I’ve been trying to search to find a way to fix this myself as I’ve been a bit embarrassed to post the topic.
I have a 14.5" middy barrel from a reputable manufacturer. I have no reason to believe the barrel was delivered to me in anything but perfect condition.
In the course of trying to get an FH556-212 pinned/welded to make this of abritrary legal length the upper passed through a few hands that could share responsibility and naturally none are accepting it.
So, what I have in a now installed upper is a barrel that shoots a solid pattern 8" right of POA at 25 yards with max opposite windage dialed in on a KAC Micro 300M/ KAC Micro Front sight combo resting on a KAC URX 3.1/Noveske upper.
Visually, the curve in the barrel looks to start at/around the necking up of the barrel to the gas block and continues to the muzzle. Total deflection being right around 1/8" (estimate using the ole’ MK1 eye ball).
Is there any safe way to straighten out this portion of the barrel so that I can have enough adjustment to have a 100 yard zero or do I have $500 of wasted steel taking up space in my upper?
I didn’t try to zero my Aimpoint T1, but if there is enough adjustment in the red dot to zero at 100 yards would this still be a viable alternative to getting the barrel straightened?
Have you contacted so-called “reputable manufacturer” and told them that the barrel is possibly defective?
Is it possible that the KAC rail isn’t straight which is causing the sight issue? It’s rather difficult to simply bend a barrel unless someone beat it to death.
I would try and locate a barrel straightness gage and run it through.
Listen to IG - in lieu of a straightness gauge, I would try sticking a wooden dowel as close to .224 as you find down the bore and see if and where it binds up. Since your Mk1 eyeball can actually see the bend, it’s doubtful that an incorrectly installed URX is the problem. I would guess that it happened during installation/removal of your muzzle device - sounds like maybe someone got lazy and didn’t use a barrel vice. If worse comes to worse, many competent gunsmiths can straighten it for you, but it may be cheaper just to buy another barrel depending on how badly it’s bent.
The barrel is Centurion, I had not contacted the barrel manufacturer as I assume this was bent while in my or someone I had chosen to work on its possession.
In my trying to bend the barrel back, I can see how much force must have been required to bend it. Using a spirit level, the rail appears straight.
I tried the field expedient method of dropping a GI cleaning rod down it, it is able to make it through without binding. A straightness gauge is on my list of “to buy” tools now.
I did.
I installed the FH, the 25 ft lbs requires to torque it wouldn’t have bent it as I put waaay more force than that trying to bend it back.
You can see a severely bent barrel by sighting down the inside. An 1/8’ bend is severe, you will see it. Line up the concentric circles by sighting down in from the chamber end.
Yeah, I understand how difficult it can be to diagnose over text.
I’ve tried to take pictures, but I’m no Stickman and most my pictures make everything look nice and straight. Even when I use a straight edge and level to verify that the upper/rail is straight/level against my workbench for photos I can’t seem to get an angle to show the offset of the barrel other than a straight down the muzzle end shot.
I read online as a troubleshooting tip to shine a light down it and if the light came out as an oval or shaded it showed that the barrel is bent. Maybe I need a dimmer than 170 lumen flashlight, but I can’t find any light to be able to have this test ‘pass’ for a bent barrel.
Looking down through the rear end of the upper receiver, it does look as if the rifling isn’t straight, like the tube is curved.
Nope. The test barrel makers use (or at least, used to use back when it was done mostly by hand) was a big window with windowframes in it.
Look down the bore, out the window, into the sky. Move the barrel until you have the line of a pane frame in sight.
the line of the frame, running down the bore, will show if the bore/barrel is straight, or bent.
The old hands would sight a barrel, then use a barrel press to straighten it, and check again. In the better shops, if it took more then a couple of attempts to straighten it, the shop foreman would find out who the klutz was; the straightener or someone further up the line.
Look out your window, with something straight in view. use that, and get back to us. If you have any questions, use a barrel you know to be straight as a comparison.
