View Full Version : fluted chamber?
Does anyone make an AR barrel with a fluted chamber?
Larue's XTRAN chamber has flutes along the case body. Used in the OBR. The barrel is a Lothar Walther, but I don't know if Larue is finishing the chamber or if LW is.
Haven't seen anyone else doing it.
Thanks. I'd like to build one up...
KrampusArms
09-17-12, 22:26
Whats the purpose of fluting a chamber? I know the G3 rifle had this to aid in extraction? Are there any other benefits?
Fluted chambers are pointless in an AR-15. The main purpose is to channel to gas back to the surface of the case for a little push to aid in cycling in roller locked weapons.
Brass that has been run through a fluted chamber generally can't be reloaded.
KrampusArms
09-17-12, 23:13
Understood. I can imagine this causing trouble in an AR15 rifle, now that im thinking about it.
sinlessorrow
09-17-12, 23:29
XTRAXN™ is a proprietary chamber feature added to reduce frictional forces caused by pressure-expanded cartridge cases bearing against chamber walls. Facilitates reliable extraction through a wide range of temperature / chamber pressure extremes. XTRAXN™ extends extractor life, while having no effect on the firearm's accuracy. All this, and it dovetails well with the OBR's world-famous accuracy.
http://img194.imageshack.us/img194/7307/58131076.jpg
http://img.photobucket.com/albums/v145/AUSTINWFT/LT%20Post/OBR%20XTRAXN%20Reload/IMG_0297.jpg
http://img.photobucket.com/albums/v145/AUSTINWFT/LT%20Post/OBR%20XTRAXN%20Reload/IMG_0302.jpg
everyusernametaken
09-17-12, 23:31
What's the story on that?
DeltaSierra
09-17-12, 23:35
Come on...
You really have to quote all the photos? Seriously?
sinlessorrow
09-17-12, 23:38
What's the story on that?
That is the xtraxn chamber from Larue, and what it does to brass.
everyusernametaken
09-18-12, 00:04
Come on...
You really have to quote all the photos? Seriously?
Edited it. Is that better?
DeltaSierra
09-18-12, 00:11
Much better.
Thank you.
:)
9mm brass from a MP5 looks the same. ;)
XTRAXN™ is a proprietary chamber feature added to reduce frictional forces caused by pressure-expanded cartridge cases bearing against chamber walls. Facilitates reliable extraction through a wide range of temperature / chamber pressure extremes. XTRAXN™ extends extractor life, while having no effect on the firearm's accuracy. All this, and it dovetails well with the OBR's world-famous accuracy.
P.T. Barnum was right. :blink:
My God, that's a line of salesman horse shit.
Not gonna touch what the flutes are supposed to do ,but what makes this brass unable to be reloaded.
Nothing. I've reloaded plenty of brass out of roller lockers. The M1A/M14 is harder on brass. The flutes don't hurt anything...but without a port buffer, the big honking dent in the body of the case is what can jack up brass from a roller locker.
The Sierra reloading manual used to carry a warning about reloading brass that had been through a fluted chamber. They recommended using a FL sizing die. My experience has shown that FL dies work the brass to hard and you will be lucky to get 2 reloads out of it before it cracks.
Now, I don't work for Magpul but I did stay at the Holiday Inn last night...:dirol:
Not gonna touch what the flutes are supposed to do ,but what makes this brass unable to be reloaded.
You can do a lot of things in reloading that aren't worth the hastle.... including reload steel cases.
When I find fluted brass, it goes straight into the recycler. Usually the gun it's been fired in will have destroyed the rim anyway. Fluted brass is generally completely fuXored up and not worth the hastle.
The Sierra reloading manual used to carry a warning about reloading brass that had been through a fluted chamber. They recommended using a FL sizing die. My experience has shown that FL dies work the brass to hard and you will be lucky to get 2 reloads out of it before it cracks.
Now, I don't work for Magpul but I did stay at the Holiday Inn last night...:dirol:
When the brass cracked were the cracks along the flutes or at the shoulder? I'm really just curious, not gonna have a weapon like this anytime soon.
