HK 91 STRIPES ON FIRED BRASS

[shotdown61]

Got back from the range tonight and while picking up brass I noticed the brass from another shooters HK 91 had stripes and also looks like powder burn all the way to the rear of the brass.
Anyone know if this is normal or is there a problem with his chamber.
I have never see anything like this before and just had to bring it to the attention of the shooter.
He also did not know but was told most people will not use the brass over for reloading.
Any thoughts?

[Helen Keller]

yea. that's what the fluting does since the case floats on the gas.




They're fine for reloading long as they don't get all munched up on ejection.

[shotdown61]

So there is fluting in the chamber itself?It was getting dark so didnt bother to look.
The guy will be pleased to hear this.Looked like a nice rifle.

[deth502]

cutaway view

[shotdown61]

Thanks deth.Is this a HK thing or common on other rifle makers?
What is the purpose for the fluting?

[imanaknut]

I have an MP5 and it seems to be something H&K likes. It does get some funny looks from people who pick up the spent shell and see the H&K racing stripes!

[Silicon Wolverine]

my CETME does the same thing. if the ammo is on teh hot side it will ruin the brass. most of teh time it OK to reload. around 40% of my CETME brass is either crunched or unfit in some other way.

SW

[Schuetzenman]

Thanks deth.Is this a HK thing or common on other rifle makers?
What is the purpose for the fluting?

This is an HK thing as it's the only way their delayed blow back roller lock up bolt system can extract a spent casing. Fill in the chamber flutes and the HK becomes a single shot. Certain South American surplus rounds had a tar based bullet sealant, these would in fairly short order fill in the flutes and the weapons would stop cycling.

[mriddick]

The SVT40 also has flutes. The flutes do not hurt reloading although it's not uncommon for delayed blowback rifles to stretch cases more then locked actions and this needs to be watched.

[shotdown61]

This is an HK thing as it's the only way their delayed blow back roller lock up bolt system can extract a spent casing. Fill in the chamber flutes and the HK becomes a single shot. Certain South American surplus rounds had a tar based bullet sealant, these would in fairly short order fill in the flutes and the weapons would stop cycling.

Interesting.But couldnt this set-up be less reliable?Carbon build up,dirt,any obstruction to the flutes could cause the rifle not to function properly.

[Solidus-snake]

In a way, the high pressure gases help keep the flutes clear of obstructions so I've been told. I would test it with my CETME, but ammos too damn high lol.

[Schuetzenman]

Interesting.But couldnt this set-up be less reliable?Carbon build up,dirt,any obstruction to the flutes could cause the rifle not to function properly.

Theory says yes, reality (baring tar bullet sealant) says no. I've owned CETME and HK clones and they ran just fine for as long as I was willing to shoot them before cleaning. These weapons are however sensitive to low power ammo. If the ammo is too low pressure / slow the weapons will short cycle and not completely eject the spent case or they will eject but not pick up the next round. The only surplus I ever shot in one that gave problems was Chillean surplus 7.62 N ammo. Portuguese, DAG, FN even Radway Green all cycled them just fine. Cleaning the chamber is part of the cleaning process. AS mentioned by Soldius, the high pressure of the gases help to flush them out and keep them open.

[deth502]

This is an HK thing as it's the only way their delayed blow back roller lock up bolt system can extract a spent casing. Fill in the chamber flutes and the HK becomes a single shot.

^this

the function of this rifle is completely unlike a gas operated gun, although, by definition , thats what it is. in a typical gas gun, nothing moves untill the gas enters the gas port, by which time the pressure has already dropped. then, when th gas does enter the gas system, it begins by acting on the arrier, and there is another signifigant delay before the bolt itself is actually acted on. by this time the chamber pressure is nearly nill. of course, you know how a brass case works, right? the pressure of the propellant forces it tight to the chamber walls and seizes it in there to form a gas seal. key thought there being the case is actually seized to the chamber wals when the propellant is pressurizing the chamber.

in a roller delayed system, the case itself acts as the gas piston. as soon as the cartridge is ignited it begins moving. in the begnning of development for the cetme, the chambers were not fluted. when the case seized to the chamber walls, and the extractor began moving backward at the same time, the case was ripped apart, alowing hot high pressure gases to escape through the action causing catastrophic failures. they solved this problem by issuing ammo that was ompletely coated in a heavy grease. this grease lubed the chamber walls preventing the casing from seizing to the chamber walls and therefore allowing extraction without case separation. im sure you can imagine how well that would work in the field. not only trying to handle greased rounds, load them into magazines, stor them without the grease drying out or melting off, and not to even get started on the dirt attracting qualities of a wet greased casing. needless to say, it was a clusterfuck. in order to overcome this, they fluted the chambers. the high pressure gas that launches the bullet, and pushes the casing out to seize to the chamber walls, was now allowed to go around the case mouth, and enter into the chamber walls, equalizing the pressures from the inside of the casing to the outsede, therefore, not allowing it to seize to the chamber under the high pressure of the propellant charge and instead "floating" it in the chamber.

[davepool]

I've picked up brass that looked like that at the range and couldn't figure out what caused it; for that matter, i didn't know what a delayed blowback system was or how it functioned unitl now...THANKS, i are smarter now.

[Helen Keller]

Dont' use polymer or aluminum cased ammo in any HK style weapon, you'll lose your mind.

And sure as hell don't use Indian .308 if you have a 91/G3 . The tar/crap residue will plug the flutes FAST usually under 200 rounds.

[El Laton Caliente]

I'd add that thinner walled, softer commercial .308Win can cause problems that 7.62x51NATO spec loads will not. As I recall, only the PTR91 is truly rated for both. The G3's, CETMEs and HK91s are rated for mil spec ammo.

I've seen more damage from not having a port buffer than from the flutes as far as reloading goes. Neck openings get damaged on ejection a lot. You can get a port buffer or glue a piece of 1/8" rubber at the back of the ejection port and get less damage to the casings. The other thing is to check case length before reloading.

[gpwasr10]

Got back from the range tonight and while picking up brass I noticed the brass from another shooters HK 91 had stripes and also looks like powder burn all the way to the rear of the brass.
Anyone know if this is normal or is there a problem with his chamber.
I have never see anything like this before and just had to bring it to the attention of the shooter.
He also did not know but was told most people will not use the brass over for reloading.
Any thoughts?

Perfectly Normal... the design is not known to be a "re-loaders rifle".

[MJ1]

I have 400 CAVIM 7.62 cases on their 8th reload. No problems. I have 300 LC 88 5.56 cases on their 4th reload. No problems.



...........Cheers..................

[Schuetzenman]

Surprised the Cavim cases can still hold a primer in the pocket.

[gpwasr10]

MY PTR-91 beat the high holy hell out of my brass.