Stress Relieving a Barrel After Contouring

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Allen Gun Works

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I am going to be buying a barrel blank for a project. I am going to need to turn it down to the desired taper and then get some "special" fluting done (my head is full of "great" ideas). Anyway, will I need to get the barrel heat treat and/or stress relieved when I am done?

If either or both of these are necessary, a good machine shop should be able to do it, right?
 
Why not just get the barrel maker to do that for you. At least that way you are not at fault if it doesn't shoot.
w ww.cryointegrity.com
 
Before the barrel maker ships the barrel it will be stress relieved. It is part of the barrel making process.

If it for some reason has not been stress relieved properly, you will not successfully turn the diameter down as each pass of the cutting tool will cause it to warp in a different direction.

Stress relieving is not required after turning down a properly made barrel.

I have not encountered an improperly stress relieved barrel since about 1968 or 69. I had a .375 barrel blank from Ackley that warped all over the place. It ended up looking like a crankshaft and Ackley replaced it and commented that it had not been stress relieved.
 
Good to know. I am ordering a Montana blank. I have used them once before and it worked out ok. I just want to be on the safe side and cover all of my bases. I am going to ensure the machine shop uses the proper cooling methods.

To answer the question of "why not just let the barrel make do it?".........I want helical fluting, none of the barrel makers in Canada offer that. I don't want to order from the US if I can help it.
 
guntech said:
Before the barrel maker ships the barrel it will be stress relieved. It is part of the barrel making process.

If it for some reason has not been stress relieved properly, you will not successfully turn the diameter down as each pass of the cutting tool will cause it to warp in a different direction.

Stress relieving is not required after turning down a properly made barrel.

I have not encountered an improperly stress relieved barrel since about 1968 or 69. I had a .375 barrel blank from Ackley that warped all over the place. It ended up looking like a crankshaft and Ackley replaced it and commented that it had not been stress relieved.
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True that barrels should be stress relieved as part of the process. However once you start contouring and fluting, you are putting stress back on the barrel. Any machining process will put stress on metal with the exception of EDM (Electrical Discharge Machine).

Other then looking cool, what does helical fluting do to the harmonics of the barrel? Would the flutes be timed to the rifling? Would machining them in the opposite direction of the rifling effect anything. Would cryogenic deep freeze help maintain a straighter barrel oppossed heat treat?

The reason I ask is that I have a barrel that makes my rifle over-weight for the 6.5 Kg target rifle limit. The barrrel was changed out to a lighter profile but the old barrel shot better.
 
In the industry, this sub-zero stabilizing treatment of steels is a lengthy process, and is mostly use to stabilize hardened gages en delicate measuring tools, whether or not it has any beneficial effect on the tools is debatable.
And, in my humble opinion, dumping a gun barrel into a liquid nitrogen bathe for a couple of hours would have no effect on the barrel material or its accuracy.
 
maynard said:
True that barrels should be stress relieved as part of the process. However once you start contouring and fluting, you are putting stress back on the barrel. Any machining process will put stress on metal.

The reason I ask is that I have a barrel that makes my rifle over-weight for the 6.5 Kg target rifle limit. The barrrel was changed out to a lighter profile but the old barrel shot better.
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Could you explain your theory please.
More than once I have taken a full blank that was properly stress relieved and turned it extremely light and it stayed dead straight...

I think the reason your lighter barrel did not shoot as well as when it was heavier was mostly due to it being lighter. Stress relieving it again would not change that.
 
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lighter barrels=whippier barrels
the stiffer the better, I agree with guntec your light hunting rig isn't going to shooting with a heavy barreld rig.
 
Guntech, Not a theory, fact. Any machining puts stress on the steel. I am not saying if you turn a true barrel blank it will warp or bend it, but you are putting stress to the barrel. If you were it take the turned barrel and have it stress relieved again, it may or may not be straight.

I think Kreiger at one time stress relieved their barrels once before rough contouring and again after. Both cryogenic stress relieve. I don't know if they still do this or if it was just a fad 8-10 years ago.

Duck hunter
I went from a 30" Heavy Palma Contour barrel to a new 30" Regular Palma Contour barrel. The rifle weighs about 3 oz lighter with the new aluminum stock. I can say for sure the other barrel was better, just on V count.
 
You know, I've said this before but I will say it again anyway. Machining does not add stress to the barrel UNLESS the machining is done with a dull tool which displaces metal rather than cutting it. Machining removes material and, with the material, removes any residual stresses. When the stresses are removed, the material moves. When material is properly stress relieved, it is mostly inert. I say "mostly" because the stress relief process may not have been perfect and there may be some residual stress in the blank.
I once had to machine some steering racks with integral hydraulic pistons. For this I ordered some HTSR 4140. The piston was 1 1/4 in diameter while the rack was .750 and about 32 inches long. The teeth were cut about 35% of the way through. I made 3 of them and the first one warped pretty badly. I stress relieved the other two pieces of material by putting them in a piece of 6" tubing and heating it with a tiger torch until my RadioShack heat sensor thingy showed it to be at about 1100 degrees then I covered it all in sand and left it overnight. The pieces machined from this material stayed nearly perfect even when I cut the teeth in the shaft. Obviously the machining was not inducing stress. The stress was there in the first place on the first piece of material and the machining only allowed the stresses to have an effect.
By the way, MRC barrels are properly stress relieved. I've seen their furnace and seen it in action. I've also turned their barrels with minimal movement.
Barrel makers usually use material which is stress relieved prior to working on it. Some will have it relieved again after drilling. Those makers who produce button rifled barrels must stress relieve after buttoning since buttoning does introduce stress into the barrel. This is because it is a swaging or metal displacing procedure. Those barrels which are cut rifled don't generally require stress relieving after rifleing. That is, they don't if the material was properly stress relieved to start with.
Cryogenic treatment is not true "stress relieving". It may have some effect but seems primarily geared toward improving machinability and surface finish. Regards, Bill
 
