The H&K G3 (or CETME),as it fires,the case starts to move back,it moves the bolt back/force the rollers in/seperate the carrier from the head/and so on,as the case starts move back and out of the chamber,doent the psi make the case blow up out of the chamber,or is it so fast that by the time the case is part out of the chamber the bullet is long gone out the barrel and the psi is down?



Actions: Blowback Action: Roller Delayed Blowback

I don't know about CETME's, but HK's have the chambers edm'd in, not reamed. That leaves the chamber walls faceted, to facilitate extraction. A fired case out of my 53 will have lines running the length of the brass, and when you spin that case in your fingers you can feel the multi facets.   Beyond those facets the case is not damaged and can be reused.  On another note, my SR25 demolishes brass. It is one of Knights early rifles and when fired the case evidently is still very "attached" to the chamber walls. The extracted case has a head that is twisted/rotated, the extractor and ejector cutouts in the face of the bolt have swedged material off the head of the case, and they are pretty much junk after that. I guess it IS true...........timing is everything.

Actually, in your lower picture.......where it shows the case partially extracted, you can see the drawing shows a faceted chamber (shows in the neck area of that drawing)

The H&K G3 (or CETME),as it fires,the case starts to move back,it moves the bolt back/force the rollers in/seperate the carrier from the head/and so on,as the case starts move back and out of the chamber,doent the psi make the case blow up out of the chamber,or is it so fast that by the time the case is part out of the chamber the bullet is long gone out the barrel and the psi is down?


Correct the delayed roller block is like any other system in that the brass expands to mold to  the chamber upon detonation.  But in the case of the Cetme / G3 system the chamber is fluted and thus you will get flutes or indentations in the brass from the brass expanding in the flutted chamber.  Make sense ?

ETA:  If everything is in sync, the proper bolt gap will allow a delayed separation of the Bolt Head from the carrier.  During that delay the case expands, then is withdrawn from the bore and expanded or extracted and ejected.

This is probably a question best answered by HKpro ~ as far as I understand the process, the fluted chamber floats the case to propel it backwards ~
the bullet is almost already gone, but the locking piece provides a calculated amount of resistance, where by the bulk of the force is already taxed on
the bolt group just as the bullet leaves.  This is why there are locking pieces and rollers of varying degrees and sizes, and why especially in a 308, the
carrier continues to have such a impact on the rear of the gun, necessitating two push pins vs one on the lighter calibers.

The larger the flutes, the more reliable the action, but potential for slightly lower accuracy.  It's the only action (except for HK G36 based actions) that
survive brutal desert testing.

Most of the soot is blown back into the chamber face and rear of the trunion ~ ergo they are so so filthy to clean, but run very well.
But they do need their oil!  Learned the hard way, didn't oil the trigger pack and it wouldn't function, a few drops of ballistol and it ran like
no one's business.

They are temperamental, springs and small parts fail and wear out, much more so than on an AR.

In a gas system,case extraction is "softer" in the case as the carrier moves back forced by the gas over the piston/rod,gas recoils the bolt to unlock and extract,with a delayed blowback,the bolt opening and case extraction start wth the case,all the gas force moves inside the case,ths makes the case expand inside the chamber and as to open the bolt the case as to move back/out...the fluted cuts make the case extraction softer as if with no cuts tha gas psi can brake the case as the neck is tight in the chamber,ths was a problem with the STG45...but tha case as to move back so the bolt can start to unlock,does the case hold its position inside the chamber using expanding gas psi inside it alone...?





For the bolt to start "unlocking" it as to move back,with a gas system the gas moves the carrier back,but with a delayed blowback the case as to move back so the bolt can move back as the rollers and head/carrier seperation delay only the full openng of the bolt...but to start the delay it as to move back and it moves back only when the case starts to move back...so...does the case hold its position with tha gass pst expanding inside it but also forcing it back/out?...

...for the bolt to move back,tha case as to move back/out of the chamber with psi inside the barrel,as it starts to move out of the chamber doesnt the psi expanding inside (and forcng it back) expand inside up to the point of exploding or deforming the case in that unprotected part out of the chamber?

Every delayed blowback system starts to "unlock" wth gas psi inside the barrel...



http://www.thefirearmblog.com/blog/2013/01/01/do-you-know-your-hks-parents/

The function of this rifle is completely unlike a gas operated gun, although, by definition , that's what it is. in a typical gas gun, nothing moves until the gas enters the gas port, by which time the pressure has already dropped. then, when the gas does enter the gas system, it begins by acting on the carrier, and there is another significant delay before the bolt itself is actually acted on. by this time the chamber pressure is nearly nill. 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 walls 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 beginning 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, allowing hot high pressure gases to escape through the action causing catastrophic failures. they solved this problem by issuing ammo that was completely 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, store 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 outside, therefore, not allowing it to seize to the chamber under the high pressure of the propellant charge and instead "floating" it in the chamber.

http://www.gunsnet.net/showthread.php?17928-HK-91-STRIPES-ON-FIRED-BRASS

Someone here said that the case forms to the flutes in teh chamber.  When I had both a CETME and an HK91, I wondered about this, and played with a few spent shells.  I found that the case didn't actually form to the fluting, but it was pretty dirty from the carbon in teh gases that flowed down teh case in the fluteing.  The only deformation on the brass I really saw was with my CETME; damn it would munch the neck on the brass pretty bad from hard ejections.

"the case itself acts as the gas piston" good definition,having a lubricated case as problems but did it worked when extracting the case or the problem still existed,can the use of a dry lubricant surface treatment solve the broken case problem or is it the use of a fluted chamber the only practical soluton for ti?

The case problem existed back in the days when they changed the STG45 from a short recoil piston/rod system to a delayed blowback system,the fluted chamber was the solution.

It may not deform the case as the gas expanding outside the case (inside the fluted cuts in the chamber) as the gas expanding inside the case so thet is why the fluted marks on the case may be from the filt acumulated on the chamber fluts and case wall after every shot.

I have to assume the Flutes were the most practical solution for it.  The greased ammo just conjures up all sorts of nightmares even if it worked.  Same I would assume dry lube.  This book would be a great addition to anyones firearms library.

http://www.collectorgrade.com/bookshelf8.html

CETME LMG,no fluted chamber on th drawng...

The best way to say is that the fluted cuts in the chamber are for the gas and not for the case...for the gas vent in to but not for the case expand to...

CETME patent drawing,tha case is forced back,out of the chamber,with high gas pis inside it,pat of it is no longer protected by the chamber,why doesn't it explode?

Because there is just enough delay cause by the rollers to allow the gas to escape.

"In order to drive the bolt carrier with the increased velocity during the unlocking period, the G3 bolt system does not have a lever, but an angular transmission, installed symetrically to the axis of the bore, with two rollers as transmission elements.

The ratio of the bolt head carrier with the locking piece travels backward four times faster than the bolt head, and only as long as the rollers move on the inclined surfaces of the barrel extension and locking piece"



http://www.hkpro.com/index.php?Itemid=5&catid=4:special-topics&id=133:technical-engineering-detail-of-the-g3&option=com_content&view=article

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