Barrel bending

[josh3rd]

I would be hesitant to attempt barrel bending, but it certainly can be done successfully.

Believe it or not, this is an actual target pistol.

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I have heard this was an advertising piece. I have also heard that it was done to have a longer barrel while keeping the over all length to a specific dimension. Both of the articles I had seen described the pistol as very accurate. I can't find either anymore.

Darn Lewis, I heard the same thing about that pistol but honestly they haven't sold me on it yet, lol. thanks for your feedback/input brother

 

[josh3rd]

If we quit calling it "BARREL BENDING" and started calling it "BARREL ADJUSTING" instead I think it would be a lot more accurate and less eyebrow-raising description of what is actually happening.

I honestly don't think anyones eyebrow's raising anymore than usual. plus in all of my searching, "barrel adjusting" is no where to be seen/found. So i think barrel bending is the winner...well at least in my post, lol

 

[r1lover]

If I don't get any response to this I am going to repost my question because I'd really like to know; how far do you need to bend a barrel before you see results in your POI?

I once tried to change my POI by bending a barrel without success. I made a fixture out of heavy 3 inch channel iron the length of the barrel. I drilled a hole of similar diameter as the barrel through a piece of 2x4, then cut the 2x4 in half so I had two pieces of wood to cradle the breach and muzzle ends of the barrel in and taped the wood to each end of the channel iron. I drilled a hole through the center of the channel iron and inserted a LARGE eye bolt with a nut on the other end.

I put the barrel through the eye bolt and cradled the barrel ends in the half pieces of wood. I slipped a short piece of wood between the point of contact between the barrel and eye bolt to prevent damage to the barrel and proceeded to tighten the nut on the eye bolt, putting a bend in the barrel. I started very small, noticing the barrel simply sprung back to its original shape each time I loosened the nut on the eye bolt. Eventually I tightened the nut enough to put an INCH of deflection in the barrel and the barrel still sprung back to its original shape. At this point I feared that all of a sudden the steel in the barrel might yield under pressure and I'd get a tremendous permanent bend and ruin the barrel so I quit.

I wish I had taken a picture of this but I didn't.

Thoughts?

 

[AirShot]

Yep...you nust keep going a little at a time until it gives a little. No precise way to do it!! Even in my full machine shop with all kinds of fancy equipment, it just takes patience and time...trial and error....

 

[josh3rd]

Yep...you nust keep going a little at a time until it gives a little. No precise way to do it!! Even in my full machine shop with all kinds of fancy equipment, it just takes patience and time...trial and error....

x2

 

[nervoustrig]

Eventually I tightened the nut enough to put an INCH of deflection in the barrel and the barrel still sprung back to its original shape. At this point I feared that all of a sudden the steel in the barrel might yield under pressure and I'd get a tremendous permanent bend and ruin the barrel so I quit.

Technically that is what you are trying to achieve. The steel has to yield. In other words, move beyond the point of elasticity (recovers to its original shape) to the point it yields and permanently changes shape. 

How much force is needed? How much deflection?

As much as it takes Like Airshot said, the only practical approach is trial and error. Work your way up gradually until it begins to undergo a permanent change. A very slight change makes a big difference. For example, moving the muzzle by the thickness of a credit card will change the POI by about 1.5 inch at 25 yards.

 

[MP44]

Ross Seyfried wrote an airgun article back in the early 90s. In the article, it mentions factory employees ( HW or Diana ) bending barrels to line up poi with the sights centered.

 

[r1lover]

Thanks for the answers so far!

Nervoustrig, yes, yield is exactly correct. I am not a machinist or metallurgist but I am an engineer which probably makes me dangerous, lol!

I feared the difference between "no yield" and "yield" might be similar to the difference between static and dynamic coefficients of friction where one is greater than the other and once something breaks loose and starts to move it REALLY starts to move. I imagined my barrel suddenly "yielding" a whole lot instead of just a little.

 

[AirShot]

The real key is finding a way to see how much it actually moved. This is where my shop had an advantage. It only takes a very small bend to make the adjustment, mabey to small to see with the naked eye!!! Yep...you need to keep reassembling your rifle to know for sure if it moved. I had benefit of having a way to mount the breech block to hold it in the same position each time so I could measure the amount of bend that actually took place. Still had no control on how much to bend !! Watched a guy bend his in the crotch of a tree, probably put it together and apart at least a dozen times before he got it right...it is not rocket science unfortunately!!!!

