead i opted to build my AR in 243 WSSM instead. I am very plaesed with that.
 
All of my builds to date have been on 1:10 twist tubes. They have been producing fine accuracy from the bottom to the top of the bullet line-up.
 
I've been shooting a 20" 13 twist 3 groove for about 2 months, we just finished a test to check pressures of high performance handloads and twist to stabilize usable bullets in the 6.8. I shot everything up to the 130 Sierra SBT, the Barnes 110gr TTSX which is longer than the TSX the 105gr GS SP with a BC of .505 out of this 13 twist at sea level with no issues. I do not know if it will do the same if the temp was zero but it will stabilize the same bullet at 4500ft and 50 degrees.
We have been getting 2950fps from the 110 Sierra pro-hunter at 58000psi, the 80gr GS HV 3375fps, 90gr Hornady TNT 3150fps all from this 20" 13 twist and all at 58000psi or under, I get 12 loads on the SSA cases.
Every major AR manufacturer except colt makes a 6.8 how many make the WSSM?
 
Stange, Art at SSA loads combat loads that push the 110 pro-hunter to 2700fps and the TSX to 2680 from a 16" barrel and they stabilize fine in my 13 twist maybe your not pushing them fast enough. He is supplying the military with most of the ammo they are testing with.
He has to use the mk262 powder because of the flash suppressant but we can get more velocity with less pressure from over the counter powders. For a mass loader 335 or 2520 works pretty well but nothing like 10X or Norma 200 with the light bullets.
 
Welcome to the PM constructor!

Shilen only offers a 10 twist in the .270 bore. If they produced a little slower twist, I would love to try it, but the market just isn't there, and I don't see them producing another twist in that bore.

I don't know exactly what you meant in your final line about the WSSM. I think the WSSM is like some of the other calibers offered only by custom shops or a few manufacturers. The market is always going to be small in comparison to the .223 or even the 6.8 SPC. People looking for way more energy, and a much flatter trajectory than the 6.8 is what my customer base is built on. The WSSM line fills that need very well.

Back when Oly was working on getting the WSSM line off of the ground, we talked about other companies perhaps producing a WSSM AR. It was Oly's thought that the market would be small enough that no one else would go through the expense to fight for the relatively small market. To date, they have been correct. Oly is the ONLY AR manufacturer, as you undoubtedly know already, that produces the WSSM or the parts to make it. Building the WSSM's is pretty much a full time job for me, and there is not a week that doesn't go by that I don't have someone call and try their best to purchase WSSM parts from me. It has a small and very loyal following!
 
Quote:
Welcome to the PM constructor!

Shilen only offers a 10 twist in the .270 bore. If they produced a little slower twist, I would love to try it, but the market just isn't there, and I don't see them producing another twist in that bore.

I don't know exactly what you meant in your final line about the WSSM. I think the WSSM is like some of the other calibers offered only by custom shops or a few manufacturers. The market is always going to be small in comparison to the .223 or even the 6.8 SPC. People looking for way more energy, and a much flatter trajectory than the 6.8 is what my customer base is built on. The WSSM line fills that need very well.

Back when Oly was working on getting the WSSM line off of the ground, we talked about other companies perhaps producing a WSSM AR. It was Oly's thought that the market would be small enough that no one else would go through the expense to fight for the relatively small market. To date, they have been correct. Oly is the ONLY AR manufacturer, as you undoubtedly know already, that produces the WSSM or the parts to make it. Building the WSSM's is pretty much a full time job for me, and there is not a week that doesn't go by that I don't have someone call and try their best to purchase WSSM parts from me. It has a small and very loyal following!



I don't know why Oly hasn't pushed that mid sized platform other than they are swamped with the 5.56 stuff. A 6BRX sounds pretty good, I have a bolt here just never received the WSSM upper to salvage so I could build the BRX. A bigger bolt for the 6.8 and 6.5 would be good too. I just see a whole line of things they could do with that size bolt.
I didn't know you only used Shilen, they make a great 6mm barrel, I have a few.
The last line was in response to the guy that said the 6.8 wasn't refined yet, I believe I saw an article saying it's the hottest new caliber for deer hunting and we all hog hunt at night with them, nothing like ambushing a dozen hogs in the dark. We're getting close to 243 velocities from the lighter bullets using the same length barrel of course.
 
