TC barrel windage out by 20 MOA

[MistyMuzzy]

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.

 

[BoomStick]

I've got an early 70's renegade that shoots like that. I tried everything with the front and rear sights and could barely get it on a 10"-target at 50 yards. I figured there's bore run-out (sounds like you're thinking the same) and no sights mounted true to the barrel flats will ever align with the bore. Switched to a tang-mounted peep (the Lyman 57SML) which resolved the issue. The peep is also a plus with older eyes.

 

[MistyMuzzy]

I've got an early 70's renegade that shoots like that. I tried everything with the front and rear sights and could barely get it on a 10"-target at 50 yards. I figured there's bore run-out (sounds like you're thinking the same) and no sights mounted true to the barrel flats will ever align with the bore. Switched to a tang-mounted peep (the Lyman 57SML) which resolved the issue. The peep is also a plus with older eyes.

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.

 

[ETipp]

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.

You sure it’s not how the barrel is bedded in the stock?

 

[BoomStick]

With a patent breech, there's always a shoulder where breech meets bore. So being a little off center wouldn't matter. Most barrels are not machined after boring (just drilled from stock), and no guarantee bore and flats are parallel. Runout is known in early TC guns...but things can happen and maybe the cutter wandered mid-bore on yours.

 

[MistyMuzzy]

You sure it’s not how the barrel is bedded in the stock?

Thanks, I hadn't thought about this. I assumed the wood would comply to the barrel. I can see that the barrel doesn't sit centered in the barrel channel. I'll drift the underlug and see if that makes a difference.

 

[ETipp]

Thanks, I hadn't thought about this. I assumed the wood would comply to the barrel. I can see that the barrel doesn't sit centered in the barrel channel. I'll drift the underlug and see if that makes a difference.

I have been thinking about this. Perhaps one way to test this would be to get ahold of a laser of some sort, such as used to bore sight, that would fit into the muzzle. Clamp the rifle and stock into a vise and mark location on wall. Then remove the barrel and clamp it into the vise and do that test again.

Maybe I'm off base on this but it seems as if it might work anyway.

It just seems to me that if the barrel is not straight in the stock, as in the breech is off to one side more than the muzzle, that might be the snake in the woodpile.

 

[sussexmuzllodr]

Lets say a bore sight was inserted into a clamped, level and secured barrel. And the bore sight had no relative sideways slop in the bore. Could it be incrementally sent down the bore with an aim point on a wall or a sheet of wood? And as the bore light went further back into a questionable bore would a major change occur if the bore was off? Food for thought? Maybe?

 

[oldwood]

Take a close look at the muzzle crown. Is the bore worn at the muzzle?

 

[coupe]

mistymuzzy, I had a friend who owned a 50 cal traditions mountain rifle did the same but 10” left of point of aim. We tried everything but with the rear sight hanging out of the right side and the front out to the left made it 4” still left of poa.
We pulled the barrel fixed in a holder and a dial indicator mounted on it pressed till our spring back was less than our first static reading. A FEW THOUSANDS at a time. Did this twice now the poi is poa at 100 yards with the sights reset, all done gently, not like the guy who put the gun in a tree crotch and pulled it.
coupe

 

[MistyMuzzy]

mistymuzzy, I had a friend who owned a 50 cal traditions mountain rifle did the same but 10” left of point of aim. We tried everything but with the rear sight hanging out of the right side and the front out to the left made it 4” still left of poa.
We pulled the barrel fixed in a holder and a dial indicator mounted on it pressed till our spring back was less than our first static reading. A FEW THOUSANDS at a time. Did this twice now the poi is poa at 100 yards with the sights reset, all done gently, not like the guy who put the gun in a tree crotch and pulled it.
coupe

Coup,

Did you use a press to do this? Did you support the barrel at the far ends, or somewhere in between? I might try this myself, but I'm worried about hosing up the bore form.

 

[ETipp]

Take a close look at the muzzle crown. Is the bore worn at the muzzle?

That’s another good point. I sure as heck wouldn’t be trying to torque on that barrel until I have checked everything else first

 

[MistyMuzzy]

That’s another good point. I sure as heck wouldn’t be trying to torque on that barrel until I have checked everything else first

This is the extent of damage to the crown.

 

[Indy Durtdigger]

With that image blown up there are at least 3 places of damage to the crown right at the worst places. That's actual damage not wear from a ramrod, something has banged that up.

 

[MistyMuzzy]

With that image blown up there are at least 3 places of damage to the crown right at the worst places. That's actual damage not wear from a ramrod, something has banged that up.

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?

 

[Indy Durtdigger]

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?

I'd do a search on the forum and check out the different ways mentioned. By hand it's doable but easily messed too. Sure enough If I recommend a way someone will refute it as inferior.

 

[SDSmlf]

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?

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.

 

[MistyMuzzy]

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. ......

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.

 

[Indy Durtdigger]

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.

Quick question. You mentioned datum blocks and tanking the barrel to work to use a granite datum. Happen to work at a machine shop?

 

[MistyMuzzy]

Quick question. You mentioned datum blocks and tanking the barrel to work to use a granite datum. Happen to work at a machine shop?

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.