Recontouring a barrel and its effects on accuracy.

[wildchild]

Does anyone have experiance with having a barrel recontoured and experiencing accuracy loss?
I have a 6mm heavy varmint contoured barrel and going to have it turned down to fit a AR15 upper.
I did this with my 30 major in my AR and it hammers but hey....what slow twist 30 cal don't?

 

[Preacher]

I've done a few and never had a accuracy issue with them, but they were turned down really slow a little at a time...

 

[JDMock]

According to Mr. P.J. Hart (Hart Rifle Barrels), turning the outside causes the bore to grow in diameter. The barrel is lapped to its final dimensions after it is contoured. Krieger turns his barrels before drilling the bore. If I were to try to turn down a barrel, I would do as Preacher suggested and go very slowly. Good shooting.. James

 

[Macropod]

It depends whether it is a button or cut rifled barrel. Button rifled barrels will have more internal stresses to potentially cause bore dimension changes.

 

[wildchild]

Mmmmm, grows in dia. I'll slug the barrel before and after with same slug and we will see..

 

[Tim s]

If this is a SS buttoned barrel it will likely be ruined if you go more than a few thou on the profile. The bore will, indeed get bigger, but the interior dimension will allso go all over the place from one end to the other because of all the stresses you will release.

 

[6fatrat]

I turn down shot out match rifle and LR prone barrels on a regular basis in my shop.
These barrels shoot great, the condition of the barrel and the machining method used are the deciding factors.
Steve Bair

 

[STS]

I get a big chuckle out of threads like this one. I've turned down 1.250 and 1.350 diameter button rifled unlimited BR barrels to #7 taper dimensions and have never ruined any of them. Every one of them shot extremely well in their new role in life. It's a pain in the rear end doing it, but it is in no way as critical as some people think it is. I know of one barrel that was a 30 cal. buttoned HV taper barrel that was turned down to a 6 taper so it could be used on a Hunter class BR rifle. That barrel won the 100 yard stage of the Hunter Nationals a couple of years after it was recontoured.

 

[6MMWASP]

This is a turned down 1-14 Krieger from a LV contour to a Remington Magnum.

In a LVSF stock.

 

[stansrifles]

If this is a SS buttoned barrel it will likely be ruined if you go more than a few thou on the profile. The bore will, indeed get bigger, but the interior dimension will allso go all over the place from one end to the other because of all the stresses you will release.

Wrong if a button barrel is properly stress relieved if you turn it down to a smaller contour providing it is a slow process or if it is flooded with coolant it will not open up.
Stan

 

[SDWhirlwind]

Well, guess I will add my 2 cents worth. Have bought several straight contour blanks because I got them cheaper and with no wait time and recontoured them from HV, M40, Rem Var. From Schneider to Obermeyer to Krieger, to Shilen, to Douglas to Border with no issues. All were stainless. Got lucky maybe!!!!!

Bought a 40-XB stripped barreled action off GB advertised with "surface rust" on barrel. Figured the receiver was worth the $240 I pd shipped.lol Bore looked great though.Thought as they are straight taper I could take .010 to .020 surface cut full length and have it coated. Well when set up between centers the 28" barrel had about .020 curve/bow in O.D. So I wacked off 6" and recut it to a 'heavy sporter'. Muzzle diameter roughly .750" from original .90ish". Top target shot prior to tearing it down with mini mags, Green Tag and Federall 711, nothing expensive. Bottom target shot afterwards with Mini-mags and Wolf and I think I shot some 711 on another target also??? Some of the targets have 2 separate groups using different ammo etc, I was lazy and it wasn't from shooting to 2 different POI. Memory no good no more. Anyhoo with a T-10 and both stocks I used were previously bedded but not for this barreled receiver, just something it fit in. It shot as good or better after my inexperienced machinist skills butchered it up!!! NOT a guarantee or anything, just proof that all the hype about recontouring anything other than cut blanks might not hold much water. Only target ammo or worse and not match, only 10X, factory trigger, not perfect bedding and I have a 3 leade pacer/defib that induces horizontal of 1/2" or so @ 100yds generally. In other words it done pretty good considering everything IMO!!!!





