Purpose of "Fluted" HK-91 or Cetma chamber????
- Thread starter vtmarmot
- Start date
The cases can be reloaded just fine. I've reloaded hundreds of them for my HK-91. Use a small base die and tumble the cases with stainless steel pins before resizing. They'll be fine. [br]
HK roller-locked weapons use a development of Edward Stecke's patent. The bolt head, while bore pressure is still high, exerts pressure against both the firing pin carrier and the barrel extension locking abutments. The bias is toward the firing pin carrier, which is forced to the rear, along with the bolt carrier, and allows the rollers to move inward and the bolt to unlock from the barrel extension. All this occurs with high residual bore pressure. This would normally cause severe extraction problems because of the case being forced against the chamber walls. The flutes, very shallow grooves arrayed around the chamber and whose depth tapers to nothing toward the chamber rear, allow propellant gas to "float" the case free of the chamber walls and to be extracted. Examine case rims for extractor marks and you will see that they still do not come too willingly. The action is violent and very fast, often throwing cases thirty feet or more. But, it also continues to function when dirt is in the action. It is an excellent system; simple, reliable and robust.
HK roller-locked weapons use a development of Edward Stecke's patent. The bolt head, while bore pressure is still high, exerts pressure against both the firing pin carrier and the barrel extension locking abutments. The bias is toward the firing pin carrier, which is forced to the rear, along with the bolt carrier, and allows the rollers to move inward and the bolt to unlock from the barrel extension. All this occurs with high residual bore pressure. This would normally cause severe extraction problems because of the case being forced against the chamber walls. The flutes, very shallow grooves arrayed around the chamber and whose depth tapers to nothing toward the chamber rear, allow propellant gas to "float" the case free of the chamber walls and to be extracted. Examine case rims for extractor marks and you will see that they still do not come too willingly. The action is violent and very fast, often throwing cases thirty feet or more. But, it also continues to function when dirt is in the action. It is an excellent system; simple, reliable and robust.
[br]M-61 said:
wrong
hoz53
Gold $$ Contributor
Wow I've learned some more thanks to this site. I to thought the flutes in an HK chamber were to grip the case and slow the bolts opening motion. Now I know how the system really works. Thanks sleepyG. Also interesting seeing that sectioned fluted chamber. Thanks groc. I just wish I hadn't sold my HK 93. I'm sure it's been reincarnated as an MP-5. Would be interesting to know the path it's taken.
Yup exactly the opposite. They allow gas to flow around the case to allow it to extract even under high pressures. I love the roller delayed blow-back design from a reliability standpoint. The thing I dont like about HK-91s, the stock. Put your head where it should be for an appropriate view of the sights and you get a wonderful black eye as a souvenir.
Ah .... you lucky people. Fight hard to keep your HK91s. We in the UK lost the right to ours and every other semi-auto and pump-action rifle other than .22 calibre rimfires on 1st April 1989 as a consequence of a psychopath killing people with an AK in the small town of Hungerford the previous year. Semi-auto military type rifles were just becoming popular and the HK91 was a prime choice for those who aspired to something more expensive than a surplus FAL. It was always easy to recognise discarded brass on the ranges from the fluting marks which sometimes became more pronounced after the case had been lying in the wet for a while and started to oxidise. I would think 99.9% of owners used the dirt cheap surplus military 7.62mm ball ammo that every gunshop stocked back then and many didn't bother recovering their spent brass.
As always, Sleepygator's description of the process is spot-on. I'd only add the HK roller-locking breechlock system is officially classified as 'semi-blowback' or 'delayed blowback' hence the need for the case to be 'floated' in a thin layer of deliberately escaped gas between it and the chamber walls.
The description of the violence of the system's ejection made me smile too - a member of a club I joined back in '86 had owned an HK, but sold it before my time. Even today, whenever this character's name comes up, old club members reminisce about "that bl**dy HK" that he'd owned and would pepper them with high-velocity, and very hot fired cases. After a while he was banned from using it unless the extreme right hand end of the range's cramped firing point was free.
What I did sometimes wonder is how much work is needed to get the chamber clean afterwards?
As always, Sleepygator's description of the process is spot-on. I'd only add the HK roller-locking breechlock system is officially classified as 'semi-blowback' or 'delayed blowback' hence the need for the case to be 'floated' in a thin layer of deliberately escaped gas between it and the chamber walls.
The description of the violence of the system's ejection made me smile too - a member of a club I joined back in '86 had owned an HK, but sold it before my time. Even today, whenever this character's name comes up, old club members reminisce about "that bl**dy HK" that he'd owned and would pepper them with high-velocity, and very hot fired cases. After a while he was banned from using it unless the extreme right hand end of the range's cramped firing point was free.
What I did sometimes wonder is how much work is needed to get the chamber clean afterwards?
People: That is on my short list of dream guns as well. After Reading Tom Clancys Rainbow Six, Ive wanted one. I have shoulder but never shot the HK collapsing stock and turned that rifle down because it wasnt even fun to shoulder it without firing. I got my HK 91 with an A3 stock instead and it was still awefull on the cheek.
GrocMax said:They throw HOT HOT HOT brass in unpredictable directions with AUTHORITY, don't ask me why I know, I still have the scars
Typical German engineering; it's one of the few combat rifles that allows you to simultaneously protect your own right flank while shooting directly ahead!
as long as it's NOT your friends situated on the flank. An ex Royal Air Force non-com I briefly knew years back once told me of his occasional training days on the firing range in which he and other airmen were given some basic training in rifle shooting.
The UK L1A1 version of the 7.62mm FN FAL, known universally in the Brit armed forces as 'The SLR', had only recently replaced the old 303 Enfield. The sargeant instructor started of well in the classroom telling the trainees this is 'the finest rifle in the world', and then proceeded to undo that favourable impression by listing all its faults compared to the Enfield so by the time they got onto the range they were all a bit nervous. Two seconds into live firing and an airman got a neighbour's hot case trapped between his collar and the back of his neck. The burn was bad enough to see him removed to sickbay.
After that, my friend told me that nobody cared about hitting the target on subsequent range days, just bagging the extreme left-hand firing point!
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