Bending airgun barrels: Part 3
by Tom Gaylord, a.k.a. B.B. Pelletier
This report talks about bending and straightening airgun barrels. Sometimes, airgun barrels are bent and need to be straightened to work properly with their sights. While there are many home fixes for doing this, I wanted something more precise that I could control more closely.
Today is the beginning of a very large 2-part report that’s nestled within this larger ongoing article. There is too much information to get into a single day’s report, yet everything should stay together, so I am running it sequentially over the next two days.
I am about show you the barrel straightening/bending fixture I built and will describe how it works. Then, I’ll show the results of using it.
In the last report, I tested a breakbarrel that had been fired with the barrel open. The barrel was bent up, so with the scope adjusted as low as it would go, the gun still shot about 9 inches too high at 10 meters. Obviously, that’s way too far out of the range that the scope’s adjustments can accommodate, so something had to be done.
Let me show you my simple barrel-bending fixture. I built it in 20 minutes at no cost; but even if you had to buy everything, you’d still spend less than $20. Actually, you would probably spend less than $10 for this fixture. Once I show you how it works, you’ll probably see all sorts of ways to improve it and further reduce the cost.
The fixture is a plank with a 4″x4″ post of oak lumber attached to it horizontally with wood screws. The base was made from a 1-inch pine plank that’s 12″ wide by 19″ long. The length isn’t that important, but I think I got it right for my needs. I made the 4×4 wood post a little shorter than the base for no particular reason.
I attached my 4×4 oak post to the base with 8 wood screws. These were 2.5″ long, but all I cared about was making their heads flush on the bottom of the base and ensuring that the screws didn’t come though the post on the other side. The oak post was left over from a pallet I disassembled years ago to make a workbench. It isn’t good wood, but it served the purpose I needed perfectly. The only reason for the post is to give a clamp something to bear against. I do think hardwood is best for this application, though pine would probably also work.
This is the barrel-bending fixture. The darker wood post at the top is a 4″x4″ oak post cut from a pallet. There are three small wooden blocks cut from 1″x3″ lumber. You’ll see how these are used in the next picture. There’s also a piece of thick leather belt that I used to keep the clamp from scratching the barrel when I pressed directly against it. And the clamp is a Craftsman 6″(150mm) c-clamp.
Barrel bending fixture in operation.
The above picture shows everything. The top of the barrel is supported by two wooden blocks, and the clamp pushes up from the bottom. When the clamp is tightened, the barrel will bend down. By allowing the clamp to flip on its side and contact the post, all sideways movement stops and the pressure stays in a straight line.
As you can see, the wood post is under no sideways pressure from the clamp. The base isn’t even required! I just put it there to keep the post up off the surface of whatever table I was working on.
The gun extends to the right, out of the picture. It’s laying on clean rags to elevate it to the same level as the barrel and to keep it still. The scope is still mounted on the gun, so I can take the rifle from the clamp and test-fire it immediately after a bend.
Problem with the clamp
After I’d tightened the clamp as far as I could, the barrel still was not bent enough — so I used a 6″ cheater bar to extend the clamp pin for better leverage. With the extra leverage, it was possible to bend the barrel much more so the bend was visible.
Here the barrel is really bent. Even with this much of a bend in it, however, it still sprung back to almost where it had been. I’m using a lead ingot here instead of a wood block for pressing on the barrel.
Don’t let anyone tell you that airgun barrels bend easily, because they don’t! They also spring back after the pressure is released, so even when they appear to be bent in the fixture, it probably won’t be enough at first.
I took the rifle from the fixture and fired it at 10 meters, as before. You’ll remember that it was shooting 9″ high after the barrel was initially bent by firing the gun with the barrel open — and that was with the scope adjusted as low as it would go.
This time, after the first bend made in the fixture, the rifle shot about 4″ high at the same 10 meters. I was getting somewhere, but had more to do because the scope was still adjusted as low as it would go and the gun still shot high.
The scope was centered on the aim point for all shots in this picture, and the pellets shot after the first bend struck about 4″ high at 10 meters. I’d eliminated over half the bend in the barrel with the first use of the fixture.
I put the rifle back in the fixture and bent the barrel again. This time, I had to use even more effort to get the barrel to bend — so much more, in fact, that I bent the handle on the c-clamp. I would have to use something else to apply pressure in the future.
With the cheater bar, I applied too much force to the c-clamp handle and bent it. That’s the end of using this clamp.
The second bend lowered the shots only about a half-inch. The barrel had to be bent more, and I needed a new c-clamp or something else to apply pressure.
I was frustrated at this point, so I stuck the barrel in the bottom space of my workbench and applied corrective bending pressure with my weight, alone. This is the way others say they bend airgun barrels. I found it very difficult to control what I was doing this way, and I had to apply as much force as my weight permitted — but the barrel did continue to bend. The next picture tells the rest of the story.
This target was fired with the center of the lower bull being the aim point for all shots. The single high shot is a confirmation shot from after the second bend. Then, using the leverage of the workbench, I bent the barrel a third time and got the rise of the pellet down to about 2.25 inches above the aim point.
Back to the workbench I went, bending the barrel a 4th and 5th time. You can see the progression of the groups as they drop closer to the aim point after each bend. The problem was that I wasn’t controlling the bend like I wanted, so this was all guesswork. It went fast enough, because the gun could be shot immediately after each bend. But I couldn’t see what I was doing as I did it.
You can see the results of the 4th and 5th bends. By the 5th bend, the groups were landing just 1″ to 1.25″ high at 10 meters. But the scope was still adjusted as low as it would go, so more adjustment (of the barrel) was needed.
More to come
As you can see, I really put in the time on this test! There’s a happy ending coming, but I need another full report to get to it.
At this point in the exercise, the barrel was much closer to where it needed to be, but I had lost the use of my c-clamp…and with it, I lost the control I wanted to have. I now know that airgun barrels can be bent, and it doesn’t take that much equipment to do it. But bending them with leverage, alone, is too crude a method for me. I want some control over the process.
Tomorrow, I’ll finish this report and will show you a solution that works quite well.