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Discussion Starter · #1 ·
I will not comment on Noveskes or Bisons chamber since I have never seen a print of either.

I think most know the history of the 6.8 and the problems along the way but for those who do not.
The original Remington 6.8x43 SPC chamber was approved by SAAMI with a .050" long freebore. Murray, Lawton and Holland say they believe the wrong print was sent to SAAMI or SAAMI changed the freebore length. Either way things went sideways and primers were being blown everywhere and that was mistake #1.
Jan of 2006 I was testing my first barrel, purchased online and the Hornady Vmax ammo I was shooting was blowing primers. I looked online and discovered SSA, called Art and talked to him and he laid out the whole thing. He told me of another company and I purchased one of their barrels chambered in 6.8 SPCII, a SS Fluted barrel that cost close to $600. I started testing that one and things were good for a short while. I was cleaning it and when I withdrew the rod and brush a ring was hanging on the brush. Turns out it was a copper ring. I called Art back and talked to him about it and started researching the 6.8, everything I could find. During that period I found that the SAAMI spec showed the maximum cartridge size could be larger than the minimum chamber size. Art told me PTG was making most of the reamers so I asked PTG to send a reamer print. It turns out someone who re-drew or designed the SPCII reamers transposed a number which caused a 80* cone angle in the chamber and that sharp edge was shaving copper slivers off the bullets, that was mistake #2. There is a huge thread on arfcom in the archives that explain that whole deal with Art and Randall going back and forth for months.
Start of the ARP chambers-I took that drawing that PTG had sent me and changed the number that had been transposed to make a 30* cone angle thinking less of an angle would shave less copper from the bullets but changing the cone angle would also make the jump to the lands longer so I shortened the freebore length to try to keep the length at which the bullets touched the lands the same since I could not get near touching the lands at mag length in a PRI mag.
When the reamer came in I reamed the WOA barrel with the new reamer and started testing again, huge difference. That was the DMR chamber. When Tim W and I started making production barrels we drew a reamer .001" larger in diameter to make the difference up that the chromelining would make. That was intended to be the DMR-C chamber, "C" for chrome. Later after some problems I found both of those carbide reamers were ground by PTG to the very minimum spec and they were tight with some ammo, that was mistake#3. That was probably late 2008 early 2009. Somewhere around the same time SSA decided to make the necks of the ammo thicker to keep them from splitting. The necks loaded with bullets that were .277" in diameter were .309" or larger than the neck in the chambers and larger than the SAAMI spec. The loaded ammo was sticking in the necks, mistake or problem#4. And we dropped the chrome lining after 3 batches.
So somewhere after July 2009 I changed the drawing again to make sure the body diameter to include the neck was not a +- tolerance but only a +. The designed freebore length as far as where the bullets touch the lands(end game) remained the same as it always was, but I changed the cone angle to 45*. The actual reamer sizes as opposed to designed sizes still went up and down and that continued to be an issue until I changed to using JGS to grind the reamers.
Somewhere in that 2009-2012 Hornady began loading the 120SST. The SST ammo had and still has a bulge apx 1/2" from the bottom of the case. When I started using JGS I added a new dimension point to size the diameter of the base straight from the top of the groove to 1/2" to take care of the bulge everything else remained the same. All of these changes were small.001-.002" changes. I've lost count of how many problems there has been but the cartridge has been flawed from the first day SAAMI approved the specs
 

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Thanks for the info.
A couple of weeks ago I ran some calculations and realized that I had posted incorrect information a couple of times in discussions of the original SAAMI chamber dimensions. Sorry about that. I had been under the impression that the SAAMI drawings had the wrong dimensions for the cone between the case neck and freebore. The SAAMI dimensions are correct for a 45° angle. As Constructor stated, the problem was with the PTG reamer which had some numbers transposed. Here is a drawing showing which numbers were transposed. As noted on the drawing, the biggest problem was with the X-Treme bullets, which had a copper plating over a relatively soft lead core. The thinking at the time was that the bullets obturated enough upon firing that the sharp angle at the entrance to the freebore would shave rings of copper. Sometimes the rings would build up enough after a few shots that subsequent rounds would not chamber.
Rectangle Schematic Font Slope Parallel
 

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Discussion Starter · #3 · (Edited by Moderator)
A few things to note about that drawing, first in the center bottom box it says "tolerances' +-.001". If PTG grinds that reamer to the minimum making the base at the chamber .421" Hornady 120gr SST ammo will stick in the chamber. The necks will be .307" and the freebore will be .2771" All of those dimensions can cause issues with certain ammo.

ETA- In addition the size dies are tied into those problems. Big long argument years ago. Small base dies resize the brass .002" smaller in diameter than FL size dies that is all, the user is responsible to adjust the dies up and down for the shoulder set back. I called every die manufacturer and asked what their design diameters were. Redding would not answer. Hornady said all of their dies size the brass .004" under the minimum chamber diameter size making them small base dies. RCBS and Forster said their FL dies size the brass on all cartridges .002" under minimum chamber size and their SB dies size the brass .004" under the minimum chamber size. Taking into consideration size dies also have tolerances.
So some of the old timers here will remember the arguments between EWP and I, we went round and round about this. IF PTG grinds a reamer to the minimum size and people use FL dies that are made to their maximum diameter brass can stick in the chamber. I had that issue with the Redding dies. Tim W found a set that would push the shoulder back .020" shorter than SAAMI spec if the dies were screwed down to the shell holder as the instructions said. If people followed the instructions they would have blown primers since nothing was behind them holding them in the case.
If you haven't heard this before DON"T JUST SCREW THE DIES DOWN TO THE SHELL HOLDER.
 

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I was waiting for H to add in those last couple of posts from the other thread before closing this one. Here's the deal. The reason I'm not going to leave this thread open for every tom/dick/harry to slap their opinions into the fray is, I don't want this thread to be just another place to gather opinions and arguments. If something is to be submitted here, draft something for submission to a Moderator, as we get time, we'll open the thread for that person to add their submission to it, or not. The door to this thread will be kept locked for those reasons.
 
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