What did they do to their brass?
What did they do to their brass?
But you haven't ever tested any 6.8 have you? You relate that to 6.8 bullets that are over size which none are as a matter of fact most are .2765 and not even .277. We also know and have proven the chambers and rifling designs do make a huge differance in performance. One more thing if a reamer has a throat dia of .277 how big of a hole does it make?
Last edited by constructor; 01-24-12 at 23:17.
I know the results of two tests - one by Western Powders ballistics lab, and the other by a SAAMI-member company. Both were done with professional instrumentation. A test barrel was made with a SAAMI chamber and tested for pressure with calibrated reference ammo - 55,000 psi. The chamber was then throated to SPC-II, and the pressure was re-tested with the same ammo. Pressure dropped by 1500 psi. New ammo was created with more powder to restore pressure back to 55,000 psi. The result - this new ammo in the SPC-II chamber was about 30 fps faster. I once posted the original emails from Western.
The only reason why people think SPC-II ammo is so much faster is because the companies loading it are loading it over-pressure. If SPC-II became a SAAMI standard, it would not be loaded over pressure, and people would be disappointed to learn it was only 30 fps faster - and then wonder what all the fuss was about for the last 8 years.
Last edited by rsilvers; 01-25-12 at 08:46.
So a M1S barrel that blows primers at 2450fps is only 30fps slower than a high performance barrel that can shoot the same bullets at 2800fps??? That is why we changed the barrel specs, to get the BEST performance from the barrels. The SAAMI barrels made in 2006 were blowing primers with the best hanloads at 2450fps. Now we have barrels that will push 110gr projectiles to 2800fps without blowing primers. Are they high pressure? yes but I guess they were high pressure if they were blowing primers out of the SAAMI barrel too. Dang, thats about 500fps faster than the 300BLK isn't it?
The chamber is not the only component which effects pressures. It is very important to not have the bore cross-section area go below the SAAMI minimum of 0.0596 square inches.
Regarding the Model-1 sales barrels - section one and put it on an optical comparator. Note the bore area before drawing conclusions about the throat dimensions being the main contributor to pressure.
As for your comparison to 300 BLK - meaningless. I can make a barrel that will shoot hot hand-loads also.
No kidding. At least it is a small step in the right direction. When I was fighting with them to do something about my 77-22 that shot 6-8 inches at 50 yards the best I could get was "it meets Ruger accuracy specifications." "What are those specifications?" one might ask. They are a trade secret. I don't much care what Ruger does. I've got about all the big revolvers I want and outside of the LCR they don't make much of anything that interests me. The General Motors of the gun world.
I give them plenty of credit for being prolific. They have always preferred quantity to quality.
Wow. And again, I say...wow.
Last edited by Suwannee Tim; 01-25-12 at 12:09.
I thought you said the 8 twist didn't make any difference in pressure so your 8 twist barrels should be able to shoot hot handloads huh?
But the guy that used a 300 in the 3 gun comp used a 12 twist hmmm wonder why?
You will never get a 16" 300BLK to shoot 110gr bullets at 2800fps while not showing signs of high pressure.
Didn't you say the 6.8x43 should show more pressure than a SAAMI chamber? Isn't that about throat dimensions, length and dia? Do you still think a reamer that is .277 dia will cut a .277 dia hole? So does that report you read mean that the tested throat diameter of the barrels were actually .308 and .309? ...and the reamers used to cut those throats were...?
Getting confused between chamber dimensions and reamer dimensions?
So what do you really know about the SAAMI and 6.8x43 chambers?
If the bullet does not touch the sides of the throat and the bullet is fully engaged in the rifling before the base of the bullet leaves the case mouth allowing gases to leave the case still being trapped behind the bullet because the body of the bullet completely seals the bore how does the throat dia (a .0005 difference)make any difference in pressure?
Now about freebore length. If the bullet can move forward an extra .050" before meeting the resistance of the lands that is similar to loading to a longer OAL making more case capacity and less pressure similar to Weatherbys rifles with a .250 freebore. He seemed to have good results getting more velocity with his rifles, about 200fps as I recall.
Yeah I think I knew that bore area issue about 6 years before you tried to draw a 308 button with a diameter larger than .308. Lucky for you the button maker caught your mistake. Our goal was to make the 6.8 perform as well as it possibly can and we did. The chamber and rifling configuration makes less pressure, more velocity and is more accurate.
