Home Forums Hunting & Shooting Gunsmithing Bore off center

Have any of you noticed the bores of rifle barrels being bored off center. I have had several barrels from a popular manufacturer and a couple of match grade replacement barrels that had the bore off center by 0.015 to 0.020 inches. I asked a manufacturer's rep about it and he said it was fairly common when the barrel is cut back to notice it. They took the barrel back, but did not seem too anxious to do it. To me that would mean that the hole is wandering around between the chamber and muzzle. He didn't think it was funny when I asked if they normally mount the barrel with the thick side on the bottom or top. What real difference does it make? To me as the barrel�s temperature changes the group location would change too. If you sight it in on a hot summer day and then take it out and shoot it on a day where it is 30 degrees where is the group going to be? As you shoot and the barrel heats the groups would also get larger. I have looked to see if this has been addressed, but have been unable to find any reference to it.

Your overthinking this issue. All bores wander to some extent. Heating and cooling isn't going to cause the issues like your imagining. Some gunsmiths will clock the barrel with the bore pointing down on long range rifles. The barrel presently on my benchrest rifle has the worst curve in the bore of any barrels I've chambered, it's the second best barrel I've shot on that rifle.

Thanks for the info. I'm not really trying to over think the situation, just looking for some answers. I had one that was off center and the shots would string out as the barrel warmed up. When the barrel was replaced it shot good tight groups. These have all been sporter weight barrels. I guess I might have been just been replacing a bad barrel with a better one and the wandering bore was just what I could see as a problem and not the real problem. What does pointing the bore down (thick side on top?) do for a long range rifle?

Hard to predict what harmonic vibration nodes a barrel is going to display with different loads and bullets in different off-center bore positions. You would need a very large computer to model that one! If it bothers you, replace it, if not try to think about something else.

It's quite common, worry about other issues.

MtnHtr

It gives you a little more elevation adjustment with the scope.

Why is the curvature of the bore not pointing up?

Everything being equal, I like my barrels like I like my donuts with the hole in the middle. Seems like the ones I have had problems with the hole wasn't in the middle and when it was replaced with one that was centered the problems went away. If it's not a problem, as you say, then I will just chalk it up as me being eccentric which might have magnified the error caused by the bore being eccentric too and I'll do my part to boost the economy by switching it out. Thanks again for the input.

Mathsr

Considering that the barrel was drilled before it was turned to final shape, wouldn't this be a result of the final turning, not the barrel manufacturer (unless they are the same person). It seems, if all you're talking about is .015-.020", you could take it to a smith and have it trued up and your barrel would be fine, or am I missing something here?

Bob

I have never seen an off-center bore from a custom maker like Shilen, Hart, etc., I thought they turned the final shape between centers. Maybe not. I have seen off-center bores in cheap, unturned rough blanks, but when I turned them to final shape, it was between centers which made the ends bore concentric.

RAN

I don't know if they still do it, but years ago, Douglas advertised their top line of barrels as XX, and I believe they added Supreme Air Gauged to that.

In the Douglas literature, it stated that these barrels were some of the few that were actually drilled straight and didn't need straightening. Apparently, it is very difficult to drill a deep hole in a bore perfectly straight, and a lot of them (most) needed straightening.

I also remember Douglas literature stating that the gunsmith, when countouring the barrel, needed to turn them between centers, so that the bore remained in the center of the barrel. I have always done that, and I have never had a barrel that I turned with an off center bore.

As a poster above stated, the result of an off center bore would be the result of the final contouring. Some barrels are formed and turned before boring, and this could result in an off center bore.

Turning between centers should center the bore in a blank that is bored off center.

My barrel work has been limited to Shilen, Hart, McMillen, and a few factory barrels. I have never seen a barrel with an offcenter bore.

To start with I want to say that Mathsr is my brother and I have a little more information on this topic. He is dealing with custom premium grade barrels from manufacturers you would all recognize. He doesn't want this to be about a barrel maker and is not throwing stones, just trying to get informed. The barrels (2)have been ordered pre turned to a .600 muzzle and came at a 26 or 27 inch length. When cut off to 22 inches the bore was noticeably off. On the other end of the 4 inch section it appeared to be centered. We are talking .020 inch out in 4 inches. I don't know what it was out at the middle of the barrel.
This has also happened with several barrels that came on a commercial rifle and one of the problems was that the barrel was crowned concentric with the outside diameter of the barrel and not with the bore. When re-crowned with the bore they shot better groups when allowed to remain fairly cool. If you shoot a fast five they walk a couple of inches.
I am thinking it may be more of a problem with light sporters than target or varmint weight barrels, with .020 being a higher percentage of barrel mass on a sporter weight than on a target weight.

How the bore runs on the ends of the barrel doesn't tell you what is happening between them. Every gun barrel made has a portion of the bore that is a little off center. Some more so than others. Your higher quality barrels are generally more concentric. I've seen barrels, with their bores so far off center that you would become disoriented watching them spin in a lathe, shoot remarkably well.

When a barrel gets hot, they tend to walk in the direction of least resistance. The less the resistance (thin side of an off center bore), the greater the distance they walk.

"How the bore runs on the ends of the barrel doesn't tell you what is happening between them. Every gun barrel made has a portion of the bore that is a little off center. Some more so than others. Your higher quality barrels are generally more concentric. I've seen barrels, with their bores so far off center that you would become disoriented watching them spin in a lathe, shoot remarkably well."

You just nailed it (in my view, anyway)

+1

GTC

Well I can tell you that we installed a barrel from a custom premium grade maker and to the naked eye I could see the bore was off center at the muzzle and I never shot with a darn. Rebarreled the next year.

I now use only Hart or Krieger barrels. If you notice Hart only produces and sells one grade of barrel.

I've got a Hart barrel on my Rem. 700 25-284 and it is a thing of beauty. Finished barrel at 24" with a .650 muzzle, so it isn't a light sporter by any means. It shoots incredibly well (under .5) for the first 3 shots, then wanders off somewhere and forgets what it is supposed to do- until it cools, then it is back to impressive groups.

Hart barrels are very good barrels, but every barrel maker makes a lemon once in awhile.

Bob

Ok,
Nobody makes a straight drilled and rifled hole. Some are just more crooked than others. The smaller bores are the worst offender. Contouring them between centers only make them concentric at each end. Cut the barrel off and it could be off center. If you believe your pet barrel maker has sent you a perfect barrel, dial in the bore with the barrel in the headstock. Then put your indicator on the OD. It ain't gonna be perfect. I have chambered crooked barrels and in a benchrest or hunting situation found they shoot just as well. I agree with Malm, but I find no need to get my barrels hot enough to make them walk.
Butch

Spun up a new barrel for my .300 Ultramag. Stainless, button rifled in sporter weight from a popular barrel maker. Muzzle end had a tad over .015" TIR when finished. To really live life dangerously I fluted the barrel after chambering. I wanted to index the flutes so that it looked symetrical when sitting in the stock. Took the rifle to the range one afternoon to stretch her legs out to 600 yards. We have to shoot on a verification target before engaging the 600 yard target. Two shots at 600 to adjust/verify the scope setting and then a ten shot group that made me smile. Went to put the rifle back into it's case, burned a finger on the barrel. The barrel was hot (fired twelve shots in less that ten minutes)!

PLEASE don't tell that barrel it's suppose to walk shots when hot.

A recent Varmint Hunter has a great exposition on centered bores by Gordy Gritters. I've whacked a couple of barrels and seen the "drift" in the bore, yet both of them shot all right before they died.