How to check if rifle barrel is bent??

Swiend

Swiend

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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.
 
What I do is this ...

I put a target 100yds away and shoot a 10 shot group.
I then put up a target at my original shooting position, I walk down the 100 yards, I record whether the shots in the first 10, group to the right or left of center. I then shoot 10 shots back at the target in my original shooting position. I check this target, if the shots group to the same side either left or right, then the barrel is bent. (I cosider wind drift of course)
 
Look down the bore while pointing it at a light. You'll see a halo or shadow effect. If the shadow is concentric, then the barrel is OK, if it is more shadow in one place than another, then it is likely bent....
 
Vic777 said:
What I do is this ...

I put a target 100yds away and shoot a 10 shot group.
I then put up a target at my original shooting position, I walk down the 100 yards, I record whether the shots in the first 10, group to the right or left of center. I then shoot 10 shots back at the target in my original shooting position. I check this target, if the shots group to the same side either left or right, then the barrel is bent. (I cosider wind drift of course)
Click to expand...


Can you explain how this this relates to a bent barrel?
 
guntech said:
Can you explain how this this relates to a bent barrel?
Click to expand...


Yes .................. curious minds want to know the mechanics behind this theory. :confused:

I bet you find a lot of rifles with bent barrels testing them that way. (As well as pissing off the other shooters at the range. ;) )
 
Picture of a straight barrel

Putting you eye close to the barrel and focusing through the barrel look for a pattern of "rings" similar to looking at a bullseye on a paper target. These rings are shadows of light... some barrels show them better than others... if the rings are concentric the barrel is straight...

Here is a picture taken as best I could looking through a shotgun barrel. A hard picture to take with an autofocus camera...

This barrel is pretty straight...

insidebarrel.JPG
 
I think if you were to take a 30 inch steel rod say .001" under the bore size you would have a tough time dropping it through the barrel.
A gunsmith told me once that rifle barrels are all bent to a certain extent. You may be only talking .001-.002" of an inch over 30 inches, but they are not straight.
 
You can always pull the barrel off the action, chuck it in a lathe with the live centre and use a dial indicator (assuming that the bore is running dead centre to the outside). Maynard is correct, very few are actually perfectly straight. How bad is the barrel in question and what makes you think it's bent?
 
If the gun shoots to right bend the barrel to the left, remember...bend the barrel in the direction you want to shoot!
 
If the barrel is out of th eaction, roll it across a glass table. If you ever see any light, it may be bent. The best way is with a dial indicator though.
 
Rolling on glass is a good quick idea. You could also whip up a set up with v-blocks (home made) and a dial indicator on various positions on the barrel.

The v- block idea works well with checking used scopes before buying........
 
Heavily fluted barrels can bend easily if the take a good smack in shipping. I see it all the time. It's REALLY hard to bend a non fluted barrel. Fluted ones typically get bent right at the end of the flutes. As stated before. Most barrels are not straight. You can indicate a barrel in on the lathe but then you are using a device to hold it some what straight. There for the measurement is not relative to anything. You may see one spot that is really out. If so the entire barrel will move in that spot. Barrels are never perfectly concentric to their out side. There are too many variables to make them perfect and still be cost effective. A wire EDM could bore the hole straight but one that large would cost millions of dollars. 17" wires run about 250K.

The short end of this is to look through the barrel as already stated. If it's bent enough to make a difference you will see a slight curve. Any smith that put it on a machine should catch it right away. If it's bent you'll see it.

Some AR-15 contractors such as colt and FN straighten their barrels as a part of inspection. The barrels are so thin they put it on a hand operated press, spin it top look for the high spot, then bend it. If that doesn't scare you a little nothing should.
 
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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