Some times you have to think like a machinist to get the desired results out of machined parts rather than thinking like an inganear who believes everything can be figured out on paper. There is no substitute for hands on experience.
As for Ruger and their 6.8, for whatever reason the mini isn't accurate if they want to sell them they need to fix it. Their piston 6.8 was expensive and a piston. Most of the 6.8 market is hunters, they just want to hunt and not spend extra money to do it. Ruger makes other fine products they just missed the mark this time.
Last edited by constructor; 01-25-12 at 12:23.
Gentlemen,
Lets keep the underhanded digs and personal or perceived personal attacks out of tech. If you can't do that, Staff will be happy to come in here and clean house. This site, unlike other large AR15 sites, won't stand for anything less than professional conduct. By posting on this site your agreeing to the code of conduct, so review it if you need to, otherwise its assumed you are complying with it when posting.
Act right and act accordingly.
John Noveske Changed My Life.
1.4.13
Twist plays almost no role in pressure. This is why SAAMI only suggests twists, but does not have a maximum twist rate. When the M16 went from the 1:14 to 1:12 to 1:7 - some predicted pressure problems because M193 ammo was already hot on pressure. Those concerns turned out to be unfounded. Likewise, 308 has been compared with 1:12 to 1:8 and there were no pressure/velocity differences. 6.8 does not have special rules.
You mean this: http://bulletin.accurateshooter.com/...gun-nationals/
They got good results with the selection blanks they had in stock for their 30 AS.
No doubt that 6.8 can reach higher velocities than 300 BLK. That is one of its advantages over 300 BLK.
Reducing the throat diameter to the minimum dimensions on the 6.8x43 DMR chamber would be expected to raise pressures more than the short-throat does on the SAAMI chamber.
No, I don't think a 0.277 reamer will cut a 0.2770 hole, but I was always speaking about chamber dimensions, not reamer dimensions.
This is the report:
http://www.border-barrels.com/articl...Consortium.htm
It shows that tighter throats raise pressure, regardless of bullet size.
See this article:
http://www.border-barrels.com/articl...Consortium.htm
Specifically the charts like this:
Notice how with 30 caliber bullets there is a 600 BAR (8700 psi) spread between a 0.310 and a 0.307 throat. So each 0.001 smaller in throat diameter, the pressure went up about 2200 psi. Note that this does not require the bullet to be larger than the throat to be true.
Another problem with tight freebores, especially for semi-autos - is that the bullets that are not perfectly concentric in the brass case will rub on the way in and increase the chance of failure to chamber.
Yes, the SPC-II and 6.8x43 chambers have that feature and it does reduce pressure - about 1000 psi typically (1500 max).
From Art at SSA:From: Robert Silvers
Sent: Thursday, July 14, 2011 5:06 PM
To: Johan Loubser
Subject: Re: Western Powders Ballistic lab
Johan,
Have you ever done a test where you take a 6.8 SPC SAAMI test barrel, measure velocity and pressure, then ream the same barrel to 6.8 SPC-II - and add more powder to match the pressure of the previous test, and then see how much extra velocity there is?
Robert.
----------------------------------
Robert,
Yes we did exactly that and the difference was negligible as to be ignored ca 20-30Fps and <1000Psi.
I know there is a lot of claims out there regarding this.
Some apply the effects of other calibers (such as the 223Rem) with completely different expansion ratios to the 6.8SPC.
The 6.98Spc is not sensitive to the slight changes in dimensions between the std and SPEC II.
Regards
Johan Loubser
Ballistician
Ramshot.Accurate.Powders
The 0.001 smaller freebore of the 6.8x43 DMR would be expected to raise pressures about 2200 psi - so one could expect it to come out at about 600-1200 psi more pressure than a SAMMI chamber. The 6.8x43 chamber I would expect to come out about -100 to 400 psi ahead of the SAAMI chamber, and about 1100 psi behind the 6.8 SPC-II chamber.I can not disagree with Bob's statement of only 1000 -1500 PSI reduction and <30 FPS increase with a given load and projectile with respect to the SAAMI VS the Spec II chamber
308 grooves are 0.3080 +0.0020 -0.0000. So the groove diameter can be anywhere from 0.3080 to 0.3100 and be in spec.
I have never tried to make a 308 groove diameter that was oversized.
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