It did not take this long to write the bible

Originally Posted By coldair: It did not take this long to write the bible

YUK, YUK, YUK,

Ok, OK, give us a break.  It has only been two weeks, and I predicted it would take about that to write this up.

When you see the depth and scope of this report, then you will understand how we could get it out in two weeks, only by working on it day and night.  I know Tim W spent 40- 50 hours on it.  This took a lot of passion and dedication...we're not getting paid for this.

It was 50, yes FIVE -O pages before Tim W, Harrison and I sat down together to proofread, edit and apply Occam's razor.

HTR/Tim_W/Constructor, please don't pay too much mind to folks' bitching and moaning about the time of release; I am quite confident that once they see y'all's thoroughness, they will soon forget about the temporal aspects.  Y'all have invested a substantial amount of effort into this program, and the only proper way to present the data is right the first time.....that takes an awful lot of very hard work!  

The anticipation is certainly understandable, but Rome wasn't built in a day.

Originally Posted By Cold: It appears that a preliminary is posted on 68forums.com here 68forums.com/viewtopic.php?f=1&t=3473

Where do I paypal to the beer fund?

Looks like a job well done, but I don't want to speak too soon. Let me chew on this for awhile!

Guys,

I really appreciate your patiences. The testing and report ended up being quite a undertaking. I hope it doesn't disappoint. These things really do take more time then is readily apparent. There is certainly a learning curve to these things. While we always would like to have more data and more uppers and various spec barrels etc.I think we did well for what we had. I have to thank Constructor and HTR for a few long nights helping put the finishing touches, proof reading etc.. Not counting the actual testing the work put in for the report reached close to 85-90 hrs or me alone.  I will just say that sometime things that would be thought to take little time eat it up a considerable amount.

The report is in JPG format so that it can be read online without having to download it and have only a link in the post. There is a link at the bottom where the report can be down loaded in its entirety. This first report is only the spread sheet summary of the test.The following report will be the entire report. The link at the bottom of each will be to download the article that is above it. The Summary will have a link to the summary like wise for the entire report. We did our best to record as many data points as was possible in the short time we had for the actual test. I tried to include as much pertinent data as possible in the report without it being full of filler.

Again I nor HTR or Constructor are seasoned ballisticians sp? but I feel this does represents a good amount of data that we gathered in such a limited amount of time.  I hope the data in the report will prove useful.  Thanks again for your patience and  I apologize to those that waited up last night to no avail as I didn't get it posted till very early in the AM today on 68forums. I think around 12:30AM

Here you go:



Summary Data Chart Only












Link to download: 6.8 Performance Data Summary Report PDF
                                 Full Performance Report




































































































Link to download: 6.8 SPC Performance Testing Report PDF Full Report


Thank you to all those who helped in anyway with making this test happen.

TimW

Very well done indeed! It can’t be overstated how commendable it is for people who are so passionate about something to engage themselves in something like this… and for no personal return. This is a great benefit to the advance of the cartridge as well as a primer in general internal ballistics. The safety message that can be garnered from it is invaluable in and of itself. All in all, there is a lot of very good information to chew on there. I applaud you all!

I, like many others, will undoubtedly have to take some time to chew on it, digest it a bit, and eventually comment on it. Where’s the Tabasco sauce…

Me too.  That is why I went to such  extremes to attempt to rough up the surface.  But even a few minutes under a high speed cutting wheel did nothing but round down the wheel.  I guess you could call that a test of sorts which it pasted IMHO

About the bore gauge, we only had the one.  Ideally we would have liked to have had that one to be .269 as you only need .001 to allow it to drop thru a .270+ bore.  Having a larger gauge would have been interesting as well.  We had actually discussed it but all we had on hand was the one gauge.  Something like .2705 and then .271

One thing is for sure even without the pressure equip hooked to your barrels there it was very evident the diff between the pressure of the SAAMI vs SPCII.  There was such a huge dif in the cases when you looked at what the PSI was from other barrels that had the same looking cases I would estimate a 4K min difference. If another test was ever done with your barrels we will have to have one that has had a specific spot left uncoated.  Also the only way to really measure the effect of the coating on performance/pressure would be to have two twin barrels with one uncoated.

As far as bore size goes the ideal would actually be to have a slight taper from breech to muzzle. Example for a 20": start at .271 and end with .270 would give you more vel with an actual drop in peak chamber PSI with an increase in vel with no loss of accuracy. Custom barrel makers years ago use to put a slight taper on bore when they hand lapped them.It was more of an art which is all but lost now. What it does is extends the actual pressure curve so there is more area under the curve.