Leeper's experience concurs with mine. You can remove residual stresses by machining but you are not inducing new stresses....unless you use dull tools etc...

The last time I fluted barrels...three of them.....I measured what little TIR there was at the middle of the barrel before and after the fluting...neither barrel moved more than what can be seen on a common .10" per revolution dial indicator.....probably a couple tenths if anything and they all shot as well after fluting as before. These were two King barrels, a .224" and a .358" and a 284" Gaillard.

IMHO...this whole stress thing with recontouring and fluting is an old wive's tale propagated by people who have either had a bad experience..ie: one bad barrel...or have never done any real machining.......

besides...how the he11 do you think barrel makers contour thier own barrels?..most, if not all,.. are contoured AFTER the drilling, reaming and rifleing procedures..
 
Lots of good info in this post. Glad I asked!!! I guess the long and short of it is....as long as the machining is done with sharp tools, the barrel blank has been properly stress releived prior to machining and proper cooling methods are used, the variations in the inside geometry will be negligible.

I also found this page which has some really good info............

http://www dot border-barrels dot com/
 
Rembo said:
IMHO...this whole stress thing with recontouring and fluting is an old wive's tale propagated by people who have either had a bad experience..ie: one bad barrel...or have never done any real machining.......

besides...how the he11 do you think barrel makers contour thier own barrels?..most, if not all,.. are contoured AFTER the drilling, reaming and rifleing procedures..
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I have been a tool maker for 25 years. I earn my livelihood as the owner of a machine shop. "or have never done any real machining......." I don't think so.

I stick firmly to my statement. (Edit to capital letter is not shouting:wave:)

"Any machining puts stress on the steel. I am NOT saying if you turn a true barrel blank it WILL WARP or BEND it, but you are putting stress to the barrel. If you were it take the turned barrel and have it stress relieved again, it MAY or MAY NOT be straight."
 
maynard said:
"Any machining puts stress on the steel. "
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You keep saying that - you must believe it. :D ... But please offer some arguement, some facts, other than just saying that. Quote a source...

The little I have read about creating stress indicated that considerable heat was involved, usually in a grinding process.

My opinion sides with Mr. Leeper on this.
 
internal stress relieved before machining, only remains until new shape parameters are created, these parameters no matter how sharp the tool is creat new stresses, this is a known result and is why various methods are used in tool/die mold making on finished hardened parts to remove existing stresses before functional work is done and if this actual wok is heavy duty the part should be stress relieved during duty cycles. Stress relieving before machining is done to enhance machining conditions and stability. Good maching practise as on turbine shafts stress relieve[SR], rough turn, [SR], Heat treat [SR], finish grind, [SR] to operating temperature and dynamic balance
 
From what little I understand on the subject, I've been led to believe that button-rifled and cut-rifled barrels are very different on the issue of stress.

Cut rifling is supposed to be superior because it simply cuts metal away and therefore does not induce stress into the barrel blank. This is why apparently blanks can theoretically be cut rifled in their contoured form and do not need to be stress relieved after the rifling process is finished.

Button rifling is supposed to be another matter entirely. It adds major stress to barrel blanks. Essentially, it inolves the pushing of an oversized plug through a tight bore with a twisting motion. The process literally "squashes" the rifling into the barrel. The metal that is "squashed away" during the rifling process has to go somewhere -- and that is where the stress comes in. This is apparently why the buttoning process works best with full cylinder blanks. If one part of the barrel is contoured lighter than the other, then the "squashed metal" will be more inclined to flow in that direction and unevenness will result in the straightness of the barrel as well as the uniformity of the bore diameter.

Apparently, this is why button rifled blanks are contoured AFTER rifling, and are often then stress relieved.
 
p-17 said:
Apparently, this is why button rifled blanks are contoured AFTER rifling, and are often then stress relieved.
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I am not sure but after the button rifling process I think they are first stress relieved and then contoured and hand lapped ....
 
The engineering definition of the term "stress" is force per unit area. All forms of metal working weather it be a "cutting" operation or a forming (metal displacement) operation such as broaching (button rifiling) MUST involve a certain degree of "stress", otherwise the metal would not get "worked". A cutting operation with hard, sharp bits, with proper feed rates, and adequate lubricant/coolant will normally result in less stress to a lower depth, compared to a forming displacement operation such as broaching.
 
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