Bending airgun barrels: Part 2

by B.B. Pelletier

Part 1

This is the second part in our series of bending airgun barrels.

Settle in, boys and girls, for this report will be long and involved. Today, I’ll begin the quest to bend or straighten an airgun barrel to fix many problems.

I’ve waited to do this report until I could give you a barrel bending (straightening) fixture that anyone could build for very little money. I’ve not built mine yet, but the design is so simple that I have complete faith it will work. And if it doesn’t, there’s always the crotch of a tree or the joint in a picnic table that’s currently being used by many people to do the same thing. I think my fixture gives you a lot more control over the process, so let’s see if it works.

First, we need a bent barrel. I intentionally bent an airgun barrel for you. I bent a breakbarrel by firing the gun with the barrel broken open, as in the common excuse –”My hands slipped while I was cocking the gun!” (everyone who ever did this uses that excuse).

The gun I’m working with is already marked for destruction. I thought that before it goes away, it might serve one last honorable duty. It’s a .22-caliber rifle and I selected .22-caliber RWS Hobby pellets for this test. We don’t care about accuracy in this test — just where the pellets are landing with respect to the scope setting. Don’t ask what kind of gun it is — the model is unimportant. I removed the anti-beartrap device so the barrel would close when the trigger was pulled, so this rifle was initially safe as it was designed and built, but I circumvented it.

I first photographed the gun with an obsolete CenterPoint Optics 3-9×40 AO scope mounted. CenterPoint scopes are no longer made by Leapers, so this scope is now unavailable, but it has a mil-dot reticle that became important in today’s test.


Here’s the test rifle with its scope mounted. This is before the first shooting test.

First thing
The first thing was to establish that the rifle could hit the target using the test scope. I chose to use 10 meters for the test distance; because at 25 yards, with the way the pellet would rise after the barrel was bent, I could wind up with more holes in the walls of the house. Edith tells me that’s a bad thing!

The first shot was from 15 feet. I shot in the standing position and supported my hand with the door jamb of the garage door. Because I’ve rearranged my garage, I have to sight-in at 15 feet instead of the old 10 feet. I shot at the upper bull on the target, and the pellet hit just below the lower bull. The rifle was striking the target about 3-1/4 inches below the point of aim at 15 feet. Then, I backed up to 10 meters and shot again.

At the 10-meter bench with the same scope setting, I shot at the top bull again. A three-shot group was low and to the left of the aim point. It was not as low as it was at 15 feet, which is to be expected. So, I adjusted the scope up and to the right to correct it.

The first shot after the scope was adjusted was at the lower bull. The pellet landed a half-inch low and a quarter-inch to the left of the aim point. A second scope adjustment put the next pellet into the center of the targeted bull. Four more shots completed a 5-shot group.

The picture that follows documents everything you’ve just read.


The first target describes how the rifle was initially sighted in. The tight group in the lower bull was the final result for five Hobbys at 10 meters.

I then took the scope off the rifle before bending the barrel. This is a very stressful procedure, and there’s no reason to subject the scope to this kind of punishment. However, this is a place where bias can enter my test, because taking the scope off the gun and remounting it again will definitely cause the aim point to shift some. I hope to show, however, that it moves so far upward that it cannot be blamed on just removing and remounting the scope, alone.

Bending the barrel
What I am about to describe is a way of definitely bending an airgun barrel. Don’t do it, because it can also break the stock. If your fingers are in the way when this is done, it’ll cut them off. I broke open the barrel until the gun was cocked, then pulled the trigger with the barrel in the open position. Remember that I had already removed the anti-beartrap mechanism, so now the gun would fire with the barrel in the open position.

The piston moving forward acts on the cocking link to slam the barrel shut so violently when the gun fires that the barrel bends upward every time. This is a classic abuse of an airgun. If I’m ever called as an expert witness in a liability case, I will say that this was done intentionally — because in every instance I’ve investigated, it was.

Now you can see the results of doing what I just described. The barrel is bent upward, starting at the end of the baseblock — a classic case of a slam-fire in a breakbarrel.