Originally Posted By Tim_W: Me too.  That is why I went to such  extremes to attempt to rough up the surface.  But even a few minutes under a high speed cutting wheel did nothing but round down the wheel.  I guess you could call that a test of sorts which it pasted IMHO About the bore gauge, we only had the one.  Ideally we would have liked to have had that one to be .269 as you only need .001 to allow it to drop thru a .270+ bore.  Having a larger gauge would have been interesting as well.  We had actually discussed it but all we had on hand was the one gauge.  Something like .2705 and then .271 One thing is for sure even without the pressure equip hooked to your barrels there it was very evident the diff between the pressure of the SAAMI vs SPCII.  There was such a huge dif in the cases when you looked at what the PSI was from other barrels that had the same looking cases I would estimate a 4K min difference. If another test was ever done with your barrels we will have to have one that has had a specific spot left uncoated.  Also the only way to really measure the effect of the coating on performance/pressure would be to have two twin barrels with one uncoated. As far as bore size goes the ideal would actually be to have a slight taper from breech to muzzle. Example for a 20": start at .271 and end with .270 would give you more vel with an actual drop in peak chamber PSI with an increase in vel with no loss of accuracy. Custom barrel makers years ago use to put a slight taper on bore when they hand lapped them.It was more of an art which is all but lost now. What it does is extends the actual pressure curve so there is more area under the curve.

TimW,

I believe you are talking about the magical/mystical 'Perfect' barrel!!!

Great work you guys did!!!  

Thanks to you, Constructor, and HTR

Update:

If I don't get bitch-slapped by Hurricane Ike, I am getting ready to load some of the GS 80 grain bullets (that Tim so graciously gave me), using RE7.  I am guessing that it will perform best at charges of 28.5 through 29.5  grains.  The Speer TNT with 29.5 grains is super-accurate.  I am looking for right at 3000 FPS from my 16" barrel.  If you extrapolate from the pressure test, that load should be producing just about 55,000 PSI.

When my 12 twist, 3 groove is ready, I believe it will be up around 3150, just about equal to my 6mm Remington.  Now we're talking.

RE7 is a good powder for lighter, "varmint weight bullets," and I think it will likely give pretty good consistency and accuracy.  It is time to see if we can shoot little, tiny 1/2" groups with the GS, then on to testing them at 300, 400 and 500 yards for accuracy, actually using a scope

Actually HTR you need to add a grain and make that your starting load and load them at 2.30.  When I loaded norma 200 load that maxed out with the TNT I went 2 grains over that and I was still 100 FPS slower then what we got with the faster denser 1680. To put it in perspective GS recommends that you make your starting loads what the manuals give as a max loads for bullets of that weight.   You are talking about using the max load for a bullet that is 10 grains heavier.  norma and Rel 7 seem to fit about the same amount into the case within a grain. I had the case full almost flowing out of the neck.  IMO start @ 31 gr of Rel 7.  I still think you will be around 3100+. Its jsut that 1680 has so much more energy in it and the balls are the smallest I have ever seen.

Also don't forget how hot it was those days.

Originally Posted By Tim_W: Actually HTR you need to add a grain and make that your starting load and load them at 2.30.  When I loaded norma 200 load that maxed out with the TNT I went 2 grains over that and I was still 100 FPS slower then what we got with the faster denser 1680. To put it in perspective GS recommends that you make your starting loads what the manuals give as a max loads for bullets of that weight.   You are talking about using the max load for a bullet that is 10 grains heavier.  norma and Rel 7 seem to fit about the same amount into the case within a grain. I had the case full almost flowing out of the neck.  IMO start @ 31 gr of Rel 7.  I still think you will be around 3100+. Its jsut that 1680 has so much more energy in it and the balls are the smallest I have ever seen. Also don't forget how hot it was those days.

Thanks for the help, Tim.  I don't know what I would do without the advice of you and Harrison .  Actually, I ordered AA1680 from my local class III guy, and I just found out today that is has come in.  At your suggestion, of course.

Now, I will get to try the 1680, but rather than just duplicate the load you did, I wanted to try some of my own, with different powders.  You just never know how a bullet is going to react, until you shoot it in a particular barrel, right?

Originally Posted By AtlantaFireman: I see that you used H322.  This is a good powder.  You may wish to try Benchmark as well since it is another Hodgdon Extreme powder.  HE powders give less pressure variations due to temperature range. Texas is hot this time of year.

