I picked up an AMT .22 mag auto pistol that has a chamber with holes in it, instead of flutes... there are 6 of them about .015 diameter... not exactly flutes, but no idea what good they do.... since AMT is out of business, wonder what the engineers were thinking??.... I've also picked up .308 Winchester brass on the range that have witness marks on them, looks like they were shot in a chamber that had grooves in it??... whats the benefits???

The .308 brass is most likely from an H&K 91. I was told that this was done to ensure positive chambering and extraction in a battle weapon.
However I do not know about the AMT.

Not really. HK's bolts lock up with (retracting) rollers instead of the usual turning bolt head. To avoid early unlocking, the chamber is fluted to increase its grip on the fired case and retard opening. The system works as experienced by HK's defunct (but brilliantly executed and expensive) P 7 pistol which was a 9 Para using a simple blowback with no other lock up than the fluted chamber. The only gripe this handloader has against fluted chambers is that they shorten case life due to the flutes impressed (in reverse) in the case body.

You got it backwards; chambers in CETMES and HKs are fluted so the brass will "float" on a cushion of gas to make extraction easier. That is also why the actions get so dirty from all the gas that gets blown into it. The roller bolts are not really locked; they only delay the opening, which is more of a blowback system. Quite fast and violent opening so they fluted the chamber to make sure the brass would NOT stick. I have reloaded a lot of brass I fired in a SIG AMT with fluted chamber and it did not shorten the case life. It just leaves striations in the brass but does not hurt it.
AMT? Only reason for a ported chamber is to release gas into a suppressor.

DPCD +1..except that I have never reloaded such striated cases but I knew of some who did.

FWIW I think that H & K's sporting self-loading rifle...was it the 770 (?)...was available, I think, with an without the fluted chamber as an option choice.

Yes, I remember that one but I always assumed it had flutes as well. I don't think the action would work without the flutes.

i messed around with a h&k some time back. i was very dissatisfied with the accuracy and tried to get h&k to put a psg barrrel on the rifle, but they wouldn't so i tried to rebarrel the thing with a plain one. without the flutes it wouldn't function.but if i lubed the cases it would,but the fired cases had blown out shoulders from ejecting to soon,but if i used hornady one shot on them it would function just fine. finally sold it to a guy that had a edm machine don't know what the final result was. but reloading the fluted cases provided no problems except that they were quite dirty

Interesting. With good barrels, these things are very accurate as there are basically no moving parts like a piston, etc. My SIG was sub moa. The triggers on HKS are very heavy, which is for a German Army spec drop test.

quote:

Originally posted by Andre Mertens:
Not really. HK's bolts lock up with (retracting) rollers instead of the usual turning bolt head. To avoid early unlocking, the chamber is fluted to increase its grip on the fired case and retard opening. The system works as experienced by HK's defunct (but brilliantly executed and expensive) P 7 pistol which was a 9 Para using a simple blowback with no other lock up than the fluted chamber. The only gripe this handloader has against fluted chambers is that they shorten case life due to the flutes impressed (in reverse) in the case body.

H&K P7 was not a straight blowback - it was a gas-delayed (or retarded) blowback system, and was locked (for a small time) by the the gas going through a port from the front of the chamber IIRC.

Anyway, it didn't delay it by much and the ejection was fairly robust ....

I know it has been a while since this question was asked, but there's a fairly detailed discussion of the Automag II's chamber here:

http://www.amtguns.info/automa...amber_topic1264.html

Basically, the designer (Larry Grossman) used an inserted bushing with drilled holes to do the same basic thing as the CETME/HK fluted chamber, to allow the thin walled rimfire brass to extract without blowing the case head off. The .22 Magnum was never intended for use in an autoloader, and the thin rimfire head wouldn't reliably contain pressure as the bolt moved back. The gas holes let the case slide back when it would ordinarily have been locked to the chamber, letting the case head use the bolt face for support.

quote:

Originally posted by Bren7X64:

quote:

Originally posted by Andre Mertens:
Not really. HK's bolts lock up with (retracting) rollers instead of the usual turning bolt head. To avoid early unlocking, the chamber is fluted to increase its grip on the fired case and retard opening. The system works as experienced by HK's defunct (but brilliantly executed and expensive) P 7 pistol which was a 9 Para using a simple blowback with no other lock up than the fluted chamber. The only gripe this handloader has against fluted chambers is that they shorten case life due to the flutes impressed (in reverse) in the case body.

H&K P7 was not a straight blowback - it was a gas-delayed (or retarded) blowback system, and was locked (for a small time) by the the gas going through a port from the front of the chamber IIRC.

Anyway, it didn't delay it by much and the ejection was fairly robust ....

Exact, with a slightly premature ejection just before pressure rteachesits lower point.


Roller-locked H&K pistols are the VP 70, VP 70Z and P 9

quote:

Originally posted by Andre Mertens:
Not really. HK's bolts lock up with (retracting) rollers instead of the usual turning bolt head. To avoid early unlocking, the chamber is fluted to increase its grip on the fired case and retard opening. The system works as experienced by HK's defunct (but brilliantly executed and expensive) P 7 pistol which was a 9 Para using a simple blowback with no other lock up than the fluted chamber. The only gripe this handloader has against fluted chambers is that they shorten case life due to the flutes impressed (in reverse) in the case body.

The flutes DECREASE the grip on case with the assistance of gasses flowing between case and walls of the chamber. without tyhem, there is head separation.

Yes, the bolt head starts to move at max pressure . That will tear off the case head --so the flutes are there to prevent that high pressure .The P7 cases have mostly discoloration instead of actual flutes . P7, one of the nicest pistols I know .Mine are not " defunct" !
The VP 70 is a plain blowback , not locked or delayed blowback !! The grooves are twice the normal depth so you loose about 150 fps velocity .That way you can easily pull back the slide with the lighter spring. A terrible design !

The "holes" in The AMT 22 Mag were designed to retard case extraction, ie so the action would not open too soon, at to high a pressure.

On the H&K guns dcpd is basically correct. The flutes are designed to keep the brass from sticking too "tight" in the chamber. The flutes allow the pressure of the gas to "float" the case in the chamber to AID extraction to the "roller locked" action, that is not actually locked at all, just delayed.

I have extensive firing experience with H&K's in 9mm, and 45 ACP in handguns, and 9mm, 223/5.56, and 308/7.62mm in long guns.

I have reloaded several thousands of fired cases from these guns. Case life is actually longer in the 223/5.56 and 308/7.62 H&K's than other "conventional" semiauto's. Mainly due to the fact that in conventional semiautos the bolt "pulls" the case out of the chamber stretching the web, where as in the H&K system, the case "pushes" the bolt back and the web is not stretched. I stopped testing brass life after 11 firings in an H&K 91...

Also the H&K sporting rifles like the 660, SL6 and the 770, SL7 all had fluted chambers.

As to accuracy, the H&K long guns have been some of the most accurate rifles I have ever fired.

On the H&K 33/93, and the G3/91 the barrels are free floating. Even after several magazines there is no zero shift.

I have killed a lot of deer, a few antelope and several pigs with an H&K 91.

IF the BAD DAYS ever do come, and I could only have ONE rifle, I would be an H&K 91...