You can clearly see that the barrel has been bent upward in this photo.

The stock was not broken this time, but one of the two stock screws was pulled deeper into the wood on one side of the forearm. I can see the barrel is bent without looking for it, so I’m now very concerned that the gun will shoot above the target when I remount the scope.

Once the scope is back on the rifle, I return to 15 feet from the target — and this time, I drew a new aim point below the target at the bottom of the cardboard target backer. The same aim point was used for all shots in this part of the test.

Then I took that first shot. The pellet struck the target 4-3/4 inches above the aim point. I was on paper, so I cranked in all the down elevation adjustment the scope had, and the second pellet dropped about 2 inches below the first. It was still 2-3/4 inches high at 15 feet. I felt safe, so I backed up to 10 meters and shot off the bench.

The first shot from the bench landed 7-1/2 inches high at 10 meters. It was perilously close to the target clip that holds the target to the backstop, so I used the mil-dot above the crosshairs for the next 5 shots. I now had a group on paper at 10 meters, but it was so far above the aim point of the scope that it was completely useless. At 25 yards it would be many inches higher than it was here. So, the barrel is definitely bent upward and has to be dealt with before the gun can be used again.


This target documents how the same rifle shot after the barrel was bent. The aim point at the bottom proved not to be low enough when I backed up to 10 meters, so I had to use the first mil-dot above the crosshair intersection to hold on the aim point. I was aiming about 9 inches low at 10 meters — and was still almost off the top of the target!

Now, I have an airgun with a documented bent barrel on my hands. You absolutely cannot see the bend by looking through the barrel, as I’ve been told. At least I don’t see it. But the results on paper and even just looking at the gun tells me the barrel is definitely bent.

I have to straighten this barrel, obviously. My next step will be to build a barrel bending and straightening fixture that’s cheap and easy to make. I’ll use the fixture to straighten this barrel and show you the results of the job after I’m done.

After that, I have a BSF S70 rifle that currently shoots too high with the aftermarket peep sight that’s installed. If my barrel bending/straightening fixture works as expected, I will apply it to that gun and show the results.

The bottom line of this report will be a way for you guys to bend your barrels as required, with complete control and little risk of damage. I’m as new to this as are many of you, which is why I’m doing it for all of us.

45 thoughts on “Bending airgun barrels: Part 2

  1. The first thing was to establish that the rifle could hit the target using the test scope. I chose to use 10 meters for the test distance; because at 25 yards, with the way the pellet would rise after the barrel was bent, I could wind up with more holes in the walls of the house. Edith tells me that’s a bad thing!

    Maybe you should borrow from Holmes, and put her initials up in pock-marks.


  2. Question will you use a level for your BSF70.Will you rest riffle so spring chamber is level then use level on top of barrel so both of parts are level together.If you just bend barrel up enough to allighn front sight to rear sight then the point of aim will climbe up as farther and farther your targets are,but I may be wrong.


    • Chris,

      I have no plan to use a level. I figure nothing on the gun is parallel to anything else, so my eyeball should be the best tool in this case.

      When you see the fixture I build, I think you’ll see what I mean.

      B.B.


    • Chris,

      In my opinion, based on my experience bending barrels, the primary reason to bend a barrel is not to get it “level” with anything but rather have the poi (Point Of Impact) match your poa (Point Of Aim).

      Since the velocity of guns differ, sighting systems (open sights or scope) differ, range of adjustments on scopes vary, the guns preferred pellet weights differ, your personal zero range differs from gun to gun, etc. the barrel may end up “level”, pointing slightly downward or slightly upward. What good is a “level” barrel if it won’t shoot where you need it to is the point I’m struggling to make.

