TC barrel windage out by 20 MOA

[Indy Durtdigger]

I'm a mechanical engineer, so I'm familiar with machining processes and have access to granite blocks and measurement instrumentation at work. Our workplace is filled with shooters and hunters, so I get no gas for bringing in gun parts over lunch break.

Ah cool. My daughter is an ME and son a machinist of sorts. He runs CNC but I'm hounding him to ditch the computer and learn how to actually do it himself. Dying skill set like mine.

 

[SDSmlf]

SDS, thanks for so much detail, and a more scientific at-home approach.

Do you find the 60deg chamfer to be optimal? It currently appears to be 45deg.

I have both 45° and 60° chamfers, plus some radius finished muzzle bores. Hard to say what performs best…. For now I’ll say I prefer the 60°, though they all work.

 

[Uncle Miltie]

Someone might have de-breeched the rifle and reinstalled the plug so the barrel is slightly canted to one side. This would also cause a less than perfect fit of the barrel in the channel of the stock.
An improper fit of the breech plug with the tang could also cause the problem you describe.

 

[MistyMuzzy]

Someone might have de-breeched the rifle and reinstalled the plug so the barrel is slightly canted to one side. This would also cause a less than perfect fit of the barrel in the channel of the stock.
An improper fit of the breech plug with the tang could also cause the problem you describe.

That is also something I hadn't thought of. The breech plug to barrel fit is really nice and I don't have the impression that the finish had been redone, but I will consider this going forward.

(The yellow tubing over the nipple is a piece of tygon fuel line for dry fire practice.)

 

[ETipp]

Are you going to be shooting round ball or conical?

 

[Bad Karma]

You can work it with your thumb and see how it cleans up as some folks like to use their thumb over fine grit wet sandpaper to polish a crown, and it seems to work.

Personally, I like to cut a 60° chamfer with a lathe, then polish. Belts and suspenders approach proven to work. Without or without a lathe, I would have used the ball bearing process I have posted about here a number of times.

Using a series of ball bearings (guess you could use glass balls or marbles), from about one and half times the bore diameter, to right around bore diameter, and using sandpaper of different grits from 120/180 up to 320 or finer (I take it up to 1000 grit
if I want a mirror finish, think working on someone else's gun). A couple of turns of the muzzle over each ball bearing with progressively finer sandpaper over them gives a smooth barrel crown to bore transition.

Basic idea is to hold the sandpaper over the ball bearing (you can place ball on the floor and hold paper with your feet, maybe on a pad or thin carpet if you don’t have a lathe to chuck up the barrel in) and rotate the barrel bore on the bearing with the sandpaper on it. Easy to keep barrel square with the floor. I’ll start with the larger diameter bearing and roughest grit paper and end with a smaller ball bearing near bore diameter, repeating with progressively finer grit sandpaper. I stop when I have a slight chamfer on bore and rifling lands that is highly polished.

I use Dykem (or a Sharpie) to mark the inside the bore so I can easily see when I starting to clean up everything without going too far. Note the 60° chamfer in the photograph was cut on a lathe, I just use the ball bearings to break up the lumps and sharp edges and polish the crown.

Note that with any method involving sandpaper, and your barrel is already finished, you are going to remove finish from the face of the bore if you don’t protect it. I’ve used ‘masking’ tape with a hole punched through it (use a wad punch), but only on other people’s gun’s, not worrying about the finish on mine.

This is the way…

 

[MistyMuzzy]

Are you going to be shooting round ball or conical?

Round ball for now. I might try conicals if I ever draw my preferred elk permit.

 

[M. De Land]

I've got an pre-warning TC .50 cal octagon barrel that is about 20 MOA out on windage. The barrel does not seem to be bent when I lay it on a flat datum. The barrel groups well, but I have to offset the sights by .065" in either direction to match point of impact to point of aim. It's probably not a big deal but it looks goofy to me and I do worry about the sights being at extreme points in their dovetails. Otherwise it's a beautiful barrel that doesn't look to have been shot hardly at all.

Is this something that a gun builder can fix by either bending or boring? I imagine that the boring tool would just follow the existing bore and end up with the same issue.

I'll try some other loadings, but the 60gr FFg, .490RB with pillow ticking that I have been shooting seems like the gold standard.

You'll need to look down bore at a clear window and rotate it to see where the crook is. Sounds like the deep hole bit wondered a bit and the bore is not straight although the flats may be orientated on center with the end holes.It helps to look at a vertical wire or string plumb bob viewed through the bore at the window.. As you rotate the barrel the shadow line will show where the bore deviates off line.
Some times the bore is tangential to flats and not have a curve to it but the fix is the same with orientation in the vertical plane.
I have to check this all the time when I thread and fit a barrel to an action so the crook is orientated in the vertical which is much easier to correct for and not require any barrel sight set over much off center line..

 

[coupe]

Misty Muzzy, I agree with De Land but contend where ever the bore is off on the interior the ball only goes where the bore end is pointed. Yes I blocked the ends of the barrel and used my shop press to gently bend the barrel, and not by much at that using a dial indicator to monitor the bending and check the set on the barrel. It took ok cause he reset the sights almost barrel centre and shoots a 3” group at 100 yards.
coupe

 

[Rebel bull]

The bore at the muzzle is centered, and if the bore at the breech was out by .100"+, I imagine that they would have trouble getting full cleanup on the breech plug. Also my understanding is that they drill the bore, then put the barrel on centers and then mill the flats for the octagon, which means that the breech and muzzle bore should be really close.

