Ok, how is SIG making hybrid ammo?

[cyanidekid]

How is SIG or their partners making stainless -brass cartridge cases for the .277 ? From a material strength standpoint it makes sense, but cranking out millions of them.. well seems nuts. Anyone have some Metallurgical how it’s done?

 

[FamilyTradition]

I don't think there's much in terms of metallurgical magic involved with it. If you look at the diagram on this article: https://www.all4shooters.com/en/hun...rid-cartridge-the-cross-in-277-fury-277-fury/

It looks like the brass and steel are stamped and drawn separately, then mechanically fastened together.

 

[plastikdreams]

Says it's a stainless base coupled to a brass body using an aluminum locking ring...

 

[DDoug]

Says it's a stainless base coupled to a brass body using an aluminum locking ring...

Might be using this:

Electromagnetic Forming Technology

Assembly process can be used wherever components need to be joined, assembled, or formed to specific shapes.

elmaginc.com

 

[GGaskill]

I wonder if those cases are reloadable. The aluminum Blazer cases aren't.

 

[jmm03]

I wonder over time if there will be a dissimilar metals reaction.

 

[cyanidekid]

ahh, ok, so its a full(ish) brass case, with a rebated rim and a reinforcing "back cap". still wonder how the assembly is done, guess the stainless base can be deformed or "closed" around the locking ring. seems it would have springback tho... I'd like to see the presses and dies.

 

[cyanidekid]

I wonder if those cases are reloadable. The aluminum Blazer cases aren't.

since it's a full length (or nearly) brass case, I don't see why not. don't know how replaceable the primers would be, but they look like a "cup" type just bigger, so seems likely.

 

[MilGunsmith]

We are testing these daily here at work. The current case design is two piece, they have done away with the locking ring. The brass is swaged onto the stainless steel base. I just sectioned some for a display.

 

[MilGunsmith]

Here is a picture of the cutaway brass. You can see the two pieces swaged together.

 

[GGaskill]

I guess that recurve at the very bottom is what prevents case separations.

 

[john.k]

Funny,but amateur collectors and shooters have been using exactly the same method of joining brass tube to steel bases to make obsolete cases since I was a child.........The system was invnted and patented by Col. Edward M Boxer RE in 1864,in relation to the conversion of muzzle loading rifles to Sniders patent system of breech loading.

 

[cyanidekid]

ok, that makes a whole lot more sense than aluminum locking rings. are those standard large rifle primers or proprietary?

 

[john.k]

people have been making rifle cases from drawn steel for over 80 years ......in fact much european military ammo is all ferrous ...no brass at all,not even primers...........so how does this process have any cost advantage over steel cases?

 

[GGaskill]

Plain steel cases wouldn't cost much. Composite ones will cost lots more, hence, more income for the producer. : - )

 

[MilGunsmith]

ok, that makes a whole lot more sense than aluminum locking rings. are those standard large rifle primers or proprietary?

I know that they are a standard large rifle primer size, but I haven't checked the thickness yet. They do not appear to be crimped or staked either.

 

[M. Roberts]

If a cartridge is fully contained in the chamber, and backed up by the bolt (thinking a rifle), then what would be wrong with making the cartridge out of plastic? I know this is going to get some people fired up....just a question...

 

[MilGunsmith]

We have tested plastic cases here for over 20 years. We can get them to function well in a non-automatic use, but they fail in the full automatic guns. Usually case separations in various locations. We have even had some versions fail in testing in the Universal Receiver, which is a big solid falling block action with minimum dimension chambers.

 

[cyanidekid]

If a cartridge is fully contained in the chamber, and backed up by the bolt (thinking a rifle), then what would be wrong with making the cartridge out of plastic? I know this is going to get some people fired up....just a question...

if brass isn't strong enough to contain the hypercharge this round takes (80,000 range), well, how do you think plastic would do?

as to why not steel cases, ill note the base is stainless. it wouldn't be practical to deep draw the entire case from stainless. I presume corrosion resistance is a requirement.

also, do steel cases cause problems for durability of guns in full auto, particularly in SAWs and LMGs?

 

[kopcicle]

The tremendously oversimplified details are, in no particular order:

The elevated pressures were overwhelming the primer pocket.
The solution was a stainless steel case.
Stainless steel is not as ductile as brass so there were issues with incomplete obturation of the case under pressure and subsequent leakage of combustion gasses from the chamber.
This resulted in a hybrid case with a stainless base to better support the primer and a brass body to better seal the breech pressure.

Examining the several cutaway section photographs and being somewhat in the know from association with previous efforts, the connection between brass and steel only improves under pressure.

Completely subjective thoughts.
This case should be easier to produce than a conventional coin, cup, and deep draw cartridge case. The base can be easily and repeatedly turned on a CNC lathe and the brass portion can now be made from brass tubing. Dimensional stability while forming tube while having access to both ends makes this a relatively easy process when compared to the previous coin, cup, and deep draw methods. This could be adapted to continuous feed turning centers with little if any new technology or processes.

Now designing a Model 700 clone that shrugs off the reported 80,000 psi chamber pressures with a safety margin? This is about the ammunition anyway. and Sig bless their hearts have supported the ammunition with yet another US government contract to produce a weapon.