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determining the straightness of a bore.

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rmann

32 Cal
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Newly purchased Colerain barrel: 42" .40 "A" wt. swamped barrel, outwardly bowed a bit to the right. How do I determine if the bore is straight? It appears to bow the same, but might be my imagination. Thanks for help!
 
Old School Methods:

Remove the breech and look down the barrel at a white piece of paper, and you might see an actual bore bend..., if not then...,

Measure the thickness of the barrel walls at the breech and at the bore, for each of the 8 flats.
IF the bore corrects for the bend, then it may show at the muzzle and breech, by measuring the width from the bore to one side of the flat. It mayl be less than on the opposite side, and at the breech the measurements will be reversed.
MEASURE BARREL.jpg


OR, you get a rod .35 diameter x 24" and drop it down the unbreeched barrel. If there's a bend it will not drop through...,

Modern Method:
Shine a lazer down the unbreeched bore and see if it hits the walls or travels through true.

LD
 
You're right that swamped barrels can be a bit deceiving that way.

Set it down on something known to be hard and flat (a table saw table is a good one for instance) and measure the height (or gap) in the swamped section. Then flip it over and repeat on opposite sides. If there's a difference, (beyond instrumentation reading error of a couple of thousandths) it's bent.

You're lucky you spotted it before you had done a lot of work on it like cutting in lugs, tang, touch hole, and sights. You can return it and probably get another in relatively short order. Colerain is a big enough manufacturer with relatively tight manufacturing tolerances that what they send you as a replacement will probably fit pretty well in to the barrel channel that's already cut (if it is already). They're also big enough that you probably won't have to wait an extraordinary length of time for a replacement, and they have the finances and reputational risk on the line that they will probably stand behind their product. (Forums like this with a small community can be bad things for a company that way.)

I got one from a smaller manufacturer that I didn't find out it was bent (my fault for not checking it sooner) until I had done the whole build. He offered to refund my money, replace, or straighten it though. But, because it took him 2 years to make and ship it in the first place, (one got lost in the mail, and another bent all up when he was making it), and the build took me 2 years to do, I didn't want to take the chance on another mishap while it was out of my custody, so I did the straightening myself. Not hard to do, but I had to learn how. It was a bit of a "pucker factor" process, but it came out ok in the end.

As a FYI; mine was quite visibly bent once I really looked at it. Like you, I thought it was an optical illusion (with the flats) when I first looked at it. But as it turned out, it was so much so that the front sight had to be way over to one edge of the top flat, and the back notch way over to the other side to center the shots at 25 yards. So the proof was in the shooting. I just didn't believe my eyes until I actually shot it.
 
Last edited:
Old School Methods:

Remove the breech and look down the barrel at a white piece of paper, and you might see an actual bore bend..., if not then...,

Measure the thickness of the barrel walls at the breech and at the bore, for each of the 8 flats.
IF the bore corrects for the bend, then it may show at the muzzle and breech, by measuring the width from the bore to one side of the flat. It mayl be less than on the opposite side, and at the breech the measurements will be reversed.
View attachment 38764

OR, you get a rod .35 diameter x 24" and drop it down the unbreeched barrel. If there's a bend it will not drop through...,

Modern Method:
Shine a lazer down the unbreeched bore and see if it hits the walls or travels through true.

LD
Old School Methods:

Remove the breech and look down the barrel at a white piece of paper, and you might see an actual bore bend..., if not then...,

Measure the thickness of the barrel walls at the breech and at the bore, for each of the 8 flats.
IF the bore corrects for the bend, then it may show at the muzzle and breech, by measuring the width from the bore to one side of the flat. It mayl be less than on the opposite side, and at the breech the measurements will be reversed.
View attachment 38764

OR, you get a rod .35 diameter x 24" and drop it down the unbreeched barrel. If there's a bend it will not drop through...,

Modern Method:
Shine a lazer down the unbreeched bore and see if it hits the walls or travels through true.

LD

Thanks Dave, I tried your simple suggestion of just looking down the barrel at a white surface, and it looks straight. I had been looking through the bore at bright light, or outside in the daylight, and that wasn't as clear. So that was helpful. I couldn't detect any noticeable run out in either breech or bore, but I should break down and buy a vernier caliper.... I'll talk to Colerain and get their imput. I don't have a laser or straight steel rod of the appropriate size around, but I can check with friends. Thanks again.
 
