View Full Version : 6.8 SPC performance report
constructor
09-05-08, 00:11
the complete 50 page report will be up on 68forums.com within the hour.
http://www.68forums.com/viewtopic.php?f=1&t=3473
That is impressive that they got velocity of 3385 fps out of the 6.8 with an 18" barrel (using a handload with a custom 80gr bullet). That is .243-like performance, and if loads like that can eventually be commercially produced, I would think it would extend the range and lethality of the 6.8.
constructor
09-05-08, 15:04
expect 3 new commercially loaded bullets by spring maybe sooner on 2 of them, 1 of those hits 3200fps from a 18" barrel.
Between now and spring we will continue testing with experimental and foreign powder and bullets.
I hit 3446fps with a 105gr bullet out of a 20" barrel ave of 5 was 3417fps, this was apx 60,000 psi and the cases are fine.
What chamber and barrel twist did you have on that rifle? To get these kinds of performance, does a person have to have that new special chamber and a certain twist rate?
constructor
09-08-08, 16:28
every change from the 10 twist barrel and SAAMI chamber lowers pressure.
so a 11 twist SAAMI would lower presure apx 4000 psi so you could load more powder and get more velocity, A 11 -12 twist barrel with a SPCII or DMR chamber could lower the pressure 8-12000 psi and you could use even a larger charge of powder and get more speed while mantaining the same pressure that the 10 twist SAAMI had.
We are improving the top end performance so we can use stronger loads in short barrels and extend the range that they are effective to.
It takes apx 1700fps for a bullet to expand reliably, if we increase the muzzle velocity 200fps then then effective range of the bullet may be extended another 100 yds.
Cool.
Based on the velocities you've been able to reach, what do you think is likely to be the maximum effective range for the 6.8 (I mean eventually, when some of these experimental loads become standard factory loads)?
constructor
09-09-08, 18:50
Cool.
Based on the velocities you've been able to reach, what do you think is likely to be the maximum effective range for the 6.8 (I mean eventually, when some of these experimental loads become standard factory loads)?
SSAs 115gr "Combat" loads are getting about 2650 from a 16" barrel now that is apx 200fps faster than the Rem. or Hornady. If Art decides to increase the charge again I believe it will be for specific agencies /military only, those groups can control the firearms configuration. There are too many 6.8s out there that will cause dangerous levels of pressure with high performance ammo.
But you can always load your own like we do.
There should be 3 new screaming loads by spring. Watch SSAs site but please don't call and ask when, they are swamped and will not answer until the shipments arrive.
Cool.
Based on the velocities you've been able to reach, what do you think is likely to be the maximum effective range for the 6.8 (I mean eventually, when some of these experimental loads become standard factory loads)?
Not sure what you mean 'maximum effective range'??? Are you using this round to hunt deer? Hogs? Antelope? People???
I believe right now, people are taking deer out 350-400yds with SBRs!!!:D:D
People have taken 450lb cow elk with this round and black bear. So I guess, back to the original question? What are you thinking about it's use?
With the right bullet/powder combination and a DMR rifle of 18-20" it is very possible to make kills out past 600yds. Right now, Constructor has developed loads/rounds that remain supersonic well past 1000yds...sound familiar???
I don't have any experience with this round or the next question.
Anyone have any info on the Ruger mini in 6.8?
Thinking of a semi for deer in a light package, non AR.
I don't have any experience with this round or the next question.
Anyone have any info on the Ruger mini in 6.8?
Thinking of a semi for deer in a light package, non AR.
Mark,
Not sure about the chamber, but the twist is 1:10 so approach the SSA 'Combat' loads with a little caution. They won't blow up the rifle, but, might show signs of high pressure in that rifle...then again, they might not! Anyway, here is a link that I have been thinking about going with when I 'improve' the accuracy of my mini:
http://www.ruger-mini-14-firearms.com/mini_14_30_accessories.php
Here is a good article that Jeff Quinn wrote concerning his experience with the 6.8 Ruger Mini!!!
http://www.gunblast.com/Ruger-RanchRifle68.htm
Jeff is a straight shooter and I appreciate his candor when testing/reporting on various firearms.
Take care,
Kelly
I don't have any experience with this round or the next question.
Anyone have any info on the Ruger mini in 6.8?
Thinking of a semi for deer in a light package, non AR.
There is a good article in this month's SWAT magazine about the Ruger Mini-68. I would summerize the article as saying the carbine was reliable, but not terribly accurate. The author put an aftermarket stock on it and cut the groups in half.