I agree, but it looks like Ike is going to cool things down a little...

Originally Posted By AtlantaFireman: Originally Posted By hi-tech-rancher: Originally Posted By AtlantaFireman: I see that you used H322.  This is a good powder.  You may wish to try Benchmark as well since it is another Hodgdon Extreme powder.  HE powders give less pressure variations due to temperature range. Texas is hot this time of year.   I agree, but it looks like Ike is going to cool things down a little... You are here. www.nhc.noaa.gov/storm_graphics/AT09/refresh/AL0908W5+gif/151313W_sm.gif

Though this is a tech forum (I apologize, mods) I need to state something here, because this is where my ARFcom friends lurk.  I wish to thank all you guys that sent me PM's about the Hurricane with wishes of "staying safe."  I even had a couple of you offer to allow me to stay with you.  I am amazed sometimes at the Internet with all its "inherent evils,"  at just how many really good people are out there.  Some of you don't even know me, yet you offered to help....and indeed this is a disaster.  This little forum binds us together....which is what is so cool about America.  I hope it stays that way.....

Everything is fine, here.  I have a little high water lapping at the back of my lot on the Bay, but it never got into the yard.  However, my parents / immediate family in Houston are literally being pounded by the southern end of the eyewall right now.. ...they have no power and their phone is out, too.  

If you are religious, please say a prayer for them...if not, then I sincerely thank you for the well wishes....

Yep all my family in League City / Kehma, about half way between Galveston and Houston, got pounded but all were safe. A couple lost their roofs and no water or power expected for the next 2 weeks but thats about it. Main thing is they were safe. Glad you came out OK HTR as you are only what 2' above sea level with the  back door 50 yards from the water.

Originally Posted By Tim_W: Yep all my family in League City / Kehma, about half way between Galveston and Houston, got pounded but all were safe. A couple lost their roofs and no water or power expected for the next 2 weeks but thats about it. Main thing is they were safe. Glad you came out OK HTR as you are only what 2' above sea level with the  back door 50 yards from the water.

Well, first off, everyone in my family is safe, and their houses sustained no damage, but they are now refugeed here with me... I have a house full of 10 people. I am actually enjoying the company.

As for my house, I am 9.25 feet above sea level.  Our lots here, sit on a little bluff, so we are pretty safe, and not on the barrier island.

One more photo:

Originally Posted By Tim_W: Me too.  That is why I went to such  extremes to attempt to rough up the surface.  But even a few minutes under a high speed cutting wheel did nothing but round down the wheel.  I guess you could call that a test of sorts which it pasted IMHO About the bore gauge, we only had the one.  Ideally we would have liked to have had that one to be .269 as you only need .001 to allow it to drop thru a .270+ bore.  Having a larger gauge would have been interesting as well.  We had actually discussed it but all we had on hand was the one gauge.  Something like .2705 and then .271 One thing is for sure even without the pressure equip hooked to your barrels there it was very evident the diff between the pressure of the SAAMI vs SPCII.  There was such a huge dif in the cases when you looked at what the PSI was from other barrels that had the same looking cases I would estimate a 4K min difference. If another test was ever done with your barrels we will have to have one that has had a specific spot left uncoated.  Also the only way to really measure the effect of the coating on performance/pressure would be to have two twin barrels with one uncoated. As far as bore size goes the ideal would actually be to have a slight taper from breech to muzzle. Example for a 20": start at .271 and end with .270 would give you more vel with an actual drop in peak chamber PSI with an increase in vel with no loss of accuracy. Custom barrel makers years ago use to put a slight taper on bore when they hand lapped them.It was more of an art which is all but lost now. What it does is extends the actual pressure curve so there is more area under the curve.

You didn't need gages at all. A few pure lead round balls, some grease, and the means to drive them through the bore would have provided much more accurate readings---though barrels with an odd number of grooves would require a special V anvil micrometer or some calculations to arrive at the proper number. This is a very old practice and it's still used by quite a few folks today.

A few years ago, I could have told you where to purchase a gage pin set for hole size XXX. The pins(at least on the sets I remember using/seeing) came in .0001" increments and IIRC, went from a half thou below nominal to a half thou above nominal.