      Let’s not forget, adjustable scope mounts can usually compensate for this as well (though an unlikely option in the extreme case of a slam fire like is shown in todays article. Yuck.). Bending barrels is just another option.

      kevin


  3. B.B.

    There are a lot of guys complaining that they can’t adjust their scope far enough for 250 yd shooting. Looks like you invented the perfect solution….
    Zero at 10 yds, slam fire it, and PRESTO….an instant 250 yd zero. Another slam fire should take it out to 350.

    twotalon


    • TT,

      Oh, gosh! I hope people don’t start doping stupid things like that! I thought about that when I wrote this report, but I just cannot be responsible for all the world’s idiocy! I have trouble enough managing my own. ;)

      B.B.


  4. B.B.

    It really is a shame that you have to trash that rifle. That is a better 10 yd group than I have seen come out of way too many.

    twotalon







        • Unless you’ve found a set of scope mounts with spherical compression rings/inserts. The rings will be rather large (if you are lucky, no more than if you stuck a 1″ tube in a 30mm ring…

          Pity I can’t draw images here.

          The inserts would be something like nylon, maybe with friction tape on the flat side that bears against the tube. The outer surface would be convex curved. The inside of the metal rings would have a matching concave curve. As long as the metal rings in narrower (front to back) than the curve radius there would be free area on the ends to allow the inserts to tilt, matching the tube angle against the rings.


          • Wulfraed,

            Yes, your idea works very well.

            You’ve done a good job of describing Burris Signature Rings (for dovetails) and Burris Signature Zee Rings (for weaver). The Burris nylon? delrin? inserts come in various sizes and allow for adjustment of windage and/or elevation.

            kevin


  5. O.K. Rekord fans….
    I can feel some second stage travel on one of my rifles (compared to the other HWs). It has a fine dragging feel (no distinct bumps).
    My instincts tell me to add more moly, and to crank the front screw (torx) in a bit. Does this sound right ? Maybe polish the first sear a bit ?

    twotalon


    • TT,

      Want to polish air? There is no first sear.

      What you have in a Rekord is a trigger that moves across the sear and stops at one point. That marks the second stage.

      Screw 51B in the diagram shows the sear contact adjustment.

      Moly won’t make a big difference here, but a proper adjustment will make it break like glass.

      B.B.


      • Terminology error. I meant the end of the tongue which holds the sear lock which holds the sear for the piston rod. Still looks like 3 sears to me.

        I put some moly on the end of the tongue. Still feel travel, but completely smooth.
        There is about 1/16 inch travel at the end of the trigger blade between the beginning of the second stage and firing (everything lets go of everything).

        twotalon


  6. BB,

    I find that I can see even a slight bend by looking through the bore. It’s a matter of having the right light intensity. I can see concentric reflections down the bore and I see where the reflections deviate from being concentric. With practice, you can even tell about where the center of the bend is in relation to the length of the barrel. You can also see whether it’s a sharp bend or a gentle banana curve like you’ve created here.

    /Dave



      • Time to find the laser safety goggles, and a well collimated/narrow-beam laser pointer. (and some long arms?)

        View from the breach while aiming the laser down the muzzle, and see how far you get before the beam starts being cut off by the inside curve of the bend…

        {of course, one’s safety goggles have to be the proper color to block the laser… My reddish goggles would pass a red pointer like nothing; they were supplied to reduce damages from a green Wicked Lasers product [I’d love to get one of their newer ones with the built-in cooling — mine is only rated for something like 30 seconds out of each two minutes or so; but it will “cut” black vinyl electrical tape}


      • I see. That would make it difficult. All the light gets absorbed in the barrel. Maybe we can use this process for treating telescope walls to reduce scattered light! :-)

        Interesting that such a horrible barrel would give you semi-decent groups! I’ve heard of it before, but it’s usually a rarity.


  7. Just stick with the open sights and you’ll be fine, right :)? Looking forward to the rest of the reports, as I think my 36-2 may have slight droop; can’t remember exactly because it has literally been years since I had a scope on it.

    Shame to have to destroy that air rifle — looks interesting; I have some guesses on its origins, but I’ll keep them to myself.


    • BG_Farmer,

      Open sights no working is what drove this entire report! I have this BSF S70 with a rear peep sight that doesn’t adjust low enough for the front sight.