Stephen
Not sure what you mean 'maximum effective range'??? Are you using this round to hunt deer? Hogs? Antelope? People???
I've seen the term used and defined in a couple of ways, but I guess I meant it in this way: the maximum effective range is "the distance at which an individual firing a given projectile at a target has a 50% or better probability of hitting that target."
Have seen the term used in discussions of sniper rifles, but it can be used anywhere.
Here's a few examples:
Discussion of the M82A1a .50 caliber rifle on Global security
(http://www.globalsecurity.org/military/systems/ground/m82.htm): "The optical sighting system must provide suitable resolution to allow target identification at the maximum effective range of the system."
Specs on the M107 .50 Caliber sniper rifle
(http://www.inetres.com/gp/military/infantry/rifle/M107.html): "Maximum Effective Range 2,000 yd (1,829 m)"
RiflesNGuns Online, the L96 Sniper rifle (http://www.riflesnguns.com/article/l96-sniper-rifle): "maximum effective range with a Schmidt & Bender 6 x 42 scope is around 800 m. "
Wikipedia discussions of ranges of various sniper rounds
(http://en.wikipedia.org/wiki/Sniper_rifle#Maximum_effective_range): See table with list of ranges.
In my understanding, it's not some technically precise, scientific measurement, it's just a useful generalization that gives you an idea of how far the cartridge is likely to still be able to get the job done.
There is a good article in this month's SWAT magazine about the Ruger Mini-68. I would summerize the article as saying the carbine was reliable, but not terribly accurate. The author put an aftermarket stock on it and cut the groups in half.
Stephen
I saw that last night, I noticed that they didn't specify the distance. I did read the Gunblast one online and that looked good. In reality, 2" isn't bad in my book. He had the one at 3/4".
Mark,
Not sure about the chamber, but the twist is 1:10 so approach the SSA 'Combat' loads with a little caution. They won't blow up the rifle, but, might show signs of high pressure in that rifle...then again, they might not! Anyway, here is a link that I have been thinking about going with when I 'improve' the accuracy of my mini:
http://www.ruger-mini-14-firearms.com/mini_14_30_accessories.php
Here is a good article that Jeff Quinn wrote concerning his experience with the 6.8 Ruger Mini!!!
http://www.gunblast.com/Ruger-RanchRifle68.htm
Jeff is a straight shooter and I appreciate his candor when testing/reporting on various firearms.
Take care,
Kelly
Interesting stuff there, I'll save that to favorites.
I think in alot of areas we should see some serious headway with the 6.5/6.8 and maybe even other piston systems and other calibers in Shot.
this makes it sooo tempting to build a 6.8 with a 1 in 12 twist rate!!!
but this set up would make for a "killer" mid length with a 16inch barrel!!!:cool:
I don't have any experience with this round or the next question.
Anyone have any info on the Ruger mini in 6.8?
Thinking of a semi for deer in a light package, non AR.
If you like a minute of man carbine, then the Ruger will be great... accuracy is interesting to me and my Mini sits in the ranch safe... I only keep it because my father gave me it on Christmas long time ago. Otherwise it would be sold.
I have one of Constuctor's 18" stainless DMR barrels
great gear by a standup guy
http://lh6.ggpht.com/HammerheadbikesInc/SF74PO9TsbI/AAAAAAAAATY/V5E9dQ0-rKQ/s720/coker-6.8.jpg
If you like a minute of man carbine, then the Ruger will be great... accuracy is interesting to me and my Mini sits in the ranch safe... I only keep it because my father gave me it on Christmas long time ago. Otherwise it would be sold.
Cold,
Did you check out this link for improving accuracy of the Mini???
http://www.ruger-mini-14-firearms.com/mini_14_30_accessories.php
If you could get the correct barrel chamber/twist in one of their barrels and have your Mini bedded by them, it would probably improve your MOMan to MOA:D:D:D!!!
Take care,
Kelly (Cohibra45)
There are also a lot of Mini-14 experts, and smaller steps you can take on your own to accurize the Mini, if you don't necessarily want to go to the expense of sending it to Accuracy Systems and having them rebarrel/rebuild it. They do great work, but a lot of Mini owners (I've owned them before, though I recently sold my last one) find that they can do some less expensive, intermediate steps to improve accuracy, and for a lot of them this is enough. For example, just doing a few simple steps such as re-torquing your gas block, free-floating your barrel, bedding the action, and attaching a tuning device such as the Accustrut (http://www.accustrut.com/) (you can easily attach this yourself) can improve the Mini's accuracy down to perhaps consistent, 2" to 3" groups at 100 yards. You understand, I'm not RECOMMENDING the Mini, I got out of them myself because I think they are frustratingly inconsistent. But for someone who is determined to own one, some of these steps can help with the accuracy issue.