Damn, I just ordered 5 6.8 mags, thinking all I really needed was a good bbl and bolt and some ammo. After reading this post, and seeing some of the Rifle Load Data on that forum, which shocked me with low velocities, I'm thinking I should have just got
308 mags instead. Now, we have the big twist debate, chamber debate, ejector mark problems, all when I thought the 6.8 had been out long enough for all of this to have been ironed out. I have an M1A if I need it, and a PSS as well. Just wanted something in an AR package with more umphh. Sounds like more of a headache. I do hope the fine people working to correct this are successfull and no one will unwittingly buy and get stuck with something that is problematic. I hope there will be a new Tacky soon on who to avoid, what works right out of the box, what the best ammo to have or reload is, etc....
Just skipping it all between 5.56 straight to .308 is a bit easier, like going from a small block chevy straight to a big block in my hot rodding days if you wanted simple, drasticly improved performance without spending as much time and money to do it.

Truely, good luck with all of this. Wish the Cprod AK mags were GTG. Got plenty of that ammo around.

.308 is heavy and requires its own lower rcvr...  

if you have a 5.56 already, all you need is an upper and 6.8 mags....  you can also use the .458 socom on that 5.56 lower with 5.56 mags dated....  

there really is no headache involved in the 6.8 ... just get an upper from the right people who know what the round is about....  the same guys who put together the report are coming out with a line of 6.8 uppers in jan 09  and the price on the base upper may be less than a cmmg but with far more detailed work and better barrel specs....   just stick with it and you will be rewarded    

WOW!  This thread is incredible.  I'm looking at diving into the 6.8 realm, and you guys are a wealth of information.  

I looked around at all of the sites I could find, and didn't see what I was looking for.  Does anybody make a light(er)weight 18" 1-11" twist barrel?  I've seen plenty of 18" SPR / DM barrels, and a few 16" lightweight barrels, but not exactly what I was looking for.

Thanks.

Here's an option:

1) Buy one of the last remaining Cardinal Armory 18" SPR profile barrels, and have it turned down by Harrison at AR Performance or by ADCO.  That is a simple and inexpensive operation.  Maybe turn it down the .720 under the guards and .650 out to the muzzle.

Then you would have a SPCII, 11 twist, 4 groove lightweight 18".  Actually sounds like a pretty good idea.

HTH

That sounds like a great idea.  Thanks.

I see Denny's also has an 18" SPR barrel.  How does the Cardinal Armory compare to it?  Is the barrel from Denny's worth the additional cost?  I see its nearly twice the price––although it does come with a bolt and gas tube.

they are both 11 twist, and I believe that Denny finally adopted the SPCII chamber.  You definitely cannot go wrong with the Denny's / WOA barrel either, but I don't know if he would turn it down for you.  The light weight is a great advantage, especially if you hunt on foot.

Wow.  After looking at the ballistics chart, it seems that the 6.8 isn't affected by barrel length as much as some other rounds.  It seems like only a 40 to 60 fps difference between a 16" and an 18" barrel, depending on bullet weight.  I expected a bigger difference.

I just ordered an 18" from Carndinal.  Too bad that they are going out of business.  I will have to go check out Denny's for a 16".

Yep and its even better when you go to shorter barrels especially if you hand load and can us faster powders.  We have a 8" barrel that is getting over 2300 FPS from the 115 gr bullets.  Then 12.5 are getting 2425 from the 115s not bad when you consider 16 are getting 2550-2650 depending on the rifling specs.  

Here is the way I see it working out using the best powder for each barrel length staying under 58K PSI:

8": 2300
10.5": 2375
12.5": 2425
14": 2500
16": 2600
18": 2665
20": 2720

Anything new on the 6.8 front? 68forums are down & I'm going thu withdraws!

I wonder why this isnt stickied?


I just want Tim and Harrison to get parts so I can get my Xtreme for my piggie hunt.... If I have to I will use QD mounts and use my 18 for both day and night hunting but I would rather set the 16 inch upper up with the aimpoint and PVS 14 and leave the scope on my 18 alone.

Don't worry:

If you don't have it by then, you can shoot my 16" CA with the Eo and the PVS-14 if you want to.  It is dialed in with the TTSX's to around 0.6" at 100 yards.

this report was tacked for at least a year.  I guess they thought it was time to let it roll to the "regular menu...."  

I just bought a new Cardinal 6.8 18" SPR barrel from a fellow ARFCOMmer. I should receive it in a couple of weeks. I still need to order a low profile gas block for it but don't know the barrel diameter at the gas port. Can someone who knows please tell me that diameter?

Brazos Jack

I appreciate it, and I am not worried about finding a gun to use I just really want to play with my new upper while I am home. If I dont get it then I will have to wait till july. :D

Either way should be fun in Feb.