Powerfull rounds with bullets heavier than 7Grams, use two main systems to manage the breechbolt opening after the projectile to go out the barrel; one construction called "Locked Breech" and another known as "Delayed Blowback". Several actions are present on second group and "Gas Delayed is one of them with a well known member of HK P7. Though seeming rather simple as compared to locked breech samples, this working system needs precise workmanship and some additional measures for positive extraction for charged empty shell since very high pressure is still existing at initial stage of breechbolt rearward travel starts causing case separation.We'll ignore the typos because it was written in a comment box. This commenter apparently knows a thing or two about guns. He (or she) brings up a couple of interesting points. Case extraction is the first one.
Walther CCP is a new member of this kind, but seemingly having no remedy for possible mentioned case separation. Besides, This pistol's main spring that is giving force for striker, does is not compressed against to the recoil spring similar of new trend striker guns like Glock, but gets compressed against to a hook shaped post provided at rear of frame on which the key part of field stripping process weared. The pistol, therefore, is cocked during the last stage of breechbolt backward travel and, since this construction precludes the necessity of using costy frame and slide counterfitting rails, it is a cheap manufacturing method of inexpensive striker guns like HiPoint.
I'm thinking the problem of "case separation" happens when the breech bolt, with it's embedded case extraction hook, starts moving away from the breech too soon. The extraction hook is pulling on the shell, but the pressure inside the chamber is pressing the walls of the shell against the inside surface of the breech with such force that the shell walls cannot slide, and so the extraction hook rips the base of the shell from the body. Not good. This video about the HK P7 (Heckler & Koch P7) has a bit (just after the one minute mark) about what HK has done to alleviate this problem.
In designing a "gas delayed blowback" operated pistol, one would need to carefully consider all of the operating elements:
- the size of the powder charge,
- the position, diameter and length of the gas port,
- the diameter of the piston,
- the mass of the breech block, and
- the strength of the main recoil spring.
The second part, about the striker (firing pin?), I'm not too clear about. I think the complaint is that the part that holds the firing pin in the cocked position is prone to wear. If you are someone who puts a hundred rounds through your gun every week, week in, week out, then, yes, this could be a problem. But if you are burning through that much ammo I think you could probably afford to replace this "hook shaped post" occasionally.
If you are running a hundred rounds through this gun when you go to the range then you are liable to run into another problem long before you have worn out the hook, as this video about the HK P7 (same one as mentioned earlier) tells us just after the 2:25 mark.
7 comments:
Case separation occurs when the
thin side walls of case remain unsupported at instant of high pressure of burned powder charge being existing. On locked breech guns the main reason is uncorrect headspace, but blowback or delayed blowback guns, there are other causes and one of them is case sticking inside the chamber while the backside remaining away the breechblock support by cause of its free rearward travel via gained mmomentum. Longitidunal chamber grooves are cut for the case to float thereinside without sticking. On correctly cut, clean
lined chambers, the extractor hook
works only to take out the live rounds from the barrel. The force driving the empty case out is the
pressure inside the barrel, and not the extractor. But irregular chamber walls and fouling through the repeated fire may cause to stop and stick the empty case for a time to exhaust the remained gas pressure while the bigger mass of breechbolt going on its rearward travel via gained momentum and the extractor hook, if strong enough the retain its hold, takes the empty case back from the stuck position.
Regarding the "Hook shaped post", it is the non-moving upright thing standing at rear of the handle frame on which the back guide of striker spring seats as
keeping the whole impact elements inside the longitudinal tunnel cut at rear of the breechbolt. Since the thickness of this back guide is bigger than the hook shaped post, it remains the whoole breecblock over the frame at back and since the stationary barrel keeping the frontside of breechbolt being correctly fit over the frame, there is no need for longitudinal grooves for breechbolt to move back and forth over the receiver and this greatly reduces the manufacturing costs. But this construction needs the backward of striker tunnel being slidably plugged by a stationary post(Hook shaped one) and can not be used by the kinds with plugs mounted on the breechbolt like Glock, Walther or SW, and it also causes the main spring( The power source for impact element) to be compressed against to the this post and therefore the guns carrying such an action will be cocked at last stage of breechbolt rearward travel and not its forward voyage against to the recoil spring like current striker firers.
Thank you for clarifying this.
HKP7 and HK91 why the fluted chambers
HK says it's to "aid extraction", but it's not true. It it retard the opening of the action.
HK has videos out there showing the P7 reliably ejecting cases without an ejector at all, and claims it is due to the chamber flutes.
The truth is: Any semi-auto gun will cycle reliably without the extractor. The case PUSHES on the bolt, the extractor doesn't PULL it. Some guns don't even have extractors, like the Beretta tilt-barrel pistols including the model 21 .22lr, and the Tomcat .32. And the open-bolt .22 rifles like the Gevarm and the Voere - no extractor.