You're right that swamped barrels can be a bit deceiving that way.

Set it down on something known to be hard and flat (a table saw table is a good one for instance) and measure the height (or gap) in the swamped section. Then flip it over and repeat on opposite sides. If there's a difference, (beyond instrumentation reading error of a couple of thousandths) it's bent.

You're lucky you spotted it before you had done a lot of work on it like cutting in lugs, tang, touch hole, and sights. You can return it and probably get another in relatively short order. Colerain is a big enough manufacturer with relatively tight manufacturing tolerances that what they send you as a replacement will probably fit pretty well in to the barrel channel that's already cut (if it is already). They're also big enough that you probably won't have to wait an extraordinary length of time for a replacement, and they have the finances and reputational risk on the line that they will probably stand behind their product. (Forums like this with a small community can be bad things for a company that way.)

I got one from a smaller manufacturer that I didn't find out it was bent (my fault for not checking it sooner) until I had done the whole build. He offered to refund my money, replace, or straighten it though. But, because it took him 2 years to make and ship it in the first place, (one got lost in the mail, and another bent all up when he was making it), and the build took me 2 years to do, I didn't want to take the chance on another mishap while it was out of my custody, so I did the straightening myself. Not hard to do, but I had to learn how. It was a bit of a "pucker factor" process, but it came out ok in the end.

As a FYI; mine was quite visibly bent once I really looked at it. Like you, I thought it was an optical illusion (with the flats) when I first looked at it. But as it turned out, it was so much so that the front sight had to be way over to one edge of the top flat, and the back notch way over to the other side to center the shots at 25 yards. So the proof was in the shooting. I just didn't believe my eyes until I actually shot it.
Thanks Col, Yeah I checked with a straight-edge after I noticed the discrepancy, and that confirmed my eye. Measuring the gap from the "waist" of the swamped barrel to the straight-edge: left side .031, right side .078 That's a 5/64 difference! But looking through the bore at a white paper, My eye doesn't detect a bend. I should check with Colerain. Maybe in there grinding process... But I may own this barrel since before I noticed the "bend" I shortened the tang to barrel fit to .453. So I may have to live with this.. I haven't started inletting the barrel yet, I hope for a winter build as time allows. Thanks again for your input. I may have to go through the same "pucker factor".
 
I think the bores on ML'ers are just too big to be able to see anything. If it was a .22 barrel you might though. And, I would be careful about putting a steel rod in the bore too. It might be harder steel than the bore, and do some permanent damage, particularly if it gets stuck and has to be forced out. You could probably coat it or wrap it with tape and be ok though.

Bending them isn't that hard, but it takes a fair amount of oomph applied. If you have woodworkers vices on your bench take a couple of 2"x2" boards (a rigid hardwood like oak is best) and put them upright in the vice about 6"-8" apart. Put the barrel in between and then start pushing on the long end. It will take a surprising amount of force to get it to take a set. You can actually feel it yield when it moves enough to make the bend permanent. There are of course other ways, but that's the method I used.

You tube can be very helpful to see how it's done too. I remember watching one from the Springfield factory when they were making Garand barrels. They used a big wheel with a force multiplier on it and just cranked it down. Then looked down the barrel to see if it looked ok. It was surprisingly crude, but it seemed to work.

Just the same I would call Colerain or the people you bought it from though. If they're reputable, they will likely work with you and stand behind it even though you already fiddled with the tang some.
 
You shouldn’t be stuck with a bent barrel. I would contact Colerain. Of course it could have gotten bent in shipping. I have a light smoothbore barrel that got bent 3/8” in shipping because it was poorly packaged. A friend straightened it in 5 minutes. I couldn’t watch.
 
