How to check if rifle barrel is bent??

Swiend said:
Hello all, I remember reading here about a method to check if a barrel is bent using dim light down the bore. I can't find the thread in question, can anyone help?
thanks.
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I am afraid you are incorrect Dennis (Guntech)

We are talking about a bent barrel. Not a bore which is eccentic with the OD of the barrel. Are we good with that?

Bent is bent after the fact. Not a function of drilling/turning. Fair enough??
 
### International said:
I am afraid you are incorrect Dennis (Guntech)

We are talking about a bent barrel. Not a bore which is eccentic with the OD of the barrel. Are we good with that?

Bent is bent after the fact. Not a function of drilling/turning. Fair enough??
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Don't be afraid... it is just my opinion based on what I have been taught and observed over the years...

When manufactured the bore may not always be straight. The factory may straighten the barrel after manufacturing. I have looked through a barrel where the bore appeared very straight but when spinning the barrel on centers the outside was considerably off in the center of the barrel although the ends were concentric.

Large barrel straightening machines will "bend" the barrel straight but the straightness is determined by operator looking through the bore.

If bending the barrel straight is done after the barrel is manufactured, the outside of the barrel will appear bent while the bore will not. Fair enough?
 
guntech said:
Don't be afraid... it is just my opinion based on what I have been taught and observed over the years...

When manufactured the bore may not always be straight. The factory may straighten the barrel after manufacturing. I have looked through a barrel where the bore appeared very straight but when spinning the barrel on centers the outside was considerably off in the center of the barrel although the ends were concentric.

Large barrel straightening machines will "bend" the barrel straight but the straightness is determined by operator looking through the bore.

If bending the barrel straight is done after the barrel is manufactured, the outside of the barrel will appear bent while the bore will not. Fair enough?
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Holy smokes Dennis.......the other techniques described will diagnose the problem easily.

But to answer your question, not really. You are completely in error with respect to the posted subject matter. The gentlemen posted "bent." Pretty simple but if you want to go on, fill your boots.

WE ARE TALKING ABOUT A BENT BARREL and NOT manufacturing issues.....those were discussed later on...
 
### International said:
Holy smokes Dennis.......the other techniques described will diagnose the problem easily.

But to answer your question, not really. You are completely in error with respect to the posted subject matter. The gentlemen posted "bent." Pretty simple but if you want to go on, fill your boots.

WE ARE TALKING ABOUT A BENT BARREL and NOT manufacturing issues.....those were discussed later on...
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Joe, the original question was:

Hello all, I remember reading here about a method to check if a barrel is bent using dim light down the bore. I can't find the thread in question, can anyone help?
thanks.

Joe, although I did not have a link to the thread he asked about, I think my answers were appropriate and accurate.

In my experience a lot of factory barrels will appear crooked in a v block but the bore will be straight... I also have seen them spin very true but when you look through them, the bore is bent... they simply vary too much to rely on an outside dimension to establish straightness...

and it boils back to how to determine if a barrel (bore) is straight... and that is done by looking through the bore...

Joe, I don't understand you. I observed previous threads you were involved in with very arguementive behavior, and because of that I am not going to argue with you or respond to any of your posts from now on. You can fill your boots all you want. I am out of this thread...


.
 
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If I can slightly modify guntech's method; what I have seen described in various books is to look down the barrel at a straight line such as a string. If the shadow the straight line casts, inside the barrel, travels the whole way down the barrel, the barrel is straight. If the bore is bent, the shadow line will stop at the curve.
While top quality modern barrels may have the bore centered on the outside, you can certainly find factory seconds with considerable drill run out. If you buy these as a blank and try to turn the outside concentric with the inside, you may be removing stress from the surface and creating a bent barrel from one which was straight (in my experience). A barrel which was cold rolled into shape will often have these stresses in the surface as opposed to a barrel which was milled or turned to shaped before straightening.

cheers mooncoon
 
guntech said:
Rolling on glass and indicating on the outside of the barrel do not check if the barrel is straight... those methods only check the outside surface which does not always relate to the bore....

When barrels are straightened it is determined by sighting through the bore... the outside has nothing to do with it...
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Dennis. Sorry you feel that way and sorry if I offended you. The post highlighted above (first sentence) is the one that is wrong. I think you might want to re-evalutate the situation and particularily the statment. Don't take it personally.

The technique mentioned by another poster is certainly suitable for the application.
 
I will add one thing to what Guntech has said about observing barrels BY LOOKING DOWN THE BORE. Clean the bore to bear metal. You want that bore as shiney as possible.

