6.8x51 sig hybrid case section view.

[someguy2800]

I got some 6.8x51 sig hybrid cases from American Reloading to play with. 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 thought I read they were using an aluminum locking ring to hold the head on, but as you can see there is no such thing, the brass is just 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 formed. 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



I am really interested in building a bolt action rifle in this cartridge but right now their aren’t many good high BC bullets in .277 caliber in the weight range I’m interested in. I formed 50 of them to 308 and I’m going to try loading them and see what happens. If they work well I’m thinking about maybe making a 284 sig fury wildcat to take advantage of the additional case capacity and improved shoulder over 7-08. If the army sticks with this deal I expect there will be cheap and abundant cases for many years to come.

 

[adcoch1]

I see primer failures in our future.... But other than that, it's an interesting idea. How far above standard pressure do you plan on experimenting to? I would assume proof loads are reasonable...

 

[someguy2800]

I see primer failures in our future.... But other than that, it's an interesting idea. How far above standard pressure do you plan on experimenting to? I would assume proof loads are reasonable...

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. I’ve done some number crunching in quickload and going from 65,000 to 80,000 is not really that big of an improvement.

 

[someguy2800]

Lake city 7.62 nato case weight



LC 7.62 water capacity



Hybrid case weight



Hybrid case water capacity (formed to 308)

 

[small town life]

QL has the 270-08 or 27-08 or 270/308, don't remember which it was listed as before the 6.8x51 was a thing? I thought the cartridge would be an improvement over the 308win/7.62x51 with the higher bc 150, but velocity was lower than the 308win. The hybrid 6.8 uses a 135gr iirc. 1 day I'll chamber (using brass cases only) for up to ~62k (308win max pressure). This way I can shoot 150's in 26, 27, 28 and 30cals (already have 150's for 26, 28 & 30cal). I can't leave my 6.8spc by itself, so awaiting on 6.8x51 someday?

 

[small town life]

I've seen brass (and hybrid) cases for sale on ammoseek and wikiarms for the 6.8x51.

 

[someguy2800]

QL has the 270-08 or 27-08 or 270/308, don't remember which it was listed as before the 6.8x51 was a thing? I thought the cartridge would be an improvement over the 308win/7.62x51 with the higher bc 150, but velocity was lower than the 308win. The hybrid 6.8 uses a 135gr iirc. 1 day I'll chamber (using brass cases only) for up to ~62k (308win max pressure). This way I can shoot 150's in 26, 27, 28 and 30cals (already have 150's for 26, 28 & 30cal). I can't leave my 6.8spc by itself, so awaiting on 6.8x51 someday?

My version of quickload has 277 sig fury in it.

 

[someguy2800]

Expanding on what I mentioned earlier about the 80k psi not making that much difference. What I e found playing in quickload is that in 308 class cartridges with 20+ inch barrels it doesn’t make for huge velocity improvements. In my 21.2” 308 barrel in only predicts 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 quickely peters out.

 

[small town life]

My version of quickload has 277 sig fury in it

Which version is it? I haven't checked thru the 27cal stuff lately since the July (forgot which year) update.

 

[someguy2800]

Which version is it? I haven't checked thru the 27cal stuff lately since the July (forgot which year) update.

I’d have to check, I got it just over a year ago.

On a side note, the sig round is not quite the same as a 270-08. The shoulder is pushed forward and a steeper angle. Water capacity is 55.3 grains

 

[Speedo66]

80K psi?

I see the VA having a slew of hearing loss cases.

 

[someguy2800]

80K psi?

I see the VA having a slew of hearing loss cases.

Given the same case volume, a higher peak chamber pressure will actually have a lower muzzle pressure because if you make the pressure curve spike earlier by using faster burning propellent, the pressure will also taper off sooner. They are also putting a suppressor on all these rifles as standard issue.

 

[small town life]

I’d have to check, I got it just over a year ago.

On a side note, the sig round is not quite the same as a 270-08. The shoulder is pushed forward and a steeper angle. Water capacity is 55.3 grains

I have 3.9version that does have the 277fury. Case lengths are the same, but doesn't show specs on the 270-308. 30* shoulder on the 277 and possibly 20* on the 270-308? Probably adds body length to the 277?

 

[bfoosh006]

Thank you , Sir.
Did the cases have some powder stuck in them ?
Amer. Reloading says they do.

 

[someguy2800]

I have 3.9version that does have the 277fury. Case lengths are the same, but doesn't show specs on the 270-308. 30* shoulder on the 277 and possibly 20* on the 270-308? Probably adds body length to the 277?

Here is the saami drawing for 277 fury and 308. The 277 is .125 longer to the body shoulder junction

 

[someguy2800]

Thank you , Sir.
Did the cases have some powder stuck in them ?
Amer. Reloading says they do.

Yes they all do. Maybe 1-3 grains of ball powder each. It’s just static clung to the inside, not compressed or anything.

 

[bfoosh006]

Yes they all do. Maybe 1-3 grains of ball powder each. It’s just static clung to the inside, not compressed or anything.

Thank You.

 

[someguy2800]

Got my new rifle in 308 and shot the first 30 rounds today in the sig hybrid cases.

This was round 6-10 after sighting in at 100 yards



Here is a 15 round group and as you can see there were no significant flyers



The load was 46 grains of N140 with a 150 grain SST and Win LR primer.

 

[someguy2800]

 

[bfoosh006]

That is great shooting ! I would be quite proud of those groups.

Any details on the rifle itself ?

 

[someguy2800]

That is great shooting ! I would be quite proud of those groups.

Any details on the rifle itself ?

It is a Lithgow LA102 with a burris 2-10x42. I’m sure it will shoot better than that with load development and trying harder.

 

[Walkalong]

Sweet looking rifle.

 

[someguy2800]

Sweet looking rifle.

Thanks, I got their rimfire version in 17 HMR a few years ago and I’ve been wanting to try the centerfire version too. That one is a real shooter too





I like the 308 one so much I ordered another that I am planning to rebarrel in 338 weatherby rpm and I’m thinking of selling a couple of my other rifles and picking up a third. The rimfire ones take CZ magazines and the centerfire take Tikka magazines.

 

[Nature Boy]

This has been fun to follow. Those cases should last forever.

I’ll be curious to know how much the cases grow and how much you’ll have to trim

 

[Gtscotty]

Was it just one pass through a .308 die to get the 6.8 sized to .308, or did you have to go in stages? I'm thinking these might be a good fit for my SFAR that's rough on case heads. I'd also be curious how hard it is and what's involved to form these to 6.5 Creed. I have a Sig Cross in 6.5 and I'm a little tempted to experiment with 6.5 Fury type loads.