Anyone shooting a gun chambered like this?

Score!!!

 

HK 91 uses fluted chamber. The deformation causes the casing to become basically a gas piston.

 

Yep, it’s the only way to get this to happen. Any deformities in the chamber are imaged in the brass after firing. It’s why resizing is the first step in reloading.
Still doesn’t really explain the “why”, though.

 

So are you saying that the brass is ridged before firing?

 

Exactly, I am curious about the why.

 

Now that is out of the way for the time being, Ray, @gosolo , needs to post Orygun crabbing pics....

 

A round shouldn’t go that far into the fluting of a barrel or the fluting of a barrel shouldn’t go that far back into the chambering of a round.

 

Yeah, but how do you resize something like that in a die?

 

One use only I'm thinking.

 

Never seen anything like that. Subd for curiosity sake.

 

I’m gonna say you can’t reload these

 

I've shot HK 91s down in Peru many moons ago. I dont remember the brass being like that. Not saying it's not the case, I just dont remember.

 

No, the chamber itself is fluted. It deforms the round when fired.

 

Great time with my son visiting.
Crabbing, clamming, mushrooming, crawfishing, and a day on the Columbia trying to snag a silver

 

That’s what I thought

 

I stand corrected. It appears it is intended to assist in extraction.

 

I believe that is what i said in post #3.
Thanks for finding the diagram! I hadn’t ever seen anything like it and thought it was worth letting folks get a look

 

Subd because I like beer and my grandson is asleep..

 

...as you get older...memory fades.........

 

Excellent........silvers were never easy to catch

 

Especially when its TBI induced.

 

Gas extraction. Common on HK designs regardless of actual manufacturer.

 

Your avatar is giving me hallucinations.....

 

Gas extraction is quite common on semi auto's, whether shotgun or rifle versions, but nothing like what we are discussing. I think?

 

So the gas blowback hits the cartridge shoulder and forces it rearward out of the chamber? I wonder what kind of deflector knocks it off to the side? Do you know of any videos showing the action in operation?

 

That’s from a CETME or Hk G3 rifle.
I used to have one. They have a fluted chamber.

 

This. I’m not supposing. I’m telling you this is what happens. Chamber is fired to let gas flow around the brass. Helps knock it loose for extraction. Helps with shit brass and bullets in dirty conditions. Brass forms to the chamber and you have what you have.

Hk91... couple other hk rifles.

 

Fluted chamber is common on roller delayed guns. This is to aid extraction by keeping the expanded brass from sticking to the chamber due to fouling or other gunk (flutes reduce the chamber to brass contact area and allow some gas to help blow out the chamber). Fouling also happens quicker on full auto which these were originally designed to be. The system was also meant for thinker mil-spec brass so using commercial ammo may cause the brass to be more deformed and sometimes tear the case on extraction. My PTR91 had a fluted chamber and so does my MP5. The PTR would destroy brass but it’s less noticeable on the MP5 most likely due to the lower pressure of 9mm vs 7.62x51.

 

^^^ This is your answer.

"A good place to start is by getting a firm handle on the difference between roller locked firearms and ordinary direct blowback guns. The latter design setup sees the bolt pushed backward by the pressure of expanding gases at the same time as the bullet moves down the barrel. This blowback action is delayed in a roller locked design. The critical roller locking mechanism acts to keep the bolt closed for a few vital milliseconds after firing. This reduces the pressure in the chamber before the bolt opens and the gun comes out of battery. The advantage? A roller locked gun can have a lighter bolt group assembly and operate more smoothly.

This analogy should make the difference in the two systems clear. Imagine what it would feel like to strap into the passenger seat of an offroader competing in a grueling Baja race. That's direct blowback. In contrast, operating a roller locked gun is like piloting a German sedan down the Autobahn at 160 mph."

Interesting CNC video: