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Discussion Starter · #1 · (Edited)
So, now that most manufacturers (thank God) are producing the "SPCII" chambered rifles vs. the old, or bad, SPCI chambers, what official print are "they" using?

I know Harrison/ARP has several of his own versions, I'm more referring to the masses.

Can anyone post the official SPCII print?

From Daniel defense: "The Daniel Defense 18" 6.8mm SPCII S2W® barrel"

From Rock River: "6.8mm Rem SPC II chamber"

From LWRC: "
Our SIX8-A5 Uppers proprietary design has been optimized for the 6.8 SPC II cartridge."

From Stag: "this rifle uses the 6.8 SPC cartridge" - I don't see 6.8SPCII mentioned anywhere - may have missed it. I assume they're using the 6.8SPCII chamber though, no?

From White Oak:
Our White Oak 6.8 AR15 Rifle Barrel is Match Grade Stainless Steel with mid-length gas system and SPC II chamber for use with high pressure loads,

So, is there (1) core print all of these places are using called the 6.8SPCII? SAAMI of course only has the "original" 6.8mm Remington SPC listed...

A Google search for 6.8SPCII Reamer Print brings up a few variations... is this one the "official" one?
 

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Discussion Starter · #2 ·
Found this from Yama... explains a bit...

I have come to understand there are 3 elements that allow better pressure handling in an SPCII chamber than a SAAMI chamber.
Well really 3 things the guys did when they created SPCII.
First was to change the freebore/leade from .050 to .095 to .114 depending on if an ARP (.095), Noveske(.100) or SPCII (.114)

From the 6.8 Wiki, yea I know but its a good explanation
There are several different chambers for the 6.8 SPC which yield different results. They are:


  1. Original Murray 6.8×43 ERC developed in 2002.
  2. Murray DMR chamber, which was meant to address improved accuracy expectations for the ERC Special Purpose Rifle program in SOCOM.
  3. The Remington SAAMI submitted specifications. It was supposed to have a 1.3 mm (0.050 in) freebore, 45° cone angle, 7.1 mm (0.278 in) ⌀ freebore. The reamers and PTG prints had an 80° neck to freebore cone angle, which was a result of a mistake in the reamer drawing submitted, and was never corrected by the reamer maker or Remington during the process of tooling up for the testing protocols that eventually drove the SAAMI submission.
  4. SPC II is current standard chamber used by most barrel manufactures. It has been said to be very close to the original Enhanced Rifle Cartridge Program chamber. It has a 2.9 mm (0.114 in) freebore, 45° cone angle, 7.1 mm (0.278 in) ⌀ freebore, 7.84 mm (0.3085 in)neck.
  5. 6.8 ARP(6.8×43mm renamed )(DMR has been replaced by 6.8×43/6.8 ARP, both are/were created by AR Performance). It has a 2.4 mm (0.095 in) ⌀ freebore, 45° cone angle, 7.05 mm (0.2775 in) dia, and a 7.84 to 7.85 mm (0.3085 to 0.309 in) neck.[Proprietary chamber]
  6. Noveske Mod 1 designed by Noveske Rifleworks LLC. It has been said to have a 2.5 mm (0.100 in) Freebore.[Proprietary chamber]

Only the rifles chambered with the newer specified chamber (6.8mm Spec II, Noveske Mod 1 and 6.8 ARP chambers) can safely use the higher pressure military/tactical and near max-maximum handloaded ammunition. Those rifles using the Original SAAMI specs should only be used with the standard commercial cartridge pressure (Specified by SAAMI).
Second is the forcing cone angle which is described above

Third is the land to groove ratio.
If any of these SPCII style or .085+ (ARP Triad) freebore chamber still used the 50:50 land to groove ratio of the early 6.8 barrels they would still have pressure problems.
Its actually been said to me that a .050 freebore/leade with the correct forcing cone angle and a 70:30 groove to land ratio or better would still have good pressure handling and perhaps be more accurate.

