Locating top of round barrel for sight mounting

[Frod733]

Hello all,
I have a round rifle barrel that I will ultimately be mounting front and rear sights on. What is the best way to determine the top of the barrel for fitting dovetails? Thanks.

 

[doubleset]

I have no intention of trying t answer this myself, but I'm awaiting answers with great anticipation. Personally, I regard finding the exact center of a tubular surface to be one of the most challenging problems for the amateur machinist, and that's without even first deciding what "top" means in a particular case.

 

[Frod733]

Tried to find some dovetail jigs/fixtures/guides, but they don't seem to be available any more. I am attempting to cut them by hand, not by machine/lathe.

 

[2 shots]

maybe cross feed vise and a dial indicator ??

 

[2 shots]

the log cabin shop and several others have them in stock.. dovetail cutting guide.. midway has the instructions online.. hope that helps.. mike

 

[Frod733]

Thanks. The Log Cabin shop shows one (I think for octagon barrel though) but it says: "Availability: 9935" ??????

 

[doubleset]

But finding a jig doesn't address the original problem of finding the "top of the barrel". Two different problems, eh?

 

[jsb30]

You find a place on the receiver you can level off of like feed rails or recoil lug. I use a B Square sight drilling jig. Barrel is held in (V) blocks and receiver is held square with a support. For drilling and tapping it has drill bushings on a sliding arm. Milling dovetails it is leveled both ways in (V) block sideways in milling machine vise.

 

[Flintandsteel]

Lay that barrel upside down on a good flat surface. Lay a fine file under the muzzle area where you want the sight, hold the top flat firmly on the flat surface, and slide the barrel back and forth a few times.
You will then have a mark perfectly centered with the top flat.

 

[deerstalkert]

just as Flintandsteel says, only with a round barrel you will have to use the breach plug or tang to determine that the top of the barrel is on the file.
use a square on the side of the breach plug/tang and the bench top.

 

[OkieDougie]

Assuming you can identify the breech end's center Hang a plumb bob so it just touches touches the top of the barrel on the breech end. Plumb bob just touching the muzzle end will also be just as centered as the breech end.

 

[The Crisco Kid]

Assuming you can identify the breech end's center Hang a plumb bob so it just touches touches the top of the barrel on the breech end. Plumb bob just touching the muzzle end will also be just as centered as the breech end.

How do you move the plumb bob from the breech end to the muzzle and keep it centered? Or how to move the barrel under the plum bob and keep it centered? A milling machine with a lot of travel would work but not many people have access to that. Maybe that's why octagon barrels were thought up?

 

[doubleset]

I knew this was going to get good.

 

[oldwood]

I've done many round barrel sight locations like this. Best to have the barrel out of the stock. Attach a fine piece of cord to the top dead center of the breech plug tang. Fishing line is fine enough , and strong enough. With the barrel in a vise , leveled , the best it can be with the eye. Tape the cord at the muzzle end , positioned by eye. Mark the position of the cord with a 1MM marker pen. If all looks good mark the position of the cord with a thin scratch awl. ..................install the sight....If using solder, be frugal with the solder. Solder on steel can be easily cleaned up with a Dremel tool using a stainless steel wire brush .......oldwood

 

[yonderin]

Thinking that what is meant is to hang a plumb bob, hold the barrel so it is centered at the breech end and consequently will be centered at the muzzle.

 

[sheriff john]

These gonna be dovetails front and rear ?

 

[OkieDougie]

How do you move the plumb bob from the breech end to the muzzle and keep it centered? Or how to move the barrel under the plum bob and keep it centered? A milling machine with a lot of travel would work but not many people have access to that. Maybe that's why octagon barrels were thought up?

Two separate pumbs, used at the same time . Barrel on flat surface beneath the frame. C clamp or whatever else laying around to clamp the barrrel still.
Just a simple tool solution to find the same center on both ends of a pipe. How to cut and install a frnot sight accurately without a milling machine though, That I have no idea other than...close enough for govt work.

 

[Greasecookie]

Back in "the day" they used "the bones". Two pieces of flat stock, lay one on the flat of the tang and , with an assistant position the other at the end of the barrel and sighting down the barrel, when "the bones" are aligned horizontally, the assistant marks the intersection of the round barrel and "the bone". Or do what I do, use a Forster sight jig to mark the dead center on the top of the barrel vs. the flat of the tang. But those jigs are kinda spendy for one dovetail operation.

 

[The Crisco Kid]

Another way that might work is the use of two parallels. One on the breech plug flat and the other on the muzzle. If they line up by eye ball the one on the muzzle would be TDC. This is an old school way of getting a stock blank flat and on the same plane from one end to the other. As far as cutting the dovetail without a milling machine just cut down to 15 or 20 thousands less than the sight base thickness with a hacksaw and get it to final dimension with a 3 cornered file with one side ground safe. This is where the parallels would come in handy to keep things lined up.

 

[deerstalkert]