Understand that there aren’t to many methods available that can straighten a of of steel, rod, tube, or barrel without knocking it out of roundness.
I’m not sure if there is a roundness, or concentric it’s specification to a barrel (I’m sure there as as designed by the OEM)…or additionally a straightness specification.
I just personally don’t know of any methods that won’t offset another dimension in trying to straighten.
If the ID of the barrel gets a flat spot or another form of indentation from OD input in trying to straighten…it may straighten the shit out if it. But make it dangerous to fire. I.e, the bullet hits a flat spot as it passes down the bore.
Then you and the barrel are both fucked up.
I’d contact the OEM to see about warranty on something like this before letting a “competent” smith “fix” it.
Just my .02…and I make Tubes, rods, shafts, and bars for a living…just not barrels.
A cleaning rod won’t work. You need something that goes into the barrel and fits inside almost perfectly. A real .MIL gage does this and will stop even if the barrel is dirty.
Another answer to the OP is that zeroing an aimpoint at 100 isn’t a viable alternative. Zero at a 100 won’t mean a thing at 200if the bullets zinging to the right as well as dropping. It will be that much further right at 200 and beyond.
Zeroing is only to account for ballistic drop (wind and other environmentals too) and essentially a perfectly straight barrel. So that from 100-200 you only have a vertical or minimal wind shift left right for such variables.
That damn good for your “ole’MK1 eye ball”. Using inverse tangent of 8"/900" (25 yards), an 8" worth of deflection at 25 yards, equates to angle of ~1/2 degree. Using similiar triangles, 8"/900" = x/14.5", with x - the barrel deflection coming out to ~0.129".
So just 3 thousandth off. Might have to re-cal your MK1 eye ball.
I’m unfamiliar with straightening presses, but if you were planning to DIY bend it back with weights, it’s probably more trouble than it’s worth. I did a quick calculation on bending stress. Assuming a constant 0.75" bore, 14.5" long, fully clamped on the opposite end of the force, solve for the force required to yield the barrel. Depending on the yield strength of the barrel in shear, 416 stainless can range from 20ksi to 80ksi based on heat treatment or lack thereof, which means the required force can range from 460 lbs to 1841 lbs. Keep in mind that’s a really simplified hand calc analysis, and even if you could do it, you’d have to be careful of the creep rate, period you load at yield as it deforms. Assuming you had the weights, and rig to do it, if you had a laser bore guide you could visual check it that way without deflection transducers.
If I had to guess I’d have to say its less likely a bent barrel and more likely either a slight rail misalignment, or possibly a slightly out of true receiver face causing deflection between the barrel and rail mounted sight. To fix you can either true the receiver face or very slightly realign the rail.
I had a bent barrel once. I wanted to order a custom barrel from a reputable manufacturer but they wouldn’t do the custom work themselves. They referred me to a reputable gunsmith who was one of their distributers. They suggested I order through the distributer and have them do the work. When I got the barrel the symptoms were just like yours, windage maxed out and crap groups. The bend was visible by removing the barrel and looking through the chamber and it also visibly wobbled when rolled on a flat surface. I contacted the manufacturer and at first they tried to say the gunsmithing voided the warranty but after forwarding the original e-mails where they told me to order through this distributer and have them do the work they relented and replaced the barrel. I was still out about $150 in custom work but at least it wasn’t a total loss.
i have a shotgun in my posession that was ran over by a tractor many years ago and bent the barrell. my dad got it for nothing and ended up taking the barrell off and plugging one end and filled the barrel full of fine sand and plugged the other end. then proceeded to stick it between two oak tree’s and pull on it very slowly until he couldn’t pull it anymore. the barrel would only go back to where it was straight and wouldn’t go anymore. i don’t know if this would be safe on a .223 barrel and i am talking about a more forgiving shotgun barrel but i can’t see where this thing was ever bent.