 

[nervoustrig]

I feared the difference between "no yield" and "yield" might be similar to the difference between static and dynamic coefficients of friction where one is greater than the other and once something breaks loose and starts to move it REALLY starts to move. I imagined my barrel suddenly "yielding" a whole lot instead of just a little.

Gotcha, yeah it’s a more gradual thing. You’d have to go way overboard to reach the point where it would suddenly fold. 

Since you are an engineer, it might be useful to look at a stress/strain curve for mild steel.


Take note of the point labeled “yield strength”. That’s the level we’re wanting to exceed by just a bit.

And note that beyond it in the y axis (stress) there is still some distance before reaching the material’s ultimate strength…meaning you’d have to continue increasing the load quite a bit before it would reach a tipping point and suddenly become easier to bend and just fold over. Meanwhile the x axis (strain) tells us it would have undergone quite a bit of deformation by the time it reached that point…about 2x as much as it moved to get to the yield point in the first place.

 

[r1lover]

Nervoustrig,

Right. So on the graph you provided my worry occurs between the upper yield point B and lower yield point C, where elastic distortion turns to plastic distortion. My understanding is once the crystal bonds begin to break the stress needed for their motion drops abruptly and plastic distortion can occur quickly in mild steel. I feared that at some point while turning the nut and adding another 0.05 inches of deflection in the barrel would suddenly result in 0.1 inches of permanent plastic distortion.

My situation is I purchased a used break barrel I knew nothing about. The POI is high which led me to believe maybe the barrel had been allowed to snap shut at some time, but laying the barrel along a straight edge there is no indication of a bend unless it is at the barrel/block junction and I cannot see it. It could be my imagination, but visually it almost appears the bore is not straight.

In any case, the safest solution is probably a droop mount installed backwards with the recoil arresting pin relocated into a new hole drilled in the other end of the mount.

It amazes me that anyone can bend a barrel an appropriate amount using the crotch of a tree or car bumper, lol!

ChrisK

 

[thumper]

Nervoustrig,

Right. So on the graph you provided my worry occurs between the upper yield point B and lower yield point C, where elastic distortion turns to plastic distortion. My understanding is once the crystal bonds begin to break the stress needed for their motion drops abruptly and plastic distortion can occur quickly in mild steel. I feared that at some point while turning the nut and adding another 0.05 inches of deflection in the barrel would suddenly result in 0.1 inches of permanent plastic distortion.

My situation is I purchased a used break barrel I knew nothing about. The POI is high which led me to believe maybe the barrel had been allowed to snap shut at some time, but laying the barrel along a straight edge there is no indication of a bend unless it is at the barrel/block junction and I cannot see it. It could be my imagination, but visually it almost appears the bore is not straight.

In any case, the safest solution is probably a droop mount installed backwards with the recoil arresting pin relocated into a new hole drilled in the other end of the mount.

It amazes me that anyone can bend a barrel an appropriate amount using the crotch of a tree or car bumper, lol!

ChrisK

You're issue was that you made the elaborate fixture to bend it, and you couldn't feel it move. Also you were putting all the force in one spot, right where the eye bolt was.

And the barrel may be straight to within .0015" and the issue with the angle of the breech block in relation to the barrel.

I don't know how you put "OK I can feel it give a little now" in a graph, but that's usually "just right" for the first adjustment LOL

I put the breech block in a big-ass bench vise, and pull on the muzzle end. You can feel when the flex stops, and the barrel "bends". Also I like to think that the bend isn't centralized in one spot this way.

As for weakening the steel I can't see how that's even a feasible concern. I took my brand new HW50S out of the box, handed it to my dad, and he immediately let the barrel slip and it slammed shut bending the barrel skyward. Looked absolutely ruined. I took it apart, bent it back, and it's the most accurate breakbarrel I've owned and it's been shot many thousand times with no change. Again, not scientific with a graph, but I think that's about as "worst-case" as it gets in real life. 

I've done breakbarrels and underlevers and never had one shoot anything but better afterwards. I've even done three FWB300 actions.

Either way, just pull the barrel off, put the breech in a vise or under a car tire or whatever, and pull it till it points where you want it to go and life will be grand.

 

[gonzav71]

Here is a link to a step-by-step barrel bending blog post by Tom Gaylord

Bending airgun barrels: Part 5 | Pyramyd Air Gun Blog

 

[josh3rd]

Nervoustrig,

Right. So on the graph you provided my worry occurs between the upper yield point B and lower yield point C, where elastic distortion turns to plastic distortion. My understanding is once the crystal bonds begin to break the stress needed for their motion drops abruptly and plastic distortion can occur quickly in mild steel. I feared that at some point while turning the nut and adding another 0.05 inches of deflection in the barrel would suddenly result in 0.1 inches of permanent plastic distortion.

