Causes of hard bolt lift?

[44man]

Actually, it's the other way around. The purpose of the flutes is to allow combustion gasses to float the case to facilitated extraction while under high pressure. Without those flutes the cases have difficulty extracting.

Too high case to chamber wall grip is not desirable and can cause hard bolt lift. It can also increase shock loading to the bolt face (when the gripped case suddenly slides back under high pressure as opposed to settling back at lower pressure). Some folks polish their rifle chambers by spinning a fired case with Flitz on it, using a drill. I can't comment on that as I have never done it but from what I can remember it stops case head separation and/or case elongation. One person has stated that he found polishing his rifle chamber resulted in stiff bolt lift which is opposite to what I am saying. He says he leaves his chambers as reamed and does not get stiff bolt lift. So I am giving you contradictory views. I have never had stiff bolt lift from low case grip but have from the case expanding into rust pits in the neck. I also don't load to 60,000 psi.

I'm of the opinion that consistent case wall grip is important for accuracy and that could be what is being achieved on target type rifles.

Never want a high polish in the chamber. But rough tool marks are not too good either.
You are wrong about the fluted chamber, it increases area to hold the brass long enough to reduce pressures before extraction. Flutes reduce head pressure and slow extraction. They are full auto guns mostly that would beat themselves to destruction. It was a fix to increase rate of fire without making springs stronger.

[303Guy]

I stand corrected then. I did get the information that it was a fix to solve the problem of the extractor tearing through the rims. Well, we live and learn. I was also wrong about never having stiff bolt lift with too smooth a chamber. I found an entry in which I did have stiff bolt lift with a lightly lubed case. I entered that pressure was too high and that there was cratering on the primer. OK, so I don't deliberately load to 60,000 psi! And with cast too! I think the max allowable for the Brit is 50,000 psi (43~45,000 CUP)

My 22 hornet has a rough chamber and that tears the cases in short time so I lube the cases well and that overcomes that problem. They do not have a neck to headspace on so I headspace them on the case mouth.

[Larry Gibson]

303Guy is correct; "Actually, it's the other way around. The purpose of the flutes is to allow combustion gasses to float the case to facilitated extraction while under high pressure. Without those flutes the cases have difficulty extracting."

The fluted chamber was developed by German engineers to provide reliable functioning with full power NATO spec 7.62 ammunition in the CETME rifle. Simple research the history of that rifle and you'll find the reason. Chamber fluting was carried over in the H&K series of rifles and a few others.

Larry Gibson

[44man]

303Guy is correct; "Actually, it's the other way around. The purpose of the flutes is to allow combustion gasses to float the case to facilitated extraction while under high pressure. Without those flutes the cases have difficulty extracting."

The fluted chamber was developed by German engineers to provide reliable functioning with full power NATO spec 7.62 ammunition in the CETME rifle. Simple research the history of that rifle and you'll find the reason. Chamber fluting was carried over in the H&K series of rifles and a few others.

Larry Gibson

OK, I might be wrong with what I read about them. But how do gasses "float" a case? Only thing I can see is to dissipate chamber pressure by enlarging the expansion area.
Remember the .22 Jet in the S&W revolver? Needed to lube brass or they stuck. Why have billions of full autos been made without flutes.
Last I read was for flutes to retard bolt open just enough.
Give me a link.

[WALLNUTT]

How would chamber flutes increase area of contact?

[fouronesix]

Don't dispair 303Guy- yes you are mostly right. This same nonsense of a conspiracy about H&K hiding the truth about the fluted chamber has been circulating the net for at least a couple of years. But there are those on the web who love and live for conspiracies, black helicopters and men in black. Those are the same ones who always seem to have a secret truth.

[44man]

How would chamber flutes increase area of contact?

Expand into flutes that increases brass contact with chambers. Should double brass contact.
I might be right about more resistance to head pressure.
I have not come to terms of "float".

[Harter66]

The fluted chambers were intended to allow the rifles to run longer cooler and dirtier . The chamber fluting actually reduces wall contact area. And increases surface area to be heated. Most of them start about .1 from the case mouth . The H&K 92 was intended to run in the desert w/lots of sand but mud also . It was determined tha t an overall tight therefore accurate chamber could be had and still feed dirty , rusted ammo. Kind of like the sloppy AK and SKS.

[44man]

Beware of Commercial .308 and Fluted Chambers

Posted April 30, 2013 in News, Other Gear & Gadgets, Rifles by Alex C. with 84 Comments

1810
0*0
*1 7

My good friend CJ is a real whiz at building H&K roller locked stuff. Back in the day when G3 parts kits were affordable and flowed into the United States like water anyone could build one for a few hundred bucks. The problem however (aside from relative build difficulty) was that a true G3 spec chamber does not like commercial .308 Winchester ammunition. G3 rifles have an internally fluted barrel. This aides in extraction and prevents the possibility of an extractor breaking, and a shell sticking. The gas from the discharge is forced back and around the spent shell blowing it out of the breech. So, in the event an extractor breaks, or some ammunition failure, you will definitely get the spent case out of the weapon. With no extractor at all it will eject a round, or at worse cause a partial ejection which requires you to pull the cocking handle and drop the round out. The problem with this is it mangles brass. CJ found this out the hard way:

What you see here is what can happen. This was commercial .308 fired in a properly built G3; It is very dangerous and can kill you. You must use 7.62×51 NATO if you have a true G3 spec barrel. As you can see, the top of that round has the aforementioned flute marks – that’s what a spent shell looks like – it gets ruined. Now, if you notice… that’s only 1/3 of a shell, the rest of it was ripped off. Since commercial .308 is much thinner cased, when the round discharges the more pliable case expands and actually sticks in the flutes, and given the power of the round, the extractor literally rips the back of the case off, leaving the front of the shell stuck in the barrel. The next round was cycled in with such force, it actually slid itself through the remaining case neck. Luckily CJ noticed the rifle wasn’t in full battery and didn’t fire it (that would have been catastrophic).
H&K 91 rifles had a much looser chamber to allow the firing of .308 ammunition, and modern manufacturers of G3 pattern rifles seem to have adopted a similar chamber. Just beware of what can happen and be safe!

