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chamber fluting.

33K views 34 replies 20 participants last post by  scottinthegrove 
#1 ·
quick question for every/any1.... the aftermarket barrels availanle for builds....are the chambers fluted like the origional HK/Cetme ? In particular the JDL 20" heavy barrel. thanks
 
#3 ·
tron... hks ( i dont know it cetme do) and some clones also have there chamber fluted too. Where a traditional gas operated rifle requires obturation (the case expands inside the chamber to provide a seal so theres no blowback ) in the case of a delayed roller locking system the fluting internally of the chamber actually allow gas to be pushed rearward and assist in the re-cocking of the rifle. If youve ever fired a rifle that has a fluted barrel you will see that carbon has been deposited on the spent casing leaving lines going from top to bottom ( not very techincal i no ).

The reason why im asking is because Im in Ireland.... I unfortunatly cannot import a JDL 20" fluted barrel... I think for the price they are there a Steal and gladly pay 2-3 times what they quote for a barrel and trunnion..... anyway...

If the chamber isnt fluted I will go ahead and make 1 myself, which really in time and hassle of trying to impost a barrel blank is worth $2000 in sanity !
 
#4 ·
In the instance of the Vorgrimmler actions the chamber is fluted to aid in extraction and cycling. Fluting may also be on the outside of the barrels, which is supposed to be a compromise between weight and barrel diameter... some say will make the rifle more accurate, others have debunked this theory.

HTH.
 
#5 · (Edited)
What is fluting. Here's a picture and I'll try to explain, but will probably not be as helpful as I wanted to be.



That's a G3 cutaway (poor G3...). Toward the center of the picture you can see the rollers attached to the bolt system and how the firing pin sits inside. Keep on moving to the left and you see the cutaway of the chamber area where the cartridge goes (seats). Notice those grooves that run along the walls of the chamber? Those are the flutes. The flutes serve a very important role, as explained earlier in the thread, in the proper cycling of the weapon. That channeling of gas "back" through the flutes will leave "scorch" marks on the brass.

Some folks will tell you that brass with these flute marks is unsuitable for reloading. Some will tell you not worry about it. Since I have never had the patience for reloading (I may have to learn!), I never bothered with trying to use the stuff or forming my own opinion.

Here's a better picture of an MP5 cutaway:



You get a much better impression of the flutes as opposed to just the rifling.
 
#6 ·
I do reload my 5.56 and .308 brass from the H&K's. The flutes do actually leave physical impressions. I simply shoot the H&K impressed brass in H&K's and the non impressed in the others. .308's pretty much fail at the shoulder, fluting or not. The 5.56 will fail along the flutes, eventually, usually at the throat. They will split or crack, after about 4-5 reloads.

I had been told the flutes also make extraction easier, as the shell is not completely held in the chamber from expansion.
 
#7 ·
A good view of the fluting.... this is an AK barrel , by da way... some people know what going on here...






 
#19 ·
Nahhh, but I will agree to bring back a buncha beer coasters from any number of beer halls...:D:D They got a Hooters in Krautnikstan?
 
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#28 ·
Insomnia has crept in so I've decided to dig up a really old thread.

Sounds like flutes are a must here, so why then is it said that the MP5 really doesn't need flutes? Is it because 9mm doesn't have enough pressure to expand the case? What about .40 then?
 
#29 ·
I really don't know about 40 cal. No ones ever tried a non-fluted barrel in 40 to my knowledge. It has EVERYTHING to do with the fact the pistol cals do NOT have spring loaded locking levers holding the boltheads like the rifle cal guns do, I would imagine.

I'll axe my buddy Cooter if his SW-45 has a fluted chamber later this morning.

As for the insomnia, start quaffing Nyquil... :biggrin:
 
#31 ·
One of the interesting back ground information in "Full Circle - A Treatise on Roller Locking" was the use of chamber flutes to even out the extraction force between brass and steel cases (the brass expands easier into the flutes tends to even out the forces vs steels less expansion / contraction ratio ... or something like this, everyone needs to purchase the book ;-).
 
#32 · (Edited)
My limited understanding is that the absolute requirement for the flutes is the pressure inside the shell casing. Rifle calibers have much higher working pressures than pistol calibers. So a 9mm round has low enough pressure that the shell casing doesn't "adhere" to the chamber walls so hard that the extractor can't pull the shell along with the face of the bolt. Since the bolt in a roller locked gun isn't actually "locked", during the high pressure stage of the firing sequence, the shell casing is moving out of the chamber. The mechanical disadvantage of the bolt pushing against both the trunion and carrier, through the locking piece, slows the bolt from opening during the high pressure phase. Because the high pressure phase is so short, by the time the action over comes the mechanical disadvantage, the pressure has been reduced to a safe level for the action to be open.

Without chamber fluting, the higher pressures of rifle rounds would cause the shell casing to be pushed against the chamber walls so hard that the casing can not move back with the bolt. The bottom of the case will shear off with the base remaining on bolt face and the rest of the casing remain in the chamber. The fluting equalizing the pressure on the chamber side of the shell casing allows the rifle casing to slide out as the bolt moves back.

I'd imagine the fluting in the pistol caliber guns is to make the extractors and bolts last longer. It would seem to me that the extra strain of the extractor having to pull the shell casing out under pressure would put more strain on the extractor. This in turn would put more strain on the bolt where the extractor is splined into the bolt, causing more wear.

Scott
 
#33 ·
Yep yep... ok, got all that and it's understood. But the million dollar question is does the 9mm and .40 really need chamber flutes? The easy answer is "yes" because factory guns have them, but I am looking for the practical answer. Anyone with first hand experience in either/both calibers?
 
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#35 ·
The difference is does the chamber "need" to be fluted or "should" the chamber be fluted? As many have posted Special Weapons early guns didn't have fluted chambers and they functioned. But the extra strain on the extractor/bolt pulling the case that is being pushed against the chamber wall during the high pressure phase of the cycle would make for more wear. I'm sure HK during the original R&D tried fluted and unfluted chambers. With as many pistol caliber roller locked barrels as HK has produced, if they felt that the flutes were not needed, I'm sure they would not have spent the extra money to flute the chambers. Of course I was four or five years old during the R&D for Project 64. So I have no direct knowledge.

Scott
 
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