Anyone else using the 277 Sig brass for standard 308-based cartridges?

[HandgunHTR]

There are a couple of threads on other forums discussing this and a few people are trying it out. Just wondering if there is anyone here doing it?

I just ordered 200 of these to try out in my 7-08AI to see if I can squeeze a bit more out of it. Not that I need to, it just seems like it might be a fun project to play around with this summer. And for $36/100 it isn't going to be a huge investment.

 

[Straightshooter1]

There are a couple of threads on other forums discussing this and a few people are trying it out. Just wondering if there is anyone here doing it?

I just ordered 200 of these to try out in my 7-08AI to see if I can squeeze a bit more out of it. Not that I need to, it just seems like it might be a fun project to play around with this summer. And for $36/100 it isn't going to be a huge investment.

Yup, I've been playing with these lately.

Post in thread 'Anyone tried 6.8X51/.277 Fury hybrid cases?'

Jun 14, 2025

As a tinkerer, I just have to play with these hybrid cases.

Went out last week and fire formed 10 hybrid .308 cases with case volume of 56.3 grs H2O and loaded them with 41.7 grs IMR-4064 behind 190 SMK's using the same primers that I removed from them and seated the primers to the same depth as they were originally. Though this was only to fire form them to I could measure their case volume after firing, the chrono data was remarkably good. SD for the 10 shots was 4.7 and the ES was 15 with MV at 2,560 fps from 26" barrel. Group size was surprisingly good too at .552 MOA...

• Straightshooter1

• 

When you get your order, assuming it's from American Reloading, you going to find a mix of case heads, though they'll all be the 277 Hybrid case, each having different case volumes. Here my first 10 that I tested to get a baseline for case volume and powder performance:


The case came to me primed and some of the cases had some unburnt powder granules clinging to the interior walls of the cases. I decapped them to clean them and reused the primes with good results.

Here's where the box of 100 looked like:



Having given them good anneal job (I let the annealing burn the powder out), sizing using plenty of lube and 3 way trimming them, this is what they looked like after a 25 min wet tumble with SS pins:


PS: my last outing with them I loaded up 10 rounds with 168 SMK's and 46 grs IMR-4064 in cases having a volume of 57.7 grs H2O and that gave me 2860 fps (SD: 6.7, ES: 25), but results on target was not particularly good (.679 MOA). No pressure signs with normal ejection and primers looked just fine.

 

[Fuj]

I'm waiting to see someone doing a boosted 30BR and knocking
the twist rate down a few numbers......

 

[HandgunHTR]

Thanks @Straightshooter1. I can't believe I missed that thread when I looked. Good info there and from what I read, it seems like some learning has happened since then. Specifically, a couple of folks are well past the 500 round mark using these and no ringing of the chambers have happened.
How to determine pressure is a concern, but I have a good idea where I am at with my 7-08AI now, using Lapua brass, and I don't plan to push it too much more. I figure I will be in the 70,000-72,000 range. I may use Gordon's Reloading tool or QL to help determine where I am.

All in all, I already have a 700 yard rifle. If I can push it to 800 or 850 yards with brass that is 1/3 the cost of Laupa or Alpha, that is a bonus. Heck, even if I can't as long as I get consistency, the brass is still much cheaper and should last longer as I am on the edge with my Lapua brass.

 

[Varminterror]

I’ve played a little with making 6 Dasher brass, not terribly easy case forming, but once it gets there, I joke about calling it the “6 Crasher,” because I can get 6 Creed speeds with about 75kpsi (QL & GRT predicted). Pretty cool opportunity. Still 6grn less powder than 6 creed, expect a bit better barrel life than Creed, a little less than GT (obviously less than 62kpsi Dasher), same speeds. Eventually, I might shoot a 1 day PRS match with them just to say I did.

Admittedly, I remain concerned with brass life for the 3 piece cases. Not sure I want to abuse the Sig Hybrid brass like I do Lapua and Alpha.

 

[SeabeeKen]

At what pressure does ejector marks show up? What pressure is the rifle tested too?