Ned Christiansen
09-18-12, 10:21
I had a boutique manufacturer ask me to get some chambers fluted a couple years ago (AR15). I told him that for the expense of it, I didn't think it'd be worth it, and that I was concerned that being a rotating bolt design, it might impede function more than anything else. The systems that were originally designed with a fluted chamber to aid extraction-- the HK's, CETMEs, StG 57, the FAMAS-- none of them have a rotating bolt.
Question: when an AR unlocks by rotating the bolt, does the case turn with it or does the bolt turn on the case? My observation has been that it does whatever it feels like-- turns, doesn't turn, turns part-way.
I can imagine that with flutes, the fired case doesn't turn in the chamber as the bolt unlocks. But I'd say it looks like LaRue has proven that this is not a concern. Not sure I'm sold on it as an improvement, but on the other hand I can't feature an outfit of their standing offering this without having proven that it helps at least on a theoretical level. I just can't see them offering something that is not proven to at the very least, cause no harm.
It it just me or is there a very, very slight helix to the "flute prints" on the cases?
It it just me or is there a very, very slight helix to the "flute prints" on the cases?
Looks like that to me too. And the brass isn't nearly as damaged as you see on a roller locker concoction.
Not helical, just angled. I think straight lines on the surface of the brass is an optical illusion.
P.T. Barnum was right. :blink:
My God, that's a line of salesman horse shit.
No kidding.
Ned Christiansen
09-18-12, 11:45
I don't see anything oin their site about it-- search and all. Nor about the adjustable gas block mentioned on the OBR's.
The Sierra reloading manual used to carry a warning about reloading brass that had been through a fluted chamber. They recommended using a FL sizing die. My experience has shown that FL dies work the brass to hard and you will be lucky to get 2 reloads out of it before it cracks.
Now, I don't work for Magpul but I did stay at the Holiday Inn last night...:dirol:
Well, yes you use a FL die, but you use a FL die for any S/A anyway. I've never even had to use small base dies on the brass. And, you can get far more than 2 loadings, although with a roller locker, it usually flings it into something and makes it ugly long before any cracks appear.
I FL size everything, even bolt guns. Brass life is fine, I just have to trim every few firings depending on the cartridge and chamber. In reality, if I have to trim a second time, I pitch the brass.
And, I can guarantee you that working at Magpul has ABSOLUTELY no bearing on a discussion of roller locker flutes and reloading.
Back in the day I used to handload bear protection rounds for my HK91 using 180 grain bullets. No issues at all getting 4 to 5 firings from a piece of brass out of it.
Well, yes you use a FL die, but you use a FL die for any S/A anyway. I've never even had to use small base dies on the brass. And, you can get far more than 2 loadings, although with a roller locker, it usually flings it into something and makes it ugly long before any cracks appear.
I was thinking the same thing. I used to reload the brass from my Garand when I owned it probably more than 5 times and they are notoriously hard on brass, especially on the case mouth and on the head from it's authoritative extraction.
BufordTJustice
09-18-12, 20:07
Not helical, just angled. I think straight lines on the surface of the brass is an optical illusion.
Yeah, they appear angled (i.e. not perpendicular to the bore).
Question: when an AR unlocks by rotating the bolt, does the case turn with it or does the bolt turn on the case? My observation has been that it does whatever it feels like-- turns, doesn't turn, turns part-way.
It it just me or is there a very, very slight helix to the "flute prints" on the cases?
Good points. I think I see a slight helix in the fouling on those cases. Why it's there I don't know.
I can't recall ever seeing any marks in either the fouling on the surface of, or on the actual fired brass of an AR that would lead me to believe that the cartridge case rotates on extraction.
Now for the rest of the story. Back in the big bad 80's I was stationed in W. Germany. The Germans had a novel way of dealing with a G3 that wouldn't reliably extract due to excess fouling. Now I gotta say, it takes a lot of fouling to choke a G3, but it can happen. Rather than try to do a quick field cleaning they would lightly coat a cartridge with petrolium jelly and fire it. The fouling in the flutes would adhere to the jelly and the rifle would self clean a bit to the point of reliability.
As otheres have already pointed out, the flutes in the G3 are necessary due to the delayed blowback system. If the flutes fill up with crud, the rifle stops reliably extracting. Given that the AR doesn't utilize a blowback action in center fire rifle calibers, I wonder how many rounds it would take to start having extraction issues with a fluted chamber?