So there are 3 elements to the newer barrels we have today.
YMMV
 

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The reamer print you posted needs to be destroyed. It is PTG's SPCII reamer that still has the bad cone angle. It doesn't matter what angle is written in the box it's all in the dimensions. The distance between the end of the neck and the start of freebore needs to be at least 0.015", not 0.005".

With a neck dia. of 0.308" there should be 0.020" difference.
 

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Agreed on the explanation quoted. The land/groove ratio was one of the major points of contention which would NOT be recognized/acknowledged when one certain knucklehead was on his marketing mission for his pet caliber. He kept wanting to insist that SAAMI was good enough for the 6.8 and that his data for the 6.8 was all that mattered. (Because it made his pet look better). The better rifling of barrels offered by the core group of sponsoring vendors, and the continued efforts of enthusiasts to "edjumicate" the more mainstream brands to dump the use of SAAMI chambers and 6-groove Enfield .270 barrels appears to be coming of age.

The "more gooder" chamber/rifling available from our sponsoring vendors are what make the difference in the performance, and WHY new folks are always directed towards making their purchases from sponsoring vendors of the forum. It's not JUST because of being fanbois, or because they help keep the lights on. They're offering a better performing product (because of the more favorable specs which perform better). And, when a larger name brand of barrel sees the light and produces product more in line with what the 68 community KNOWS to be better... they receive a warm welcome.

On the other end, Ruger's top man invited "input". His response to the input received concerning his company's use of SAAMI specs... they stopped offering a 6.8 altogether. Ruger's driven by the legal dept., and they like the comfort of SAAMI. It's a shame too... because Ruger could've done well with a better spec'd offering, and could clean up with an SPC II submission to SAAMI.
 

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Discussion Starter · #5 ·
The reamer print you posted needs to be destroyed. It is PTG's SPCII reamer that still has the bad cone angle. It doesn't matter what angle is written in the box it's all in the dimensions. The distance between the end of the neck and the start of freebore needs to be at least 0.015", not 0.005".

With a neck dia. of 0.308" there should be 0.020" difference.
Ok I pulled the photo so no one confuses it for the "official" print or standard.

What's the standard one companies use?
 

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Somewhere, there are threads with drawings posted. I believe Carnaby has posted the one he uses in at least one of the threads.
 

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Ok I pulled the photo so no one confuses it for the "official" print or standard.

What's the standard one companies use?
According to a post from H a few years ago they were using a version of the print you posted as PTG wouldn't correct the numbers.

That print is one of the first ones that comes up on a google search and I cringe every time I see it. I'm sure if you corrected the numbers for the leade it would be a good safe chamber.

http://68forums.com/forums/showthread.php?13067-6-8-SPC-II-reamer-and-DMR-reamer
 

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I think the one you had up with all the highlighted areas is correct. I traded 5 or 6 emails with PTG in 08 because they kept changing my print to their 1.701 number. I tried to tell them they had transposed it and it need to be corrected. After 5 emails I gave up trying to convince them they had made a mistake, I said leave my print alone and grind it to the numbers I have on my print. Ben with Bison finally convinced PTG that they had transposed the numbers and they corrected it in early 2010 I think. I thought it was 09 but according to that thread it looks like 2010.
 

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Discussion Starter · #9 ·
I think the one you had up with all the highlighted areas is correct. I traded 5 or 6 emails with PTG in 08 because they kept changing my print to their 1.701 number. I tried to tell them they had transposed it and it need to be corrected. After 5 emails I gave up trying to convince them they had made a mistake, I said leave my print alone and grind it to the numbers I have on my print. Ben with Bison finally convinced PTG that they had transposed the numbers and they corrected it in early 2010 I think. I thought it was 09 but according to that thread it looks like 2010.
Are you referring to this one as being the "correct" or, "real", or "now commonly used" 6.8SPCII Print?

 

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Are you referring to this one as being the "correct" or, "real", or "now commonly used" 6.8SPCII Print?

Yes That date in the upper right was the date the first 6.8 print was drawn by PTG not the date of the revision. The 1.7113 is the critical number to establish the cone angle.
 
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