- See more at: http://www.thefirearmblog.com/blog/2....J3SO42Fi.dpuf
A few things.
Beware of Commercial .308 and Fluted Chambers

Posted April 30, 2013 in News, Other Gear & Gadgets, Rifles by Alex C. with 84 Comments

1810
0*0
*1 7

My good friend CJ is a real whiz at building H&K roller locked stuff. Back in the day when G3 parts kits were affordable and flowed into the United States like water anyone could build one for a few hundred bucks. The problem however (aside from relative build difficulty) was that a true G3 spec chamber does not like commercial .308 Winchester ammunition. G3 rifles have an internally fluted barrel. This aides in extraction and prevents the possibility of an extractor breaking, and a shell sticking. The gas from the discharge is forced back and around the spent shell blowing it out of the breech. So, in the event an extractor breaks, or some ammunition failure, you will definitely get the spent case out of the weapon. With no extractor at all it will eject a round, or at worse cause a partial ejection which requires you to pull the cocking handle and drop the round out. The problem with this is it mangles brass. CJ found this out the hard way:

What you see here is what can happen. This was commercial .308 fired in a properly built G3; It is very dangerous and can kill you. You must use 7.62×51 NATO if you have a true G3 spec barrel. As you can see, the top of that round has the aforementioned flute marks – that’s what a spent shell looks like – it gets ruined. Now, if you notice… that’s only 1/3 of a shell, the rest of it was ripped off. Since commercial .308 is much thinner cased, when the round discharges the more pliable case expands and actually sticks in the flutes, and given the power of the round, the extractor literally rips the back of the case off, leaving the front of the shell stuck in the barrel. The next round was cycled in with such force, it actually slid itself through the remaining case neck. Luckily CJ noticed the rifle wasn’t in full battery and didn’t fire it (that would have been catastrophic).
H&K 91 rifles had a much looser chamber to allow the firing of .308 ammunition, and modern manufacturers of G3 pattern rifles seem to have adopted a similar chamber. Just beware of what can happen and be safe!

- See more at: http://www.thefirearmblog.com/blog/2....J3SO42Fi.dpuf
Beware of Commercial .308 and Fluted Chambers

Posted April 30, 2013 in News, Other Gear & Gadgets, Rifles by Alex C. with 84 Comments

1810
0*0
*1 7

My good friend CJ is a real whiz at building H&K roller locked stuff. Back in the day when G3 parts kits were affordable and flowed into the United States like water anyone could build one for a few hundred bucks. The problem however (aside from relative build difficulty) was that a true G3 spec chamber does not like commercial .308 Winchester ammunition. G3 rifles have an internally fluted barrel. This aides in extraction and prevents the possibility of an extractor breaking, and a shell sticking. The gas from the discharge is forced back and around the spent shell blowing it out of the breech. So, in the event an extractor breaks, or some ammunition failure, you will definitely get the spent case out of the weapon. With no extractor at all it will eject a round, or at worse cause a partial ejection which requires you to pull the cocking handle and drop the round out. The problem with this is it mangles brass. CJ found this out the hard way:

What you see here is what can happen. This was commercial .308 fired in a properly built G3; It is very dangerous and can kill you. You must use 7.62×51 NATO if you have a true G3 spec barrel. As you can see, the top of that round has the aforementioned flute marks – that’s what a spent shell looks like – it gets ruined. Now, if you notice… that’s only 1/3 of a shell, the rest of it was ripped off. Since commercial .308 is much thinner cased, when the round discharges the more pliable case expands and actually sticks in the flutes, and given the power of the round, the extractor literally rips the back of the case off, leaving the front of the shell stuck in the barrel. The next round was cycled in with such force, it actually slid itself through the remaining case neck. Luckily CJ noticed the rifle wasn’t in full battery and didn’t fire it (that would have been catastrophic).
H&K 91 rifles had a much looser chamber to allow the firing of .308 ammunition, and modern manufacturers of G3 pattern rifles seem to have adopted a similar chamber. Just beware of what can happen and be safe!

- See more at: http://www.thefirearmblog.com/blog/2....J3SO42Fi.dpuf

[44man]

Sorry things got tripled.

[44man]

Another one.

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).

[44man]

Another Back in the 70's there were a lot of articles written about the Heckler and Koch rifles with the fluted chambers. Instead of conventional square locking lugs they used rollers in the bolt to lock it and they incorporated the flutes in the chamber to help delay the bolt from moving rearward until pressures were down to the proper amount. It is a well engineered system and is still used in their .223 and .308 rifles. Hk 92 an Hk 93's ? There were several articles about reloading the ammo and it was found that there was no problem with reloading the brass. It was just unsightly seeing the slight grooves remaining in the brass after resizing. Definitely tumble the brass! Inspect the brass for cracks etc. the same as you would normally do. If any of you are interested in a "battle" rifle that is accurate enough for varmints, buy an HK.!!!

Bob In St Louis

[44man]

Yes, some say gas goes outside the brass to the bolt to aid extraction,adding to bolt thrust, Float. Yet brass sticking at the back of grooves is still to retard head pressures. How is it explained?

[MBTcustom]

You learn something new every day. I had heard of the fluted chambers, but had no earthly idea of why they would do that. Very interesting.
Thanks 44man.

[shooterbob]

Could it possibly be leading a bit and now the larger boolits are causing a pressure spike?