Machining flutes on Rem .223 bull barrel

There a quite a few fluted barrels coming out of the factories these days. I seriously doubt that they are contoured and fluted before they are drilled and rifled....:)..that should tell us something.
If anyone can find out please let us know.
 
iconfig said:
sdeering, indeed.

trevj, im just a dumb machinist :) but it seems the engineers and metal metallurgists that wrote "the handbook of residual stress and deformation of steel" seem to agree with me that any milling operation causes localized work hardening. maybe you should go read what they have to say
Click to expand...

Does it say how much of an effect it has?

Lend me your copy and I'll dig into it! :)

This is it, yes?
http://books.google.ca/books?id=_a9...ual+stress+and+deformation+of+steel#PPA157,M1
Readable, but dry.
Searching through the text finds a lot of weasel words. May induce hardening. Can cause..., etc.

Mostly, reading through the references to work hardening due to machining, it looks to be a good place to start looking if we are about to start engineering the manufacturing process for turbine blades. Not so much pertinent to the discussion at hand here, though.

Any levels of work hardening that may be induced by machining processes are insignificant when compared to the stresses (and hardening, if the alloy is prone to) of flow forming the rifling, during button rifling, and those former, pale to nothingness when compared to the stresses of either cold rolling of the bar stock, or hammer forging the barrel to shape.

In short, I am suggesting that the hardening from any machining process are a red herring in this discussion. That is why I call bull! It is no more valid than your statements about heat treating.

I'm not even a dumb machinist. Not ever gonna be one either, mostly because a card will cost me money to get, that will never come back to me.
But I have been dicking around with metalworking for a hobby for about 25 years, and doing it full time as a job for nearly 10. I get to play a machinist at work, though!:D
I read this stuff because it actually interests me.

I've heard enough unsupportable theories from the mouths of instructors and "experts" to be fairly familiar with their sound and/or smell, and this one, well, it fits the mold.
Too broad a blanket statement.

There is some dry reading on the work softening of steels floating around the web too. Strange what you can find when you go look. I won't claim that it's applicable here, or everywhere else, either. :D


Cheers
Trev
 
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trev, please do point me to some of the articles on work softening of steel due to a machining process like milling. all i have found is stress relief due to reduction of compressive stress.

tev, also could you explain to me how a 4140 with no heat treating can survive a .308 win shell ?

.308 Winchester
MAP: 62,000 psi
MPSM: 66,000 psi
Minimum Proof Pressure: 83,000 psi
Maximum Proof Pressure: 89,000 psi

but if we look at 4140 with no heat treating it has a yield strength of only 60,500 psi. but if its heat treated and tempered at 600f (22HRC) it has a tensile strength of 225,000 psi and a yield which is slightly lower. so its still fairly soft and easy to machine at 22 HRC.

either it was bought already heat treated or it was heat treated after.

heh we could even get into semantics about how firing a bullet can induce case hardening
 
The refs I am finding, spec 4140 as supplied from the mill, as typically being at 28-36 Rc. That's normalized.

The barrel makers I am finding references from, are all calling for their stock to be softer than that, ranging from Lilja's 24-25Rc,as a finished product, to Hoffman at 28-32 Rc for bar stock to be suitable.

That's softer than is typically supplied. Or at least, in Hoffmans case, in the soft side of the spec. The makers that mention it, all seem to think that a finished product above 28 Rc is unwise.

Lilja says his finished product after he stress relieves, the barrel hardness tests to 24-25 Rc. Given the thoroughness of his write-ups, and the total absence of anyone else mentioning anything about the barrels being hardened in the production process, while several heat treat for stress relief, I'm quite willing to take them on their word, that that is all the heat treatment it gets after it comes from the steel mill.

Anyway, enough. I'll let you do your own math homework, re: the stresses and pressures.:)

Re: case hardening. Getting into micro-metallurgy is best done with someone that gives a damn. That ain't me. heat, carbon, and steel, in proximity. Yeah, I can see how the theory would form, but I am not equipped to prove the theory one way or the other, and nor do I care, as a good barrel will shoot and a bad one won't, and there are more theories on how to get from one to the other, than there are guys arguing them. :)

Cheers
Trev
 
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I am actually pondering the idea of trying barrel contouring. I have a lathe and the tooling for it. I talked to an Alberta barrel maker today, he states he does no heat treating.
No need when cut rifled. He said the stock he uses is stress releaved when he gets it and cut rifling puts very little stress in the metal compared to other methods (button, hamer). Makes sense to me. He doesnt charge for the contouring as long as its not to whacky.If I go the Alberta rout I will leave the barrel contouring up to him.
Any thoughts on the affects of contouring and the stress it may cause? Do other barrel makers stress releave/heat treat after the barrel is made?
Stephen
 
A barrel can be contoured using a conventional lathe and steady rest. Taper attachment or offsetting tail centre will generate the taper.
It is much, much, much easier to buy the barrel already contoured from the maker.
At one time I was manufacturing ml gun barrels, part of a reproduction ml gun manufacturing adventure. 36" long, tapered octagon, transitionning to tapered round. Started with a 36 1/4" long by 1 3/16" diameter blank. (1137 steel, FWIW). Finished barrel was something over an inch across the flats at the breech, 3/4" at the muzzle. Did all the work on a 16" SB with 56" centres. Took 2 1/2 hours from blank to breeched barrel. Lost only one barrel from springing because of release of stresses in the blank. It really warped. Impressive. Cut it short, retapered it, it is now 26", still have it. I have also contoured modern barrels.
All the old gunsmithing books have instructions on countouring barrel blanks. But it really is easier to buy the barrel contoured.
 
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