My situation is I purchased a used break barrel I knew nothing about. The POI is high which led me to believe maybe the barrel had been allowed to snap shut at some time, but laying the barrel along a straight edge there is no indication of a bend unless it is at the barrel/block junction and I cannot see it. It could be my imagination, but visually it almost appears the bore is not straight.

In any case, the safest solution is probably a droop mount installed backwards with the recoil arresting pin relocated into a new hole drilled in the other end of the mount.

It amazes me that anyone can bend a barrel an appropriate amount using the crotch of a tree or car bumper, lol!

ChrisK

You're issue was that you made the elaborate fixture to bend it, and you couldn't feel it move. Also you were putting all the force in one spot, right where the eye bolt was.

And the barrel may be straight to within .0015" and the issue with the angle of the breech block in relation to the barrel.

I don't know how you put "OK I can feel it give a little now" in a graph, but that's usually "just right" for the first adjustment LOL

I put the breech block in a big-ass bench vise, and pull on the muzzle end. You can feel when the flex stops, and the barrel "bends". Also I like to think that the bend isn't centralized in one spot this way.

As for weakening the steel I can't see how that's even a feasible concern. I took my brand new HW50S out of the box, handed it to my dad, and he immediately let the barrel slip and it slammed shut bending the barrel skyward. Looked absolutely ruined. I took it apart, bent it back, and it's the most accurate breakbarrel I've owned and it's been shot many thousand times with no change. Again, not scientific with a graph, but I think that's about as "worst-case" as it gets in real life. 

I've done breakbarrels and underlevers and never had one shoot anything but better afterwards. I've even done three FWB300 actions.

Either way, just pull the barrel off, put the breech in a vise or under a car tire or whatever, and pull it till it points where you want it to go and life will be grand.

Thumper,



It's more likely laziness on my part. I hate to have to take it apart, then go to my trailer hitch, bend it or what i had thought was bent enough, assemble it back, take a few shots to only see it's poi moved on 1/4" when i need say 1.5", lol. I wish I had a table vice. quick question, will a table vise be sturdy enough on a heavily made picnic table?

 

[nervoustrig]

I wish I had a table vice. quick question, will a table vise be sturdy enough on a heavily made picnic table?

My workbench weighs about 200lbs and a broad footprint. The first time I went to tweak a barrel, my pushing motion lifted the near side of the bench. No problem, I'll use a jerking motion instead so I'm attempting to torque the far side of the table off the floor. When that side also lifted, I bolted the bench to the floor. That did the trick.

 

[thumper]

Nervoustrig,

Right. So on the graph you provided my worry occurs between the upper yield point B and lower yield point C, where elastic distortion turns to plastic distortion. My understanding is once the crystal bonds begin to break the stress needed for their motion drops abruptly and plastic distortion can occur quickly in mild steel. I feared that at some point while turning the nut and adding another 0.05 inches of deflection in the barrel would suddenly result in 0.1 inches of permanent plastic distortion.

My situation is I purchased a used break barrel I knew nothing about. The POI is high which led me to believe maybe the barrel had been allowed to snap shut at some time, but laying the barrel along a straight edge there is no indication of a bend unless it is at the barrel/block junction and I cannot see it. It could be my imagination, but visually it almost appears the bore is not straight.

In any case, the safest solution is probably a droop mount installed backwards with the recoil arresting pin relocated into a new hole drilled in the other end of the mount.

It amazes me that anyone can bend a barrel an appropriate amount using the crotch of a tree or car bumper, lol!

ChrisK

You're issue was that you made the elaborate fixture to bend it, and you couldn't feel it move. Also you were putting all the force in one spot, right where the eye bolt was.

And the barrel may be straight to within .0015" and the issue with the angle of the breech block in relation to the barrel.

I don't know how you put "OK I can feel it give a little now" in a graph, but that's usually "just right" for the first adjustment LOL

I put the breech block in a big-ass bench vise, and pull on the muzzle end. You can feel when the flex stops, and the barrel "bends". Also I like to think that the bend isn't centralized in one spot this way.

