Locating front post hole

[peter nap]

I have a couple of H&R Ultra Slug guns.
One has been rechambered for 3.5 (12ga) and I ran across a peep sight for it several years ago.

The peep fits the scope mount holes so that's done.

There is no taper to the barrel and the peep is very low, so I'm just going to install an Ivory post for a front sight.

There is a way to locate the hole without buying a Jig using a piece of angle iron. I've never done it and can't find where I read about it.

Has anyone done this or have a better way?

[DCM]

Do you have access to a large mill that is true?

[KCSO]

You can buy a center locater for your drill press fairly cheap, it will not be as true and a good job on a mill but should be close enough for a shotgun sight. The tool looks like a Y that swivles and fits in the chuck. Put it on over the barrel and crank it till it centers this is close to the center of the barrel. BUT you have to have the barrel square in the drill press.