Thanks Col, Yeah I checked with a straight-edge after I noticed the discrepancy, and that confirmed my eye. Measuring the gap from the "waist" of the swamped barrel to the straight-edge: left side .031, right side .078 That's a 5/64 difference! But looking through the bore at a white paper, My eye doesn't detect a bend. I should check with Colerain. Maybe in there grinding process... But I may own this barrel since before I noticed the "bend" I shortened the tang to barrel fit to .453. So I may have to live with this.. I haven't started inletting the barrel yet, I hope for a winter build as time allows. Thanks again for your input. I may have to go through the same "pucker factor".
I doubt the bore itself is not straight, unless maybe the shipping packaging was obviously damaged when you received it. As I understand it, most barrel makers today drill the bore through the barrel blank first, then machine the outer profile with the barrel held between centers. If something is actually wrong, based on your description, it is likely the outside profile of the barrel was not machined correctly, if I had to guess. Bending the outside profile ‘straight’ on a swamped barrel in that case would result in a bent bore. As you don’t seem to have the equipment or the technical knowledge to confirm it is straight or not straight now, how will you confirm it is straight after ‘bending it straight’?

Call Colerain. Very unfair to them to discuss an issue like this on an open forum before you even talk to them. Let them correct an problem with their product. I had an issue with a barrel from another manufacturer. Called them, told them what I was measuring, returned the barrel to them, and they confirmed my findings. Had a new barrel in my hands about a week after I put the original in the mail. Postage covered both ways, and they include some goodies in the package for the inconvenience.

Call Colerain. 814-632-7513.
 
A good way to see if the bore is crooked or the barrel is actually bent is to mount it in the head stock of a lathe, Try to dial indicate both ends on the bore. If you can dial it in then revolve it at low RPM and look through the bore. it may look like a jump rope viewing through the bore. Barrels can be physically bent, have the swamp milled out of uniformity, the hole bored either tangentially out of concentric or I believe they can be bored in a serpentine out of concentric.
A perfectly straight and concentric bore is an accident as most are not.
Bent barrels should be straightened and then re- normalized to remove the bend stress in the steel as they will occasionally walk when heated up. Even a muzzle loader will heat up on a very hot day of match shooting.
 
Thanks Dave, I tried your simple suggestion of just looking down the barrel at a white surface, and it looks straight. I had been looking through the bore at bright light, or outside in the daylight, and that wasn't as clear. So that was helpful. I couldn't detect any noticeable run out in either breech or bore, but I should break down and buy a vernier caliper.... I'll talk to Colerain and get their imput. I don't have a laser or straight steel rod of the appropriate size around, but I can check with friends. Thanks again.
I doubt the bore itself is not straight, unless maybe the shipping packaging was obviously damaged when you received it. As I understand it, most barrel makers today drill the bore through the barrel blank first, then machine the outer profile with the barrel held between centers. If something is actually wrong, based on your description, it is likely the outside profile of the barrel was not machined correctly, if I had to guess. Bending the outside profile ‘straight’ on a swamped barrel in that case would result in a bent bore. As you don’t seem to have the equipment or the technical knowledge to confirm it is straight or not straight now, how will you confirm it is straight after ‘bending it straight’?

Call Colerain. Very unfair to them to discuss an issue like this on an open forum before you even talk to them. Let them correct an problem with their product. I had an issue with a barrel from another manufacturer. Called them, told them what I was measuring, returned the barrel to them, and they confirmed my findings. Had a new barrel in my hands about a week after I put the original in the mail. Postage covered both ways, and they include some goodies in the package for the inconvenience.

Call Colerain. 814-632-7513.
I doubt the bore itself is not straight, unless maybe the shipping packaging was obviously damaged when you received it. As I understand it, most barrel makers today drill the bore through the barrel blank first, then machine the outer profile with the barrel held between centers. If something is actually wrong, based on your description, it is likely the outside profile of the barrel was not machined correctly, if I had to guess. Bending the outside profile ‘straight’ on a swamped barrel in that case would result in a bent bore. As you don’t seem to have the equipment or the technical knowledge to confirm it is straight or not straight now, how will you confirm it is straight after ‘bending it straight’?

Call Colerain. Very unfair to them to discuss an issue like this on an open forum before you even talk to them. Let them correct an problem with their product. I had an issue with a barrel from another manufacturer. Called them, told them what I was measuring, returned the barrel to them, and they confirmed my findings. Had a new barrel in my hands about a week after I put the original in the mail. Postage covered both ways, and they include some goodies in the package for the inconvenience.

