someguy2800
Member
Creating a new thread here since this is more relevant in the reloading section.
I got some new pulled 6.8x51 sig hybrid cases to play with and have been working on reforming them into 308 and handloading them. I cut one in half to make a section view. If you haven’t heard this is the Army’s new boondoggle to spend all our money on. Uses a hybrid brass and stainless steel case to handle 80k psi chamber pressure.
I’ve done some number crunching in quickload and going from 65,000 to 80,000 is not really that big of an improvement in longer barrels. What I've found playing in quickload is that in 308 class cartridges with 20+ inch barrels it doesn’t make for huge velocity improvements. Quickload prediction for my 21.2” 308 barrel is only about 100 fps gain going from 60k psi to 80k psi. In a 24” 243 it predicts about 150 fps difference. The biggest advantage I see is that it hits its velocity potential in a much shorter barrel. For example a 243 shooting a 105 gr bullet gets to 3000 fps in 16 inches with the fastest powder predicted. At 60k psi it would take a 21.5” barrel to hit the same velocity. At 16” there is a 250 fps difference but the delta quickly peters out.
I’m not really intending to go hog wild on the pressure because I like my face and I suspect accuracy may suffer at the really high pressures. I’m thinking these will allow you to load to the upper end of brass case pressures, like 65,000 psi, but they should last forever because the primer pockets won’t go loose.
The brass case body is swaged into a locking groove in the case head.
I have been playing with forming them into 308 cases. They are very easy to reform and don’t leave any donut in the neck when the shoulder is pushed back to 308 shoulder position so it does not require neck turning to make 308 cases. The necks are pretty thick so it may require neck turning to turn them into 7-08, 260, or 6.5CM. As you can see the shoulder on the 6.8x51 is quite a bit farther forward than 308.
From left to right 308 win, sig case formed to 308, virgin 6.8x51, 6.5 creedmoor case. The body-shoulder junction on the sig case is .125" longer than 308.
Lake city 7.62 nato case weight
LC 7.62 water capacity
Hybrid case weight
Hybrid case water capacity (after forming to 308)
I finally got my new rifle in 308 today and shot the first 30 rounds in the sig hybrid cases.
The load was 46 grains of N140 with a 150 grain SST and Win LR primer, which should be around 60k psi. Right now I am just using up my excessive stock of 308 hunting bullets, but I intend to try some more consistent bullets soon.
This was round 6-10 after sighting in at 100 yards
And here is 10 more rounds into the same group for a total of 15 rounds. I shot the remaining 10 at steel.
So far so good. I don't see any signs of the case head pulling away from the body. I don't see any gas leakage past the joint or the primer pockets. They basically look the same as before they were fired. I will shoot the remaining rounds in this batch of 50 cases tomorrow and I plan to just keep reloading this lot of 50 and periodically inspecting them internally and pulling one piece out of the lot to section in half and inspect how the body joint is holding up.
I got some new pulled 6.8x51 sig hybrid cases to play with and have been working on reforming them into 308 and handloading them. I cut one in half to make a section view. If you haven’t heard this is the Army’s new boondoggle to spend all our money on. Uses a hybrid brass and stainless steel case to handle 80k psi chamber pressure.
I’ve done some number crunching in quickload and going from 65,000 to 80,000 is not really that big of an improvement in longer barrels. What I've found playing in quickload is that in 308 class cartridges with 20+ inch barrels it doesn’t make for huge velocity improvements. Quickload prediction for my 21.2” 308 barrel is only about 100 fps gain going from 60k psi to 80k psi. In a 24” 243 it predicts about 150 fps difference. The biggest advantage I see is that it hits its velocity potential in a much shorter barrel. For example a 243 shooting a 105 gr bullet gets to 3000 fps in 16 inches with the fastest powder predicted. At 60k psi it would take a 21.5” barrel to hit the same velocity. At 16” there is a 250 fps difference but the delta quickly peters out.
I’m not really intending to go hog wild on the pressure because I like my face and I suspect accuracy may suffer at the really high pressures. I’m thinking these will allow you to load to the upper end of brass case pressures, like 65,000 psi, but they should last forever because the primer pockets won’t go loose.
The brass case body is swaged into a locking groove in the case head.
I have been playing with forming them into 308 cases. They are very easy to reform and don’t leave any donut in the neck when the shoulder is pushed back to 308 shoulder position so it does not require neck turning to make 308 cases. The necks are pretty thick so it may require neck turning to turn them into 7-08, 260, or 6.5CM. As you can see the shoulder on the 6.8x51 is quite a bit farther forward than 308.
From left to right 308 win, sig case formed to 308, virgin 6.8x51, 6.5 creedmoor case. The body-shoulder junction on the sig case is .125" longer than 308.
Lake city 7.62 nato case weight
LC 7.62 water capacity
Hybrid case weight
Hybrid case water capacity (after forming to 308)
I finally got my new rifle in 308 today and shot the first 30 rounds in the sig hybrid cases.
The load was 46 grains of N140 with a 150 grain SST and Win LR primer, which should be around 60k psi. Right now I am just using up my excessive stock of 308 hunting bullets, but I intend to try some more consistent bullets soon.
This was round 6-10 after sighting in at 100 yards
And here is 10 more rounds into the same group for a total of 15 rounds. I shot the remaining 10 at steel.
So far so good. I don't see any signs of the case head pulling away from the body. I don't see any gas leakage past the joint or the primer pockets. They basically look the same as before they were fired. I will shoot the remaining rounds in this batch of 50 cases tomorrow and I plan to just keep reloading this lot of 50 and periodically inspecting them internally and pulling one piece out of the lot to section in half and inspect how the body joint is holding up.