As for weakening the steel I can't see how that's even a feasible concern. I took my brand new HW50S out of the box, handed it to my dad, and he immediately let the barrel slip and it slammed shut bending the barrel skyward. Looked absolutely ruined. I took it apart, bent it back, and it's the most accurate breakbarrel I've owned and it's been shot many thousand times with no change. Again, not scientific with a graph, but I think that's about as "worst-case" as it gets in real life. 

I've done breakbarrels and underlevers and never had one shoot anything but better afterwards. I've even done three FWB300 actions.

Either way, just pull the barrel off, put the breech in a vise or under a car tire or whatever, and pull it till it points where you want it to go and life will be grand.

Thumper,



It's more likely laziness on my part. I hate to have to take it apart, then go to my trailer hitch, bend it or what i had thought was bent enough, assemble it back, take a few shots to only see it's poi moved on 1/4" when i need say 1.5", lol. I wish I had a table vice. quick question, will a table vise be sturdy enough on a heavily made picnic table?

I dont know what my bench weighs, but it's made from 4X4 lumber and is loaded with Toyota differentials and early Bronco parts LOL. Pretty heavy and it tries to move a bit. I'm light and agile and a little scrawny fella anyway so I just put my foot against the side of the bench to pull and it goes fine. 

A picnic table has a real wide footprint. I doubt it would move too much if you mounted the vise sturdy to it. If it does just throw some burgers on it and have a few friends park their butts on it

Or you could mount it sideways on a fencepost, or even a tree if need be. 

If you have a trailer hitch with a 2" receiver, which I assume is what you're using, a vise mounted on a spare receiver is a HANDY thing to have and will solve your problems! I have one stashed around here somewhere.

On that note, a Weihrauch breech block might fit inside a 2" receiver. Stick it in there horizontally and pull sideways and you might be onto something. Just spitballing there...

Another thought if you are doing it with the gun together, is use a cheap boresight laser and "zero" the scope with it before you start, and then check it afterwards for a rough idea how far you went. I had one at one time and it was handy to have. The batteries went dead and I stashed it somewhere and haven't seen it since......I should probably buy another one.

I've always just had a big vise and table and 20 ton press since it was necessary for other stuff I work on. Otherwise I'd be improvising too. Don't get the idea I did all this just for bending barrels!

Last hairbrained idea if you don't have a vise, is to bolt a couple blocks of wood to the leg or anywhere on the table or something sturdy that would fit against the sides of the breech block. One on top and bottom, and just pull up. Easy and cheap and removable when you're done. 

 

[Bear-of-Grayling]

Back in a 80’/90’s Weihrauch (maybe Beeman) was marking the gun gun box “scope angle or barrel angle” forgot which. These particular rifles were inspected and found to have the least amount of barrel drop. They were recommended for scope usage. It seems to me that if Weihrauch could have simply manipulated the barrels by bending them in line, they surely went through a lot of trouble inspecting and labeling the box while making their products look inferior. 

 

[nervoustrig]

It seems to me that if Weihrauch could have simply manipulated the barrels by bending them in line, they surely went through a lot of trouble inspecting and labeling the box while making their products look inferior.

Seems like that represents the easy way out for the manufacturer. Surely a measurement is much quicker and easier than compensating for the angle...which would then need to be measured or verified in some way, adding still more time to the manufacturing process.

 

[thumper]

Back in a 80’/90’s Weihrauch (maybe Beeman) was marking the gun gun box “scope angle or barrel angle” forgot which. These particular rifles were inspected and found to have the least amount of barrel drop. They were recommended for scope usage. It seems to me that if Weihrauch could have simply manipulated the barrels by bending them in line, they surely went through a lot of trouble inspecting and labeling the box while making their products look inferior.

Or, that Dr Beeman being the "salesman" he was, simply found a way to get a few more bucks out of the customer. 

Cause let's face it, how do you know you actually got a select barrel angle? What if the gun beside it had an even more select barrel angle and got tossed in a box that wasn't marked or upcharged? Or more likely, what if they just all got marked "scope angle" and an extra $3 was added to the price? 

Or what if Beeman took the gun out of the box and stuck the muzzle in a hole in the wall and gave it a swift bend, lol. 

The only thing we are sure of is that Beeman was a helluva "salesman" to put it lightly....

 

[218bee]

Recently bought a nice R10 in .20 that had a barrel with a noticeable downward bend. Removed it, placed the block in a padded vise, and bent it by hand, back to where it was visually straight. Full disclosure, it was my first time and it took three or four attempts, but when reassembled, its the most accurate Springer I own. Just go slow and dont have any distractions.