Would agree with Stansrifles, a lot has to do with setup and how you go about it. All my recontouring has been done on my Atlas 36" as I don't have a taper on either of them and it is easiest to move tailstock and reset. Cheezy lathe but light cuts and stop to allow cooling after 3 passes or so. I setup steady and only do about 8" at a time and spend some time with files and emery to get nice finish. Not a money making way but I got way more time than money or machinery.

Respectfully,
Dennis

 

[JDMock]

Anecdotal evidence of turned down barrels remaining accurate not withstanding, Mr. Hart stated that the bore grew when metal is removed from the exterior. He based this on expensive air guage equipment that can measure in 50 millionths of an inch or smaller. Even fluting of a barrel can cause expansion.
Barrels can be turned down and retain accuracy, but with the extreme accuracy required in competition today, I would not turn a match barrel to a smaller diameter. Good shooting....James

 

[SteveOak]

According to Mr. P.J. Hart (Hart Rifle Barrels), turning the outside causes the bore to grow in diameter. The barrel is lapped to its final dimensions after it is contoured. Krieger turns his barrels before drilling the bore. If I were to try to turn down a barrel, I would do as Preacher suggested and go very slowly. Good shooting.. James

I used to be a 'Shop Rat' at a well known barrel makers. I got to see the entire process from steel arriving in 10' lengths to cutting to length, drilling, rifling, profiling, chambering and fitting to an action.

Every single barrel was drilled and rifled first and then centered on the drilled hole and profiled. Every single one.

Ugly little secret. The technology to drill a perfectly straight hole through a 30" blank does not exist. You drill the hole and if the point where the cutter exits the other end of the blank is "not too far off" you use it for a barrel. The hole is neither through the middle of the bank nor perfectly straight.

 

[Ggmac]

They may be drilled and rifled then turned but they are hand lapped AFTER profile .

 

[SteveOak]

They may be drilled and rifled then turned but they are hand lapped AFTER profile .

Lapping would make the bore larger. Not sure I see your point.

 

[bheadboy]

I had a 26" 222r hart 14 twist bbl HV on a 40x, after about 1850 rounds it still would go under .200 frequently when I did my work, then I move, stopped BR comp. (college tuition) -- later took the bbl off, shortened to 22" had chambered to 221 and reduced the contour to lighten - Hart did the work, re installed on the 40x action

I would still shoot in the high .100 and low .200.s when I did my work

the possibility of "loss" accuracy I attribute to 221 vx 222

Great PD rifle.

Bob

 

[johara1]

Anecdotal evidence of turned down barrels remaining accurate not withstanding, Mr. Hart stated that the bore grew when metal is removed from the exterior. He based this on expensive air guage equipment that can measure in 50 millionths of an inch or smaller. Even fluting of a barrel can cause expansion.
Barrels can be turned down and retain accuracy, but with the extreme accuracy required in competition today, I would not turn a match barrel to a smaller diameter. Good shooting....James

James, I think i would take Stans advice, as the co. he works for showed Hart how to make barrels……….. jim

 

[Ggmac]

Match barrels are hand lapped after reaming and rifling . The hand lap barrels are reamed slightly smaller to allow for hand lapping . ER Shaw , Wilson , green mountain , do not hand lap barrels , still they shoot good and everyonce and a while one will shoot great . If you bore scope barrels that have been hand lapped you can see the dif .
There have been some discussion lately about turning the barrel and threading for a brake , this too opens up the bore . Does it really matter? I don't think most would ever know , but I don't think it helps . Given the choice between the 2 I would want the one that has the same bore diam or at least a slight choke at the muzzle .
A good read on this topic and others is Rifle Accuracy FACTs , by H . Vaughn

 

[savagedasher]

Barrel manufacturing has just arrived to the 21 century Thanks to Sunnen Larry

 

[stansrifles]

What is the sunnen process of rifling.
Stan