      So I’m going to bend the barrel to compensate.

      B.B.


      • BB,
        I was really joking — it would affect any sight set with one component not in line with the bore. The normal sights (with the rear sight mounted to the barrel) should still work, even in this extreme case, though, right? I gave this enough thought to confuse myself lately when I discovered what I think was runout on the Ruger barrel. Also, shouldn’t one be sure the barrel is actually bent or drooping rather than runout before attempting to bend? Obviously, you KNOW the barrel is bent in this case. My thought is that bent barrel is correctable (over all ranges) by open sights (as long as both are on barrel and concentric to bore at that location) but that runout is not (for more than one range), since bore and sights are not parallel.


  8. Edith,

    Shouldn’t the title of this article be “Bending airgun barrels Part 2″ since Part 1 was published on July 30th?

    B.B.,

    Happy Birthday! So glad you’re still with us. Had my doubts a couple years ago. I have more grey hair now and blame you. Hope you have a great day and many more.

    kevin


  9. After shooting several 5 shot groups with Kodiak and Baracuda Match pellets, I discovered that my results were consistently better using the Baracudas at 20 yards. The Baracudas were 4.52 (sticker on bottom) and the according to the PA catalog, the Kodiaks should be 4.50 . The Kodiaks seem to fit the same and velocities were similar. What I also found interesting is that the actual pellet weight for either pellet is more like 10.2 gr and not 10.6 . Matching these pellets by weight did not seem to impact the groupings. Maybe, at 20 yards it doesn’t matter. However, pellet diameter had a much bigger effect on accuracy.

    Side note: I really like the new H&N screw top caps.


  10. Finally a test I could of aced, I would of been more than happy to bend a barrel for you!
    I bet you had a bit of a devilish smile when you pulled that trigger – did you have a pellet in it or did you really let it take one for the team?
    I probably would of been a bit nervous and flinched like I was shooting a .454.
    Still would of been a gas, speaking of which I just pd $4.00 a gallon. Always someones hand in my pockets.

    I do like the idea of keeping it bent as a dedicated long distance shooter. : )


    • Volvo,
      When I rode my motorcycle through Canada last June-July on the way to Alaska I paid over $5 per gallon through Alberta, British Columbia and Yukon. And on one occasion $6. Once into Alaska I averaged $4.80 per gallon. When I got back to the States gas was $3.65 and I thought I was getting a bargain. Sad, isn’t it? Never thought $3.65 would be a bargain.
      -Chuck


      • 3.65 IS a bargain! Gas is 5.40 a gallon here right now (1.43 per liter).
        A few years ago (+/-10) we had a price war going on for several months with gas as low as 1.89 per gallon (.50 per liter) and merchants complained so they set a minimum price at wich gas could be sold and they would still be making a profit (as if it was really needed) so gas prices went up and never went back down. Now CONSUMERS are asking for a pricing maximum but no one is moving a finger and gas companies are sticking it to us. The barrel price goes up, price at the pump goes up the same day, barrel price goes down and somewhere during the week prices will start going down again and you better not forget to full up your tank a few days before a long week-end because you can be sure the prices will go up. Makes me want a pedal car…

        J-F


  11. B.B., so it worth destroying the gun instead of rebarreling and selling it? That’s what I would expect for firearms. I’m amazed that you cannot see the bend while looking through the barrel when it is so obvious from the outside. When I look through bores, they look absolutely, perfectly straight, and I imagine that I could see deviation. As an aside, I understand that the marvelous, accurate barrels on Savage rifles undergo a final hand straightening process by experienced gunsmiths looking down the bores and making adjustments. So, the naked eye is not be dismissed for its precision.

    Duskwight, sounds like you’ve got it covered with the mushrooms. Eating mushrooms with gills would give me the creeps anyway.

    Matt61


  12. Since this air rifle is going to the dumpster anyways can any other destructive tests be done to it?
    Dry firing? Too much oil? Corn oil?

    J-F


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