 

[Varminterror]

At what pressure does ejector marks show up? What pressure is the rifle tested too?

Most manufacturers introducing 7 BC rifles are not making any changes to the rifles and simply chambering existing designs for the new, 80kpsi cartridge.

The bolt thrust of an 80kpsi standard diameter cartridge is slightly less than that of a 65kpsi magnum diameter cartridge, for which these actions have been designed for decades.

The case head is steel, harder than yellow cartridge brass. I haven’t seen ejector marks on any of my case heads. Ejector marks really have not been a good indicator of pressure even in yellow brass cases anyway, so it’s kind of a red herring to chase.

 

[Walt Krafft]

If you get an ejector mark on a hybrid case you are well past 100k psi. Probably close to kaboom past.

 

[Walt Krafft]

Admittedly, I remain concerned with brass life for the 3 piece cases. Not sure I want to abuse the Sig Hybrid brass like I do Lapua and Alpha.

If you have 3 pc cases, you have early prototypes.

 

[Varminterror]

If you have 3 pc cases, you have early prototypes.

Dunno, I haven’t cut any of mine to see if they have the internal steel retaining ring.

The principle stands - the Sig cases are 2 or 3 pieces, with a mechanical separation at the exact place where common brass failures happen. As a mechanical principle, it’s relatively rare for a joint to be stronger than a solid member.

 

[SeabeeKen]

The case head is steel, harder than yellow cartridge brass. I haven’t seen ejector marks on any of my case heads. Ejector marks really have not been a good indicator of pressure even in yellow brass cases anyway, so it’s kind of a red herring to chase

Youre making my point.
Currently, ejector marks in brass is used to determine pressure limit. Brass is softer than steel so how will you determine youve reached 80k in the hybrid? Which will fail first? Rifle or case? Your face is inches away from a lot of schrapnel.
Brass cases show ejector marks between 70-74,000 psi.

 

[Varminterror]

Currently, ejector marks in brass is used to determine pressure limit.

They shouldn't be. Ejector marks are not reliable indicators of maximum pressure.

how will you determine youve reached 80k in the hybrid?

How did you determine you'd reached 55-62kpsi in yellow cartridge brass cases? At your own statement, yellow brass doesn't reveal ejector marks until pressures considerably higher than any previous cartridge standard older than the new 80kpsi cartridges. So you never had any indicator of value in the past, why would you expect to have one now?

Ejector marks are not a viable indicator of operating pressure, and should not be relied upon for yellow cartridge brass cases, steel cases, or hybrid brass with steel caseheads.

 

[troupe]

There are a couple of threads on other forums discussing this and a few people are trying it out. Just wondering if there is anyone here doing it?

I just ordered 200 of these to try out in my 7-08AI to see if I can squeeze a bit more out of it. Not that I need to, it just seems like it might be a fun project to play around with this summer. And for $36/100 it isn't going to be a huge investment.

Keep us posted, looking to do a 7mm-08 AI. Interested in your findings.

 

[Straightshooter1]

I’ve played a little with making 6 Dasher brass, not terribly easy case forming, but once it gets there, I joke about calling it the “6 Crasher,” because I can get 6 Creed speeds with about 75kpsi (QL & GRT predicted). Pretty cool opportunity. Still 6grn less powder than 6 creed, expect a bit better barrel life than Creed, a little less than GT (obviously less than 62kpsi Dasher), same speeds. Eventually, I might shoot a 1 day PRS match with them just to say I did.

Admittedly, I remain concerned with brass life for the 3 piece cases. Not sure I want to abuse the Sig Hybrid brass like I do Lapua and Alpha.

I'm very curious about case life. With my very limited time I've used them, I noted the design on how the body and base are put together and interestingly to me, where that seam is on the outside of the case, the cases I've fired showed what appears to be some tightening up along that seam. But. . . I wonder about the sizing process, whether the pulling the cases out of the die, even though they're well lubed, many times will change the union to eventually pull them apart??? That would not be a good result. . . have a case body stuck in my sizing die. That's an important issue to watch out for when necking up and sizing them the first time.