I hold up the barrel just off center of a incandesant light bulb. I find the yellow light easier to see shadows with. You want to see well centered 'circles' down the length of the bore. Look for rough spots or chunks missing from the lands. Believe me, if they are there, it wil be very obvious.

If you can, rotate the barrel through 360deg while looking at the light. The circles should not change. That bore is as true was the naked eye is going to see. And this method is surprisingly very accurate.

If the bore is not true, you will get shadows or the circles will 'collide' along the way. By rotating a few degrees either way, you will see this as a distortion or moving shadow/blurr. Is this servere enough to toss the pipe? I would shoot it first to find out.

Also, have a look just infront of the chamber. Are the lands even all around the throat? Are there visible chunks missing or one land ahead of the others? Any lumps in the rifling indicating carbon buildup?

Without a bore scope, these are the simple things that you can do at home to see really gross problems in your bore. Personally, I don't sweat alot of what I see in the bore. I shoot the rifle and make my decision by what I see on paper.

And yes, bending the barrel to straighten the BORE is used by ALOT of rifle and barrel manf. The viewing method described above is what is used to set the bores true.

And yes, many barrels have a bore that is not true to the outside of the barrel. One big reasons, groups grow or string when the barrel gets hot - warpage.

Jerry
 
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Thanks for all of the replies. The rifle in question is a bubba'd (but nicely done) K98 Mauser. The bore is perfect but not a single part matches. The rear site was removed (torch method). I had a one piece scope mount installed but I mounted the scope personally. When sighting in the scope, I basically had to max-out the scopes windage to the right. Thankfully I can adjust the rear scope mount to compensate. (could be the used 4X Tasco's fault?) Another hint is an uneven gap along the barrel and the stock. (it's a cut down WWII laminated stock)
I'll try the above mentioned methods and post the results.
 
he rifle in question is a bubba'd (but nicely done) K98 Mauser
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if it retains the typical Mauser 98 "steps" in the barrel... rolling it on glass isn't going to help a whole lot....if the barrel has been turned to remove the steps...you probably have other problems.

Personnally I would agree with gunasauras...it is not unusual for the mounting holes to be off even when someone tries to use a jig. .... drill bits can wander when trying to penetrate to surface of a normally hardened 98.
The expedient solution is a set of Burris "Z" rings with the offset inserts to get your scope "Bore-sighted" and the adjustments of the scope "centred" ... then go from there. If it groups ok...you have a shooter...my 2 cents.


Edit... btw the Mauser factories routinely straightened barrels prior to assembly....they did it with large barrel straightening "jigs" and a judicious peer down the bore....
 
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guntech said:
Rolling on glass and indicating on the outside of the barrel do not check if the barrel is straight... those methods only check the outside surface which does not always relate to the bore....

When barrels are straightened it is determined by sighting through the bore... the outside has nothing to do with it...
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I'm not a barrel expert and I dont play one on TV but what Guntech said makes sense to me anyways.

If you drill and rifle the bore and then do the OD that means the barrel is stright in the sense if you have it on 2 centers on a lathe, but if the bore wasnt stright and you needed to strighen it by bending it that means the OD isnt stright anymore in relation to the 2 centers throughout the whole OD because its been bent.

Look at this picture the first barrel is stright after contouring of the barrel before strighting in relation to the centers in the bore. But after bending to make the bore stright the bore isnt stright anymore. (sorry about the picture it was a quick little sketch).

Barrelbend.jpg

The red like represents the center point of the barrel in relation to the OD which is on centers.
The triangles are centers.


I hope what I said makes sense.

Dimitri
 
Yep, there's a difference between an off-axis bore and a bent barrel. if it's BENT outright, then measuring the outside of the barrel will let you know. If it's got an off-axis bore then it won't.

Is it possible to have a 'bent' bore? For example a barrel that's perfectly true on the outside, and the bore is perfectly true on each end but bows in the middle?
 
Is it possible to have a 'bent' bore? For example a barrel that's
perfectly true on the outside, and the bore is perfectly true on each end but
bows in the middle?
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To my knowlege it isn't only possible but it is the general rule cause barrels
outside is lathe turned after the bore is drilled. The outside is then turned by
centering on the bore ends so everything looks concentric, but when you cut a
barrel to shorten it you see the bore isn't concentric all the way long.

Jocelyn.
 
The british determined, after a lot of testing that provided the last 6"of the barrel were straight, the rest did not matter. They then provided special testing gauges for this purpose.

Provided your rifle shoots straight, I would not sweat it!

See Skennerton, "The Lee Enfield Story" p201.
 
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