Check out the Perfect Union Mini-14 forums, and see their sticky items for accurizing a Mini, and if you have questions, ping the user named "Cajungeo". He is like the Mini expert of all experts on that forum, and is a nice guy to boot.
http://www.perfectunion.com/vb/forumdisplay.php?f=86
the complete 50 page report will be up on 68forums.com within the hour.
http://www.68forums.com/viewtopic.php?f=1&t=3473
Constructor, any chance at someone posting it here? I really don't want to have to register at yet another forum - already on about 25 of them.
Boltgun
I have always thought a 100gr bullet, moving at about 3000fps, out of a 16" bbl would just about perfect.
Anyone know if such a thing exists?
Well I don't know about what the guys who are pushing the envelope with the 6.8 are doing to get close to those specs you're asking about, but there are some guys getting pretty close to those numbers with .243 loads. There are competitions shooters using bullets in say 107gr that are getting right close to 3000 fps with certain loads, you can read up on it at the 6mmbr site on the .243 page (http://www.6mmbr.com/243Win.html).
I've always wished there were more people looking seriously into the .243 and the AR platform.
Well I don't know about what the guys who are pushing the envelope with the 6.8 are doing to get close to those specs you're asking about, but there are some guys getting pretty close to those numbers with .243 loads. There are competitions shooters using bullets in say 107gr that are getting right close to 3000 fps with certain loads, you can read up on it at the 6mmbr site on the .243 page (http://www.6mmbr.com/243Win.html).
I've always wished there were more people looking seriously into the .243 and the AR platform.
I understand the frustration with the .243 but then, we are talking AR-10s vs AR-15s. That is a huge difference in weight, not to mention recoil!!! The whole reason they are doing the research on the 6.8 is because it is such an efficient cartridge in that platform and it is readily available to the general public.!!!;)
I didn't mean that to suggest I'm against the development of the 6.8. I'm all for it, and in fact plan to buy one, once the market seems to settle down a bit on which chamber, twist rate, and ammo combination is the "optimal" way to go. After the recent issue that Ko-tonics had with their barrels, it made me a little leery and I decided to wait maybe another 6 months before I take the plunge. But in any case, I'm all for 6.8 especially for the reason you mentioned, that you can run it on the standard AR platform.
But I still see value in developing the .243, especially due to its long-range characteristics which give it some nice aspects, with lower recoil than 7.62 but better performance in the wind.
HTR on the 68 forums is getting 2700 fps out of a 16" barrel using the Barnes 110x TTSX and has shot a few hogs with it, complete penetration and one shot kills at over 200 yards
I have the 18" barrel and should be getting a little hotter than that
We are asking Barnes to come out with a 90g TTSX, that little sucker would zing:)
I like 243s, I have a 59 Sako that my 11 year old is now using, it's a tack driving, deer killing machine..
but, you have to do it in heavier AR10
For those that don't want to join 68forums.com, here is a link to TOS...ARFCOM:
http://www.ar15.com/forums/topic.html?b=3&f=121&t=369145&page=9
You don't have to register to view that thread. Caution, if you have dial up, it will take a long time to load as the report is over 50pages long!!! However, it really is well worth the read!!!!!!!!!!!!;)
You can just download it as well: http://m.b5z.net/i/u/6132121/i/6.8_20SPC_20Performance_20Testing_20Report_1_.pdf
OK I have asked this before to some of you. Help me understand the twist rate over at Cardinal Armory they advocate the 1X11 twist with Spec II chambering. Most if not all, Noveske, LMT, Stag and Bushmaster are staying with the 1X10 twist and hopefully the spec II chambering. MSTN and a few others will build for you but I am a poor working plummer. : (
Some manufacturers state it's only the spec II chamber that's important and the rate of twist is not important. Tim at Cardinal Armory said it's important, twist rate. Doc if your listening make it so a 5th grader can understand.
It was mentioned that SSA combat loads may not work in the 1x10 twist because of the pressures built up. Thanks for the info.
I heard a rumor Noveske is changing to the spec II and going with a 1 in 12 twist.
Word on the street is there's 1 or 2 more larger companies to follow along.