Last edited:
Oh no /ubbthreads/images/graemlins/smiliesmack.gif here it comes, the battle of the 6.8

Constructor has done a good deal of improvement on the original 6.8SPC. He and a handful of others on the 68Forums are testing everything they possibly can to provide barrel twists, chamber diemensions and load development to improve the performance of the cartridge. Unfortunatley many times it comes down to mine is better than yours which is often read on ARFCOM. I certainly hope he and the others can convince barrel companies to change the production of barrel twists and chambers to allow the hotter loads that have been tested. I would love to have a 6.8 that I can trust to handle the pressures and velocities that they seem to be obtaining without blowing primers or creating unsafe shooting conditions. But for now, my WSSM will do my dirty work and it just keeps on getting better.

As I stated in my prior post, I believe right now is not the right time to jump into the 6.8. Let those that are interested in the performance gains make all the adjustments and begin there.

Bullets are no doubt getting better for the 68 and in a year I believe we'll see a few more from top rated manufactures that will significantly improve it's performance in long range and hunting applications. I also believe the powder companies will step up to the plate to offer additional load data.

This is not about who or what is better, it's about options.
 
Quote:
Quote:
Welcome to the PM constructor!

I don't know exactly what you meant in your final line about the WSSM. I think the WSSM is like some of the other calibers offered only by custom shops or a few manufacturers.



The last line was in response to the guy that said the 6.8 wasn't refined yet, I believe I saw an article saying it's the hottest new caliber for deer hunting and we all hog hunt at night with them, nothing like ambushing a dozen hogs in the dark. We're getting close to 243 velocities from the lighter bullets using the same length barrel of course.



That was my line and I stand firm on that comment. Remington screwed to pooch on the SAAMI specs long ago, otherwise the 6.8 would have seen much better ballistics before the stone was carved. It's taken guys like yourself a long time and a lot of money to improve on the 6.8 and with little recognition I might add. There are always going to be publications out there from some writer that is going to say things like "WOW, HOLY Cow, this is the best thing since sliced peaches". Go back and read about the 17HMR.

If it were refined then I would be able to purchase a 6.8 barrel from any company and shoot SSA Combat ammo without fear of it blowing primers or worse. I am working with a Kotonics 68 barrel now and so far it hasn't rocked me into a spastic attack but time will tell. It could be that the one I have been loading for is one of the screwup barrels with bad chromelining, don't know for sure.

Barrels can be purchased but not many companies if any that I'm aware of, are offering what Constructor offers at AR15Performance.com ....You are welcome for the plug that'll be a dollar thank you /ubbthreads/images/graemlins/smile.gif

BTW, Welcome to PM, I'm sure you'll find there are numerous individuals here that are AR freaks and you might just be able to make a buck or two by sticking around.
 
Constructor!!!! Glad you found us!!! Remember this one?

18inPhaseII.jpg

18", 6.8SPC, 1:11 Supermatch, DMR chambered, AR Performance barrel that shoots bug holes out to 250!! Probably farther, but now that the crops are tall, we can't see the berms W-A-Y out there. /ubbthreads/images/graemlins/smiliesmack.gif

Constructor's handy work went into the upper!!! I guess you could say I'm a 6.8 convert!! I know, I know... another plug. This one's on me, H!! /ubbthreads/images/graemlins/grin.gif
 
Last edited:
oh yea, 2 nice rigs I love those POF lowers. I really don't have much time to read through forums anymore, just googled something and landed in this thread.
I didn't post anything about the Texas test yet, but I sent 1 bullet down range at 3412fps. I think Tim was afraid to pull the trigger.LOL
Those GS bullets are nice but too dang expensive to shoot many of them.
The test did prove what we have been saying all along and TimW. may post the test results next week.

Falfire, no battle here, just trying to spead the truth about a refined 6.8 LOL.
I still build 5- 308s to every 6.8 but it's catching up and so is the 260.
I have .277 barrels with 11 twist 4 groove, 12 twist 3 groove and 13 twist 3 groove now and should have 11.25 twist true polygonal barrels by the middle of Sept.
The 6.8 is not the best sniper round or varmint round or big game round but it could be the best round for the military and a fine close range
 
Wecome aboard constructor, i wasn't looking to start a what caliber is better war, simply looking for something shorter barreled than my .270 bolt gun with the same power, and that i could afford to feed.
I burn a couple hunderd rds. a week and about the only thing that fills that nich so far is the 5.56/.223. However it's just a little light for crawling around on your hands and knees in very thick brush, and ending up nose to nose with a gut shot bear. No i didn't gut shoot him, but i was the one who ended up in the reprod finnishing it, somehow that .40s/w just didn't feel big enough. blue
 
Back
Top