Heavy Metal
09-20-12, 19:51
Notice the fact with the Larue Chamber flutes there are no flutes on the case shoulder or scorch marks from carbon.
It is an entirely different beast from the H&K Flutes, apples and oranges. The Larue flutes have no fluidic connection to the barrel as the H&K flutes do.
The purposes of the H&K Flutes is to 'float' the case as the bolt unlocks.
Delayed Blow-Back rifles commence opening the bolt much sooner than a rotating bolt design and the residual chamber pressure is still very high by comparison. Without the flutes, the case will still be sufficiently obtruded into the chamber walls to allow the still high residual pressure to blow the head off the case body and leave a seperated casing in the chamber, casuing an obviously nasty stoppage.
The H&K flutes are a solution ot a problem unique to the delayed bolwback system H&K uses and copied by the French in their various small arms that use a similar in concept but different in execution delayed blowback system.
That is the reason for the H&K Flutes. They allow gas to leak from the barrel to the chamber walls. A clever solution to what must have been a vexing problem at the time.
In an AR, all the H&K type flutes would likely accomplish is to increase bolt thrust and by the time the bolt was unlocked, the residual pressure on the case walls would be low enough to be of no relative use anyways. Plus they would dump a shit-ton of additional soot into the bolt face and reciever extension area.
In an AR, all the H&K type flutes would likely accomplish is to increase bolt thrust and by the time the bolt was unlocked, the residual pressure on the case walls would be low enough to be of no relative use anyways. Plus they would dump a shit-ton of additional soot into the bolt face and reciever extension area.
I agree that it's LaRetarded, but the fanboys will only riot and loot. So screw it. :blink:
Heavy Metal
09-20-12, 20:26
Notice the brass photos, no marks on the shoulder and no soot. They are not fluidically connected to the bore in any way!
They are only a bit cosmetically similar and functionally not at all similar.
Ned Christiansen
09-20-12, 22:45
I guess the idea here was to simply reduce the contact area and, so, the "potentially stuck" area.
Edited it. Is that better?
Only from the standpoint of having saved a staff member the trouble.
It'll only be "better" when members manage to not quote posts immediately above their own (seriously, who the f**k else would you be asking/commenting, without needing to take the time to specify...? It's dumb.)
Or ALL of the photos in any given post, when they only have a question/comment about ONE of them. That's somebody too lazy to highlight and delete; I understand it can be a positively Heraclean task to work a mouse and a keyboard, pobrecita.
I wonder, is this a real improvement, or just something that can add more cost to the rifle than it does to production that "looks cool"?
If it is the former and not the latter, why wouldn't LaRue release test data of whatever nature to support it?
...The purposes of the H&K Flutes is to 'float' the case as the bolt unlocks.
Delayed Blow-Back rifles commence opening the bolt much sooner than a rotating bolt design and the residual chamber pressure is still very high by comparison. Without the flutes, the case will still be sufficiently obtruded into the chamber walls to allow the still high residual pressure to blow the head off the case body and leave a seperated casing in the chamber, casuing an obviously nasty stoppage...
Actually, the flutes allow the brass to be "floated" during firing. The flutes in the HK allow pressure to be equalized inside and outside the case wall so it does not expand as much during peak pressure as it would in a standard chamber. This means the neck does not seal the chamber as it does in a normal chamber, but it seals down near the web.
The HK does not blow the head off the case without the flutes. Without the flutes, extraction is unreliable. Just ask anyone who bought a PTR91 with a Thompson barrel that had little to no fluting
The more I think about it, the more I agree with Heavy Metal's reply.
I mean... I can remember debating the idea of getting all the case lube off the brass so that the brass would grip the chamber like it's supposed to.
Modifiying the chamber so it decreased the brass grip to the chamber wall doesn't make sense at face value. Strikes me as a gimmick at best.
Either the case turns upon extraction, or the extractor rotates around the case-head. There is physically no other option. This rotation happens at a rate faster than the "rate" that these flutes are machined at. This is also a physically unavoidable fact, based on the picture in this thread, and the knowledge that unless your M4's bolt is to shear its lugs, or those of the barrel extension, it will not be extracting a casing UNLESS it rotates.
The question now is...does the extractor slide around the case-head, or does the entire casing rotate, or does both occur for optimal function/reliability?
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