Question about contouring a barrel

[Wolfer]

In the back of my mind I have stuck that button rifled barrels can be contoured after rifling but cut rifled and hammer forged barrels are best left alone.
I could be wrong, I often am!

Is this correct?

[B R Shooter]

Actually, it's the reverse. Supposedly cut barrels can be turned down since the steel has not had stress induced while rifling like a button barrel. If you subscribe to the theory.

Unless you shoot benchrest where the utmost accuracy is demanded, I would turn down either one.

[Ballistics in Scotland]

BR is right. Cut rifled barrels can be turned down as much a you like. I wouldn't worry much about a button rifled one either, unless you want the outside to be very near the inside. Indeed those are the ones that really need to be rifled as a full cylindrical blank. It is just possible that some rifled tapered barrel forgings, for basic commercial or military barrels, but not those such as Shilen and Douglas whose customers know and expect the highest quality. The steels they use aren't cheap stuff, and if they will give you an unturned blank for less than a contoured barrel, it isn't because they want to.

The trouble is, the thin part is more likely be permanently distended by the passing of the button, while the thicker metal springs back closer to original diameter. So you get a bore increasing towards the muzzle - increasing very little, but the measurements involved in the ultimate accuracy are very small.

Hammer finished barrels vary in how deep the stressed surface layers go, but usually they form a sort of work-hardened skin, and you can't see how deep it goes, or whether it is the same everywhere. Inconsistency in this is what used to give some of the early ones, and as they have improved a lot on this, maybe they have improved also on what happens when you turn one down. But I would call the hammered finish on sporter blanks not just a gimmick or reducer of reflections, but something they can hardly afford to do without.

[seppos]

In Sako factory they use hammer forging as well as in Steyr. In Sako, the barrel blanks are first hammer forged and then turned to contour. In Steyr they first turn it to contour and Hammer forge after that.. Dont know about the accuracy of Steyrs so much, but Sakos and Tikkas should be ok.

S

[Wolfer]

Good to know.
Where this was going was my buddies Ruger MKII varmint/target in 220 swift.
My plan was/is to buy a green Mtn blank and contour to sporter dimension. Add a Boyd's classic sporter stock and it should be good to go.

The new gun will be in 22-250 thus requiring a new magizine box.

In you alls opinion could I just turn down the factory barrel?

I probably won't go this route since I could put the gun back original at any time.
I also suspect a chrome/moly blank will be a lot easer for me to turn down than the stainless factory barrel.

Thanks for all the input guys
Woody

[Ballistics in Scotland]

I also suspect a chrome/moly blank will be a lot easer for me to turn down than the stainless factory barrel.


Possibly a little, but not much. Rifle barrel steels are carefully chose for free-cutting properties, and a lot easier to work than the more corrosion-resistant stainless steels used in boat fittings etc.

[seppos]

You could turn down the factory barrel also, and the stainless is not that difficult when you use proper values. With barrels the one big problem is the vibration, so you should try to use as much support aids as possible. One option is to turn it in sections and polish the finish with emery cloth.. But do be careful as nobody wants you to be rolling around of the chuck.. Glue or stapple the emery cloth to a wooden stick so that you dont have to hold it in hand. It is very easy to roll the cloth around the barrel, and in fraction of a second you will loose skin, nails or life when the cloth rips you or part from you to the work piece.

s

[bstone5]

After the lathe work to get the barrel to the desired shape it is a good practice to sand the barrel with a barrel spinner tool and a belt sander. The spinning and sanding will give the barrel a good finish and bring the barrel to a dynamic balance. The barrel while being spun and sanded will take all of the wabble out of the barrel. This process will make the barrel shoot better.
Over the years this process has proven to be a good practice for a more accurate shooting barrel.

[MarkP]

I toured Doulas Barrels in the late 90's they stress relieved their barrels. Sealed both ends with some type of refractory clay and placed in the oven to soak and slow cool.

[Wolfer]

I built a tool holder for my lantern style post that clamps to a 4-1/2" grinder. With a sanding disc on the grinder I can run it with the carrage and it works pretty good at cleaning up my poor lathe skills.

[seppos]

Wolfer.. that is good to hear. You should use the steady rest if you have one. If you turn it in sections support the previous section with steady rest and turn the next one. After that move the steady rest forward so that you always have the support from it so that the barrel does not start to vibrate. Follow rest would be super, but those tends to be rare.. One could make one but have to think that if the barrel will have long taper, also the bearings should follow the contour (be supported by spring tension).
If you only do one barrel it might not be wice to construct the follow rest, but if you will be doing it often, that is worth of thought.

S

[Wolfer]

I have a homemade steady rest which I use a lot. I don't have a follow rest but could make one.
Factory parts for my 1894 lathe are rare to non existent.

My plan has always been to turn in short sections and blend in with the sander.

After I pass the halfway point I could move the steady rest behind the carrage and work on to the chuck. More than likely though I'll turn the barrel around and work both ends from the tail stock. My old china made 3 jaw chuck has a few thousands of run out and the only place I trust is between the tail stock and the steady rest.

This might be a good place for me to turn between centers with a lathe dog huh?

[Ballistics in Scotland]

I built a tool holder for my lantern style post that clamps to a 4-1/2" grinder. With a sanding disc on the grinder I can run it with the carrage and it works pretty good at cleaning up my poor lathe skills.

This is close to the ideal, I think. Well, a purpose made toolpost grinder from the makers of the lathe is ideal, but they are very expensive for occasional use, and the makers of your lathe have passed away, leaving no forwarding address.

You could, I suppose, use a hand-held belt sander on the lathe, but I wouldn't unless I found a wood turning lathe cheap enough to devote to this purpose. It is too easy to get grit into the delicate internals of an engineer's lathe. An unpowered barrel spinning fixture is practically as good, and easily improvised with a couple of pillow block bearings. You can adjust the speed at which the barrel rotates, and the speed of sanding, by changing the angle to the barrel at which the sanding belt travels. If it comes to that, the best shotgun makers, who can't afford any variation in barrel wall thickness, used to let the barrels spin by hand against a large, cutlery-industry style sandstone wheel. You could do the same with a bench mounted belt sander.

[KCSO]

To clean up a rough turned barrel you use a shear tool and just take off the final 2-3 thousands. Either barrel will turn but when I do a button rifled barrel I try not to get it hot while working.

[Cap'n Morgan]

I've seen a gunsmith put a very nice finish on a barrel, by holding it with two handles with ball bearings and let it spin against a belt sander. Even if the belt was quite coarse (60-80 grit I think) the surface was surprisingly shiny and smooth and the process took less than a couple of minutes.

[John Taylor]

All the button rifled barrels that I have seen are stress relieved except for some from Bauska years ago. Cut rifle barrels do not have stress when rifled.Most of the big rifle companies are using hammer forged barrels. I'm a dealer for Green Mountain and use their barrels when they have one that will work. I contour barrels almost every day and have had no problems with turning or octagon barrels shooting bad. I use carbide tooling most of the time and a band sander for polish.

[Alan in GA]

IMO the extra $30 one can pay the blank / barrel maker to contour it is well worth the cost. Buy it in the contour you want and then just have the surface finish you want to do on your own lathe. I've taken ONE full contour blank to heavy sporter contour and won't do that again.

(I'm not a real machinist, but I play one on the internet... LOL)

[ulav8r]

Ordered a heavy contour barrel from Douglas, when it arrived about 1/2 the length in the middle had a deep spiral pattern of grooves around it. It was the worst case of chatter I have ever seen. I decided in the future I would order polished barrels, hoping they would use ones that did not have so much roughness to remove.