Back in the Summer of 2002 when 6.8 mm was selected as the best caliber choice from among the available ARC options, both Steve Holland from 5th SFG(A) and Cris Murray from AMU stated that a 1/12 twist would be the best choice. However, there were NO such barrel blanks readily available in that time period--on the other hand, there were a whole bunch .270 barrels in 1/10 twist, so that while not ideal, 1/10 twist barrels were the field expedient option that was used for the early 6.8 mm testing. In addition, the original 6.8 mm 1/10 twist 5 groove Mike Rock barrels that Cris Murray chambered at AMU used a looser chamber, similar to the current SPCII or DMR chamber, NOT tight like the Remington SAAMI chamber.
So the bottom line on 6.8mm is simple: Just like making sure your AR15 has a true 5.56 mm chamber and proper barrel twist, it is also critical in 6.8 mm to use something like the original AMU/"Murray" type chamber, either the current SPCII or DMR, as well as the superior 3 or 5 groove 1/11 or 1/12 barrel twists--the Remington SAAMI spec chamber is too tight (like a .223 chamber) and the 1/10 6 groove barrels needlessly increase pressures and reduce velocity.
Hopefully that will provide the info you are looking for.
I heard a rumor Noveske is changing to the spec II and going with a 1 in 12 twist.
Word on the street is there's 1 or 2 more larger companies to follow along.
I like that info, as I still plan to do a 6.8-besides, it's on my paperwork as a listed caliber for my sbr:cool:
As always thanks Doc, I will look for those specs.
I just wanted to add a couple things about the chamber specs. DocGKR mentioned to make sure that the chamber is Spec II or DMR. As he stated, this is probably the most critical portion of achieving much better velocities with lower pressure. The twist also has pressure effects and is shown in the latest testing done at HTRs ranch in Texas. You can see and read all about the test in either the link I gave or the download that DocGKR gave.
As Doc said, the original specs developed by the two people most responsible for this great cartridge were ignored by Remington when they submitted their specs to SAAMI. The specs of the SAAMI chamber that they submitted are the exact same as the Spec II with the exception of the amount of leade!!!!!!!!! This is THE MOST CRITICAL ASPECT for achieving higher velocity at lower pressures.
As Constructor puts it in a thread over in 68forums.com about the leade measurements: "The length of the leade should be longer than Saami, the DMR or SPCII chambers take care of that problem. The problem with the SAAMI leade is that when you seat certain bullets to the max OAL of 2.28 as shown on the SAAMI drawings the ogive of the bullet is jammed into the lands and that raises pressure. Even factory Hornady 115grs are loaded to the cannelure and that allows the bullet to contact the lands. By making the leade longer it keeps the bullets away from the rifling."
SAAMI length of leade is .064"
Spec II length of leade is .105"
DMR length of leade is .095"
There are some more differences in the specs of the DMR chamber to the other two as this chamber was developed by Constructor to impart maximum accuracy without sacrificing pressure for those that wanted to wring out that nth degree for their rifles. One of the major differences is the angle of leade to lands. In the SAAMI and Spec II, that angle is 45* where in the DMR it is reduced to 30*. Like I stated earlier, this is the chamber for those that want custom barrel performance with their custom barrels. You can contact Constructor at his website for further information: http://www.ar15performance.com/. I believe he is building uppers now for those that want his performance out of their rifles.
One other thing about twist rate and I will let Constructor expound on this, "The twist rate has a big influence on pressure for some reason. I have never seen the twist rate make such a big difference in other calibers. I think, just my opinion the 11 twist is the best all around twist. It will allow everything from 85gr up to 130gr and even the 120 Barnes solid which is as long as most 150s. Hopefully we will find out soon if the 11 twist will stabilize the 105gr custom bullets for use in bolt action or by single feeding ARs, they have a BC of .505.
The 12 twist will stabilize everything upto 130gr Sierras and that again IMO is as heavy as you want to shoot in a 6.8 just because of powder capacity."
If more information is needed, please register over on 68forums. It is free and just like here, they are a great group of guys dedicated to helping others with this round. Here is the link...http://www.68forums.com/
The reason to register is because the owner Cold wanted to keep out the spammers and porn that get into so many other sites.
I hope this helps a little.
Kelly (Cohibra45)
There is so much data, and hearsay, around to wade through does anyone have chrony data on regular SSA loads from 10.5", 12.5" and 14.5" barrels?
Also, I do not see a separate listing for SSA "Combat" loads on their site. Is this something you have to contact Art directly to buy?
Thanks.
There is so much data, and hearsay, around to wade through does anyone have chrony data on regular SSA loads from 10.5", 12.5" and 14.5" barrels?
