Gunsmithing Hole not drilled in the center of the barrel blank?

[rrwildlife]

Hey guys,

What is the acceptable tolerance for the hole to be drilled out of center in a barrel blank? I had a 26" AMU contour barrel cut down to 22" and the hole was .022 out of center. What's your opinions? My gunsmith say's don't worry about it unless it doesn't shoot. I guess I'm curious if this is common. We so often hear about the tolerance of land to groove or bore diameter but not much is mentioned about the hole being in the center of the blank.

Thanks,

Ryan

 

[Wintermute]

I believe this is specifically why some barrel manufacturers don't recommend cutting their barrels down. Any drill will deflect over a distance (yes, even a gundrill which relies on hydraulic force to maintain shaft rigidity will deflect partially over 26 inches of hole). I don't know if there are companies out there which have a method of drilling a non-deflected bore for a barrel...it's theoretically possible, I remember a machining article regarding the use of gun drills with extraordinarily high levels of hydraulic pressure in the shaft (well above what is normally run with a gun drill) in order to drill very deep holes with minimal deflection. I don't know that any barrel shops have implemented something like this and I can only imagine what a single bit would cost in order to stand up to the hydraulic pressure load it would have to resist.

--Wintermute

 

[Geno C.]

It happens a lot more than most people think. Follow your smith's suggestion. I've seem where the barrel would be indexed to the top and saved some scope elevation.

 

[kansas]

This freaked me when I sent my Ruger 77/22 barrel to adco to have shortened and threaded for my can. Got the barrel back with a note that said "bore not in center of barrel" or something to that sort. It shot good before I had it cut down and shoots great still.

 

[Edds]

Was the hole centered in the front end of the piece you cut off?

 

[300sniper]

Hey guys,

What is the acceptable tolerance for the hole to be drilled out of center in a barrel blank? I had a 26" AMU contour barrel cut down to 22" and the hole was .022 out of center. What's your opinions? My gunsmith say's don't worry about it unless it doesn't shoot. I guess I'm curious if this is common. We so often hear about the tolerance of land to groove or bore diameter but not much is mentioned about the hole being in the center of the blank.

Thanks,

Ryan

how are you measuring it?

 

[ugsly]

I had a Kreiger barrel I cut from 28" to 20" and it was about .070 If I remember right. What wintermule said has been my experience when cutting barrels down. If I'm installing a barrel I will index the high point TDC, haven't seen one that hasn't shot yet.

Casey

 

[cal50]

If you want it concentric you turn or grind the OD between centers. Most barrels are profiled after rifling and concentricity ends up being a crap shoot. Ideally you are looking for good concentricity but the barrel OD is a cosmetic profile so it's not a priority.

 

[rrwildlife]

Thanks for the great responses. I'm not going to worry about it unless it can't get it to shoot.

 

[rrwildlife]

Was the hole centered in the front end of the piece you cut off?

I never bothered to check and left the barrel chunk at the smiths.

 

[RonA]

Sounds like one of the old Polish sniper rifles that could send a bullet out a ways and it would curve around, fly back and hit the shooter.

 

[lukus10000]

I have yet to see that the bore being off center prevents the gun from being accurate. might look funny but if it still prints .4 groups at 200 i will keep it

 

[rrwildlife]

Apparently having the hole out of center of the barrel did not affect the accuracy of this rifle either. It shoots so well I had a hard time deciphering a 300 yard ladder test. 1/2 m.o.a. or less at 300. Actually 12 rounds covering 1 1/2 grains of powder (42.0-43.5 H-4350) were right at 1 m.o.a.

 

[2Shots]

So if the barrel heats up on a bore that far off of center does the heat expand the sides of the barrel differently causing the bullet to change impact point? We've all seen a light barrel move around after heating up. But to me the farther off of center the bore is the more affect heat would have on the barrel walls that vary in thickness.

 

[rrwildlife]

So if the barrel heats up on a bore that far off of center does the heat expand the sides of the barrel differently causing the bullet to change impact point? We've all seen a light barrel move around after heating up. But to me the farther off of center the bore is the more affect heat would have on the barrel walls that vary in thickness.

So far there has been no effect. I'm shooting a Obermeyer AMU contour barrel, it's heavy. I doubt I have shot rapidly enough to heat it up to the point where I would see a change so it's possible. I have shot a couple 20 shot strings at a moderate pace (maybe a minute between shots) and I did not see a appreciable difference in point of impact.

 

[Pat M]

only a issue if you want a brake, or suppressor

 

[Glenn]

You could look at the other way!

The bore is in the correct place but the OD is off set!
Most factory barrels are like this.

As cal50 said get it turned down between centers if it worries you.

Glenn