This means that there is either runout mid bore, or I have a banana barrel that I can't pick up with my countertop datum. I'll bring it into work tomorrow and put it up on the granite plate.

another thing you can do is to relieve the crown just remember that you relieve the side opposite the direction you want the ball to move just like moving the front site

 

[Siringo]

This is the extent of damage to the crown.

Are you shooting roundballs? If so correcting that muzzle damage may not help. Round balls aren’t effected like slugs. However a maxi ball would be effected. But 10 inches is huge. I had a green mountain barrel that did this and it had quite a bit of runout.

 

[stikshooter]

Are you shooting roundballs? If so correcting that muzzle damage may not help. Round balls aren’t effected like slugs. However a maxi ball would be effected. But 10 inches is huge. I had a green mountain barrel that did this and it had quite a bit of runout.

Or a cheap quik fix is text Toma Hawk and get one of his tang mounted peep sights ($100+) better sight than factory , love mine and probably fix your issue as long as it groups now /Ed

 

[ETipp]

Or a cheap quik fix is text Toma Hawk and get one of his tang mounted peep sights ($100+) better sight than factory , love mine and probably fix your issue as long as it groups now /Ed

Yep, it might work but there really isn't any windage adjustment. As bad as his rifle is out, I have my doubts.

 

[OldNo7]

Some research on MLF says the easy way to clean those burs up is my thumb and some 220 grit. Is that still the recommendation?

This tool is offered on ebay for little money... I've used similar ones on several BP and CF rifles and always saw an improvement.

Old No7

Brass Muzzle Lap 5/8" - Gunsmith Tools

 

[ETipp]

Round ball for now. I might try conicals if I ever draw my preferred elk permit.

I was going to recommend a Joe Woods coning tool but its not recommended for conical.

 

[Acorn Mush]

You can work it with your thumb and see how it cleans up as some folks like to use their thumb over fine grit wet sandpaper to polish a crown, and it seems to work.

Personally, I like to cut a 60° chamfer with a lathe, then polish. Belts and suspenders approach proven to work. Without or without a lathe, I would have used the ball bearing process I have posted about here a number of times.

Using a series of ball bearings (guess you could use glass balls or marbles), from about one and half times the bore diameter, to right around bore diameter, and using sandpaper of different grits from 120/180 up to 320 or finer (I take it up to 1000 grit
if I want a mirror finish, think working on someone else's gun). A couple of turns of the muzzle over each ball bearing with progressively finer sandpaper over them gives a smooth barrel crown to bore transition.

Basic idea is to hold the sandpaper over the ball bearing (you can place ball on the floor and hold paper with your feet, maybe on a pad or thin carpet if you don’t have a lathe to chuck up the barrel in) and rotate the barrel bore on the bearing with the sandpaper on it. Easy to keep barrel square with the floor. I’ll start with the larger diameter bearing and roughest grit paper and end with a smaller ball bearing near bore diameter, repeating with progressively finer grit sandpaper. I stop when I have a slight chamfer on bore and rifling lands that is highly polished.

I use Dykem (or a Sharpie) to mark the inside the bore so I can easily see when I starting to clean up everything without going too far. Note the 60° chamfer in the photograph was cut on a lathe, I just use the ball bearings to break up the lumps and sharp edges and polish the crown.

Note that with any method involving sandpaper, and your barrel is already finished, you are going to remove finish from the face of the bore if you don’t protect it. I’ve used ‘masking’ tape with a hole punched through it (use a wad punch), but only on other people’s gun’s, not worrying about the finish on mine.

After checking for any bedding problems, my humble opinion is to try SDFmls’ suggestion as an easy preliminary step prior to attempting anything more drastic such as bending the barrel. I wish you success in your endeavor.

 

[dave951]

Before molesting the rifle, let somebody else shoot it to rule out operator error. True story- I had an adult Scout leader constantly off 6in right at 30yd. Great groups just waaaay off. Everybody else shot the same gun dead center. Found out the leader hitting 6in right had eye surgery as a child.

 

[45man]

I have had bent TC barreks and used two wood V blocks and a large C clamp to get them straight on my bench. protct the barrel with wood under the clamp. I also use ball bearings on the crowns but I silver solder a rod to them and use lapping compound.
the one shown by SDSmif is perfect, great job.

 

[MistyMuzzy]

*** Update ***

I put the barrel on a proper datum today and found that it is .020" out of straightness, in the expected direction, and biased towards the muzzle. Measuring either side was the same (opposite directions), so I think the straightness problem is real, and not just a defect in the octagon flat. I will however try all of these good suggestions before resorting to bending the barrel.

 

[Bad Karma]

*** Update ***

I put the barrel on a proper datum today and found that it is .020" out of straightness, in the expected direction, and biased towards the muzzle. Measuring either side was the same (opposite directions), so I think the straightness problem is real, and not just a defect in the octagon flat. I will however try all of these good suggestions before resorting to bending the barrel.

I believe I’d straighten the barrel, re cut the crown and go shooting. With the tools you have at your disposal it should be a piece of cake.