The challenge is to RETARD the recoil of the empty case from opening the action too soon. Short of locking the bolt/slide to the barrel, there are a number of ways to do this. The simplest is inertia, just have the bolt heavy enough, so that by the time the recoil of the case overcomes the inertia, the bullet has left the barrel. However if you don't want that much weight in your gun, you can use a combination of inertia, and a fluted/grooved chamber. There have been handguns sold that rely on deforming the case into a grooved ring in the chamber to delay the opening of the bolt. The Seecamp pistol is an example;
"chamber-ring delayed, in which the fired case expands to seal the chamber walls and delay extraction--the Seecamp pistol operates in this manner;"
http://www.thefreelibrary.com/If+it+...d.-a0197482929
And this is what the HKP7 does. They put flutes in the chamber from where the bullet leaves back about 1/2 the length of the case. The ring formed where the flutes end provides the same effect as the ring in the chamber if the Seecamp. The case deforms into the groves and straightening out the deformations as they pass over the REAR end of the grooves, provides resistance to rearward movement
With the HKP7 the action is is partially case-deformation retarded, and partially gas retarded.
And the HK91 rifle works the similarly. The groves do not extend to the rear of the chamber. Look at this picture: http://www.weaponeer.net/forum/uploa...mber_halfs.jpg
The HK91 action is partially case-deformation retarded, and partially roller retarded
With the P7 there is a short time delay (= about 1/2" in travel of the bullet) between when the round is fired and when the bullet is far enough down the barrel to feed gas into the hole to operate the gas-delay piston. But that would be plenty of time for the action to open and render the gas-delay system usless. So to cover the first 1/2" of bullet travel, HK cut out a fluted ring in the first 1/2" of their chambers in their gas delayed pistols.
Then for the P7 they released the ridiculous lie about it was done to allow the gun to operate without an extractor! And for the HK91 they released the lie that the flutes were to stop the extractor ripping the base of the case off! Extractors never pull unless you are hand-cycling the action.
That's why HK P7s are ammo-sensitive. This is what happens with P7s when you use cases with the wrong deformation metalurgy:
http://chris.cc/p7m13.htm
[[The Mystery of the HK P7M13 and the COR®BON Ammo..
Loaded up some COR®BON 115 gr., fired about ten times and the last round did not extract from the chamber. ]]
Operation depends on the material the case is made of. Seecamp is honest enough to say their pistols will only work reliably with one specific brand of ammo - winchester silvertop. They have coordinated the depth of their chamber-groves to match predictable deformation.
The HK91 is less ammo sensitive than the P7 because it is less dependent on case-deformation retardation, and more more dependent on its other method of retardation (roller retardation).
Quoted from - http://thefiringline.com/forums/showthread.php?t=438320
Simply, if the longitidunal grooves extend beyond the chamber shoulder, it is for ease of extraction, and if they remain behind the chamber shoulder, it is for delaying the opening speed of breechbolt. On the first kind, the gas pressure has a clear way to enter and create an equal force against to the gas force inside the case, as making it floated, and on second kind, gas pressure is effective only inside the case and free to swell the side walls inside the grooves as creating a delaying effect for breechbolt opening. However with a combination of unconnected flutes both extending beyond the chamber shoulder and remaining behind it, it would be possible both to create an ease for extraction and retarding the breechbolt opening which its function seeming rather questionable. What HK advertisers suppose, should be, the common function of extractors being solely for fluted chamber guns.
TYPO: "HK has videos out there showing the P7 reliably ejecting cases without an ejector at all.."
SHOULD READ
"HK has videos out there showing the P7 reliably ejecting cases without an extractor at all.."
Anon wrote: "if the longitidunal grooves extend beyond the chamber shoulder, it is for ease of extraction, and if they remain behind the chamber shoulder, it is for delaying the opening speed of breechbolt."
SS replies: I agree with the 2nd part, and the HKP7 is an example of "longitidunal grooves remain behind the chamber shoulder"
https://lh5.googleusercontent.com/-vn6faxwITb8/UEfdVC4REoI/AAAAAAAADD4/ZWrsmf101kk/s576/P1000325.jpg
The G3 rifle is another example
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Fluting/x51flutes101010005.jpg
I can't think of an example of the 1st part "longitidunal grooves extend beyond the chamber shoulder". This would allow very hot gas at 35K psi(9mm) or 60K psi(.308) to vent immediately into the action of the gun.
Anon wrote: "if the longitidunal grooves extend beyond the chamber shoulder, it is for ease of extraction, and if they remain behind the chamber shoulder, it is for delaying the opening speed of breechbolt."
I believe they are referring to chamber/breech face shoulder rather then the neck/barrel shoulder(for clarification?).
If the flutes were to extend beyond both then indeed it would vent hot gas into the action of the gun. If they extended beyond the cartridge in only one direction I believe it would aid extraction. Though affecting the chamber/breech face shoulder would be most effective in either effort. The other would require experimentation.
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