12-01-2020, 04:14 AM
There were at least 3 different types of 6.8x43 chambers when Chris Murray was working on it at the AMU on his own time, before Remington took it to SAAMI.
One chamber would be more ideal for accuracy looking to fulfill the DMR/SPR solicitation that SOCOM was looking for. (That award ended up being the .223 Wylde SPR shooting 77gr SMKs from 5.56 cartridges, not anything 6.8x43). The 6.8x43 DMR chamber actually had a tighter freebore than projectile diameters, but it sure was accurate!
Another chamber was meant to allow more velocity since the SEALs wanted the 115gr going 2900fps, but nobody could safely reach those velocities of course, even after promising the SEALs that it was no problem". Several tried and blew up a lot of guns in the process at some very well-known companies.
Then there was another chamber that was supposed to be a balance between the 2.
SSA loaded at least 3 different pressure levels, 2 of which exceeded what the action will handle in volume, and this was demonstrated across a fleet of rifles with predictable results, all resulting in failure of critical pressure-containment components.
Ive heard a more detailed account of what happened with the SAAMI submission. I'll just say that no reamer maker worth their salt would purposely make a reamer with an unsafe hand-off from the case mouth to the freebore. If they see that kind of transition, their first action would be to contact the customer (company having barrels made) and let them know the reamer design has an error, if it was actually present.
There was also a lot of hype where certain segments of the industry saw it as a done-deal for SOCOMs and the USMCs new cartridge, so by trying to ride the coat tails of the new momentum, if they could make themselves notorious by fixing some "inherent problem with the design", they could cement their legacy in the history of US small arms.
Ramshot Powders tested the 2 different chambers (SAAMI and SPC II) on their instrumented test breach and barrel, and found maybe 30fps difference. They started with the SAAMI chamber, fired their pressure-tested strings, then reamed it to SPC II and repeated. They got 20-30fps difference with less than 1000psi change in peak pressure. 6.8 forum called foul, said that one of the biggest powder manufacturers with decades of pressure test experience and SAAMI compliance institutional knowledge was doing it all wrong.
There is so much that went on behind the scenes with 6.8 development that has never really been in the open. The consumer can rest assured now that only safe ammunition is produced by the current go-to companies like Federal, Hornady, Nosler, Remington, and Sellier & Bellot.
There are still some guys that think the industry screwed it all up, and that you can chase the .270 Winchester velocities (which has twice the case volume and 65,000psi working pressure from large actions meant to handle it) with 6.8 SPC II Mod X with the right combination of secret sauce and special tweaks to rifling, twist rate, freebore, COL longer than 99% of the magazines out there, etc. There was a guy that was getting over 2820fps with a 130gr from his 22 6.8 SPC II clipping his mags and loading long, claiming that a combination of the secret sauce allowed him to do this safely.
I looked at my .270 Winchester loads pushing 130gr and 135gr at similar same speeds and wondered what I was doing wrong!
The last thing you want to do is make a cartridge perform to a set of unrealistic expectations like that. It drives you to substitute caution with bravery when at the load bench and behind the rifle.
When I did my first ladders with CFE223 under the 123gr A-MAX in Grendel, I reached some stupid velocities well above what I expected (which departed from the trend line of course). Imagine if I came on here and said, Guess what guys! 2700fps with a 123gr from a 16 Grendel is totally doable. Work up your own load of course, but this is what Im getting!
For the hunter or prepper, you wont see a practical difference within 150yds between the 2 cartridges. For those that think they can safely load past 55,000psi with a larger case head in standard AR-15 barrel extensions, I would advise to lean towards caution instead of chasing mv.
One chamber would be more ideal for accuracy looking to fulfill the DMR/SPR solicitation that SOCOM was looking for. (That award ended up being the .223 Wylde SPR shooting 77gr SMKs from 5.56 cartridges, not anything 6.8x43). The 6.8x43 DMR chamber actually had a tighter freebore than projectile diameters, but it sure was accurate!
Another chamber was meant to allow more velocity since the SEALs wanted the 115gr going 2900fps, but nobody could safely reach those velocities of course, even after promising the SEALs that it was no problem". Several tried and blew up a lot of guns in the process at some very well-known companies.
Then there was another chamber that was supposed to be a balance between the 2.
SSA loaded at least 3 different pressure levels, 2 of which exceeded what the action will handle in volume, and this was demonstrated across a fleet of rifles with predictable results, all resulting in failure of critical pressure-containment components.
Ive heard a more detailed account of what happened with the SAAMI submission. I'll just say that no reamer maker worth their salt would purposely make a reamer with an unsafe hand-off from the case mouth to the freebore. If they see that kind of transition, their first action would be to contact the customer (company having barrels made) and let them know the reamer design has an error, if it was actually present.
There was also a lot of hype where certain segments of the industry saw it as a done-deal for SOCOMs and the USMCs new cartridge, so by trying to ride the coat tails of the new momentum, if they could make themselves notorious by fixing some "inherent problem with the design", they could cement their legacy in the history of US small arms.
Ramshot Powders tested the 2 different chambers (SAAMI and SPC II) on their instrumented test breach and barrel, and found maybe 30fps difference. They started with the SAAMI chamber, fired their pressure-tested strings, then reamed it to SPC II and repeated. They got 20-30fps difference with less than 1000psi change in peak pressure. 6.8 forum called foul, said that one of the biggest powder manufacturers with decades of pressure test experience and SAAMI compliance institutional knowledge was doing it all wrong.
There is so much that went on behind the scenes with 6.8 development that has never really been in the open. The consumer can rest assured now that only safe ammunition is produced by the current go-to companies like Federal, Hornady, Nosler, Remington, and Sellier & Bellot.
There are still some guys that think the industry screwed it all up, and that you can chase the .270 Winchester velocities (which has twice the case volume and 65,000psi working pressure from large actions meant to handle it) with 6.8 SPC II Mod X with the right combination of secret sauce and special tweaks to rifling, twist rate, freebore, COL longer than 99% of the magazines out there, etc. There was a guy that was getting over 2820fps with a 130gr from his 22 6.8 SPC II clipping his mags and loading long, claiming that a combination of the secret sauce allowed him to do this safely.
I looked at my .270 Winchester loads pushing 130gr and 135gr at similar same speeds and wondered what I was doing wrong!
The last thing you want to do is make a cartridge perform to a set of unrealistic expectations like that. It drives you to substitute caution with bravery when at the load bench and behind the rifle.
When I did my first ladders with CFE223 under the 123gr A-MAX in Grendel, I reached some stupid velocities well above what I expected (which departed from the trend line of course). Imagine if I came on here and said, Guess what guys! 2700fps with a 123gr from a 16 Grendel is totally doable. Work up your own load of course, but this is what Im getting!
For the hunter or prepper, you wont see a practical difference within 150yds between the 2 cartridges. For those that think they can safely load past 55,000psi with a larger case head in standard AR-15 barrel extensions, I would advise to lean towards caution instead of chasing mv.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com