Call Colerain. 814-632-7513.
Thanks SDF, Yeah, maybe I went about this backward, and should have called Colerain first. I didn't intent to bad mouth them in any way, just thought my concern could be settled through some confirmation of bore straightness, and some more relevant information before contacting them. I wasn't griping, just looking for suggestions, but shouldn't have included their name, as the impression of dirt may stick with some. A learning for me, as a first time forum writer. Also, I wouldn't try to straighten a swamped barrel whose inner bore might be straight. Good to hear of your very favorable experience with Colerain, and I will communicate accordingly.
 
I think the bores on ML'ers are just too big to be able to see anything. If it was a .22 barrel you might though. And, I would be careful about putting a steel rod in the bore too. It might be harder steel than the bore, and do some permanent damage, particularly if it gets stuck and has to be forced out. You could probably coat it or wrap it with tape and be ok though.

Bending them isn't that hard, but it takes a fair amount of oomph applied. If you have woodworkers vices on your bench take a couple of 2"x2" boards (a rigid hardwood like oak is best) and put them upright in the vice about 6"-8" apart. Put the barrel in between and then start pushing on the long end. It will take a surprising amount of force to get it to take a set. You can actually feel it yield when it moves enough to make the bend permanent. There are of course other ways, but that's the method I used.

You tube can be very helpful to see how it's done too. I remember watching one from the Springfield factory when they were making Garand barrels. They used a big wheel with a force multiplier on it and just cranked it down. Then looked down the barrel to see if it looked ok. It was surprisingly crude, but it seemed to work.

Just the same I would call Colerain or the people you bought it from though. If they're reputable, they will likely work with you and stand behind it even though you already fiddled with the tang some.
Thanks Col. for the bending advice, and I will call Colerain for their input- Not fair for me even bring up their name as I am working and learning through this question
 
A good way to see if the bore is crooked or the barrel is actually bent is to mount it in the head stock of a lathe, Try to dial indicate both ends on the bore. If you can dial it in then revolve it at low RPM and look through the bore. it may look like a jump rope viewing through the bore. Barrels can be physically bent, have the swamp milled out of uniformity, the hole bored either tangentially out of concentric or I believe they can be bored in a serpentine out of concentric.
A perfectly straight and concentric bore is an accident as most are not.
Bent barrels should be straightened and then re- normalized to remove the bend stress in the steel as they will occasionally walk when heated up. Even a muzzle loader will heat up on a very hot day of match shooting.
Good idea, my son-in-law has a machine shop and could probably do this for me. I should of thought of him earlier... Thanks
 
I don't know if this would work, I never tried it, just read about it. The old time barrel makers would check their bores for straightness with a string and a willow bow. Drop a string down the bore , tie each end to a flexible willow sapling pulled into the shape of a bow. hold barrel to the light and slowly rotate it to check for straightness.Bend as needed.The simple ways and injunity of the old time gun makers always amazes me. The modern day equivalent of a willow bow would be a piece of 1/2 hot water PVC.pipe. It worked for them I'd try it if the need ever arose.
 
Hers the thing..... if your flats are that far off, either the barrel is bent, or the barrel was milled improperly.
The only solution is the bend the barrel straight.
This will fix either one, or both.
Please don’t do this till it’s sighted in, or you may have to do it again.
Colerain should honor a return, if you’ve only messed with the breechplug.
 
Hers the thing..... if your flats are that far off, either the barrel is bent, or the barrel was milled improperly.
The only solution is the bend the barrel straight.
This will fix either one, or both.
Please don’t do this till it’s sighted in, or you may have to do it again.
Colerain should honor a return, if you’ve only messed with the breechplug.
How on earth would ‘bend the barrel straight’ work if the bore is already straight and it is milled incorrectly? Bend the outside you also bend the bore......
 
I guess I misunderstood the issue. I assumed if the outside was off, the bore was as well. That being the case, it would fix both. If it’s that far off, I’d send it back, regardless of whether I’d modified it or not.
 
Using the string and bow to check the straighteners of the bore is simple and works. You can also hold the unbreached barrel up to a light, or the sky, and look down the bore. You will see circles in the bore and if they are all concentric the bore is good. If it is bent you will see non concentric circles at the point of the bend.
 
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