The math of bending barrels

[remuse]

I do intend to find a nice forked tree to do a little barrel adjustment. What's the math to determine amount necessary to raise poi 6" at 20 yds?

(I'm going to work on my flinch to correct the other 18"!)

 

[airmansteve]

well sir, I would tweak those sights to kingdom come before I ever bent a barrel. to raise the POI, raise the rear sight (if its adjustable) or lower the front sight.

and a stupid question, you are lining up the top of the front sight with the top of the rear sight, aren't you?

good luck, keep making smoke!

 

[David W.]

I agree with tweaking the sights.

 

[remuse]

My apologies for forgetting the tendancy of folks on this board to keep people from doing stupid things! I should have said initially that I have no rear sight and my front is a nubbin (.62 trade gun)so I've got no where to go adjustment wise unless I add a rear sight.

 

[Semisane]

If you decide to try a bend Weston, you need a lenght of 4'x4', some small blocks of wood, and a large C-Clamp.

 

[ohio ramrod]

The only suggestion I would add to that set up is to contor the blocks to the barrel so you don't push in flat spots. A little bondo and aluminum foil will make some contor blocks. Also a dial indicator will help you measure how much bend you put in. Remember you will want to "over bend " to allow for "snap back" when the pressure is removed. I worked for years at a company that regularly straightened gears with a fancy machine that was nothing more than a heavy duty set up like yours.

 

[tg]

Most of the top builders will recommend bending the barrel and it has worked for a long time, it is nothing to be afraid of and there are several "Jigs" that can probably be found in the archives if a tree crotch does not suit ones fancy.The one shown above is probably as good as any.

 

[larry wv]

I have bent a lot of shotgun barrels on trees and truck bumpers. (thick barrels). It doesn't take much of a pull or tug to do it. If you go that route tug a little and shoot till its where you want. I traded into an 870 barrel that shoots off a bit it will get tweaked before long. Larry Wv

 

[Zonie]

I'm afraid I agree with the others Weston.

Bending a barrel is different than adjusting the height of the sights.

There is no guide to determine where your barrel will bend and often it is not a uniform bend from breech to muzzle. This is especially true with tapered or octagon to round barrels.

Because there is no good way of knowing where the bend will happen, there is no way of setting up a mathametical formula to calculate how much you will need to bend the barrel to adjust its point of impact 6 or 16 inches at 20 yards.

Good Luck.

 

[J.D.]

IMHO, and by experience, you don't need C clamps or calipers, just a few 2X4 blocks and a floor. For that much elevation begin by using about three 2X4 blocks stacked on the floor. Put your weight on the top center of the barrel. Put it back in the stock and shoot it. Remove from the stock and adjust as needed.

God bless

 

[odean]

The mathamatical formula is based on the distance between the sights in inches and the distance to the target in feet, so if you only bend between those two points you may be able to work out something.(To find the sight correction in thousands of an inch, divide the distance the bullet strike needs to be moved by 12; then divide that figure by the distance to the target in feet; then multiply that figure by the distance between the sights) If you have no rear sight I would guess you could consider that your "eye" is actually the rear sight. Oscar/NC

 

[remuse]

Now we're talking! To move 6" over 20 yds with a 36" barrel, I figure .30 inches. That certainly seems like a manageable project with a certain pc flair.

 

[CoyoteJoe]

I think you should re-read Zonie's post. Your calculation would be correct for adjusting a peep sight but bending a barrel in the middle is entirely different and .3" inch would be one heck of a bend, I'd start with no more than .1", shoot and try, there is no shortcut.

 

[upperplains]

I straightened a barrel once but found that you actually have to overbend a bit because the barrel had a tendency to spring back. It took several tries before I pressured the barrel enough to move it. I then just checked the straightness on the outside of the barrel with a steel straight edge until it looked good and did the rest with the sights for point of aim.

 

[remuse]

No, I understand that. Along with how to do it, I was just trying to establish what sort of incremental movements I need to be thinking about. And obviously they are very small!

 

I could tell you about a dozen stories about guns that were brought in to the shop after the owners tried to do their own barrel bending. The most common involved dents or inward bulges with a few cases of "I bent it too much and tried to go the other way" thrown in. In the latter cases the barrel often had a visible "S" curve. I'm not saying that it can't be done successfully because it obviously has been by people. If you want to try it take it slow and easy. An even better suggestion is to spend a few minutes with some files and install a rear sight. It's a better solution all around.

And, since you mentioned flinching, have you sat down at a bench and fired the gun off sandbags? If nothing else, this will give you a baseline for where the gun is really shooting with much of the human factor removed. Just a thought.

John