Also, I do not see a separate listing for SSA "Combat" loads on their site. Is this something you have to contact Art directly to buy?
Thanks.
Sorry Shivan, all the recent testing was done with 16" - 20" barrels. These tests were actually done to dispel any questions about pressure/velocities achieved using different chambers and twists. As with all tests, sometimes they bring on more questions than they answered (as with your questions, which are good BTW). There are several people on the 68forums that have SBRs but I'm not sure that they have access to chronys. Maybe Art at SSA can send you some data on their standard loads in the barrel lengths you ask for. I seem to remember that in some original tests, on different length barrels, velocities were given. But, I'm not sure if they were using SSA standard ammo or their own hand rolled ones... Art over on SSAs website has some velocities stats, but again, those are his 'Combat' loads out of a 16" barrel. http://www.ssarmory.com/ballisticsdata.aspx
Here are some stats from the original posting by Tim_W over on 68forums.com. http://www.68forums.com/viewtopic.php?f=1&t=839
"Velocity Differences of Bullet in Different Length Barrels
SSA 2nd generation 115 gr SMK OTM w/cannelure, 5 shot averages:
20” barrel: ave vel = 2561 fps; 10 fps extreme spread
16” barrel: ave vel = 2525 fps; 18 fps extreme spread -- lost 36 fps from 20"
12.5” barrel: ave vel = 2384 fps; 12 fps extreme spread -- lost 141 fps from 16"
10” barrel: ave vel = 2265 fps; 27 fps extreme spread -- lost 119 fps from 12.5"
7.5” barrel: ave vel = 2035 fps; 27 fps extreme spread -- lost 230 fps from 10"
--------------------------------------------------------------------------------------------------
20" barrels: Rifle Length Gas System.
18": Midlength Gas System.
16" barrels: Best with Midlength Gas System, but will also work with Carbine Length.
14.5" barrels and below: Carbine Length Gas System.
from PaulSantos"
I believe Paulo posts here and you might be able to PM him and ask him about the barrels he used to get these figures.
Maybe this will help a little??
When ordering from SSA, you specifically have to ask for 'Combat' loads. They will ask questions to make sure you have a rifle that won't have any problems when using their faster loads.
Kelly
That is helpful info, not sure how I missed it from Tim_W's posts, but I did. Thanks again.
Thanks guys this is very helpful. I will build my own and use the current specs.
Well I don't know about what the guys who are pushing the envelope with the 6.8 are doing to get close to those specs you're asking about, but there are some guys getting pretty close to those numbers with .243 loads. There are competitions shooters using bullets in say 107gr that are getting right close to 3000 fps with certain loads, you can read up on it at the 6mmbr site on the .243 page (http://www.6mmbr.com/243Win.html).
I've always wished there were more people looking seriously into the .243 and the AR platform.
I don't mind the 6.8 spc, but I think a necked down to .243 version of this round would be the perfect battle round. It would cover long range and short range with enough speed to get the job done. I don't think the 6.8 spc can take the place of the .308 and the .223 both. Its better than the .223 if you can get 2800 - 3000 fps out of the muzzle. But the .308 will always be a heavier and a more powerful round. I think that was the mistake in producing 6.5 and the 6.8, they wanted to replace both the .308 and the .223. They should have put there efforts in replacing the .223 and not worrying about the .308. If they would have done that, I believe we would have a 5.8, 6.0 or 6.2 spc instead of the 6.8.
Ned Christiansen
11-04-08, 09:45
I am not an expert on the 6.8 by any means, but, due to demand, I am going to be offering a shoulder-forward-only reamer in this caliber that is analogous to my .223-to-5.56 reamer ( http://m-guns.com/tools.php ). In short, it pilots into the bore and (more so) into the existing chamber in the front, and into your upper receiver bore in the back via a 1" band in the handle. The reamer does not cut, is not capable of cutting, the body or shoulder of the chamber. It only cuts the neck diameter and length, the freebore diameter and length, and the throat angle.
The first few will be ready in about two weeks, and one of them is spoken for. I'm starting out small here to see how many really sell-- I've had a lot of people tell me it's needed but that's not always the same as selling a bunch.
The first few will be ready in about two weeks, and one of them is spoken for. I'm starting out small here to see how many really sell-- I've had a lot of people tell me it's needed but that's not always the same as selling a bunch.
I'd get one, eventually... My 6.8 stuff is not yet taking off, waiting for a barrel from an unnamed source for a while now.
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