3/4-10 Breech Plug: Update

[Khym]

I drilled and tapped the breech of the Numrich barrel.  I followed that with a bottoming tap I made.  As seen in the photo I coated the shoulder of the hole with Prussian blue.  I tightened the breech plug as far as I could but after removing it I found no smears of the Prussian blue on the face of the plug

The depth of the hole is .613.  I was able to tighten the plug to a depth of .598.  As I understand it the plug must be flush with the shoulder of the hole.  That being so I’m still .015 shy of having the face of the plug flush with the shoulder of the hole.

If that’s still too much of a gap I’m considering beveling the face of the plug to the diameter of the bore so that it just barely protrudes past the shoulder of the hole.

Suggestions are welcome!

[flinchrocket]

You want the face of the plug to seal up against the shoulder to prevent black powder grud from getting in the treads.

[bob in the woods]

It's not a matter of "too big of a gap".    There shouldn't be any gap whatsoever as per flinch rocket's post

[Khym]

That it isn't firmly resting against the shoulder is why I'm wondering if I should bevel the face of the plug.  What is it that I haven't done that is preventing this from happening?

[flinchrocket]

Most likely, since you can't get treads all the way to the shoulder you will have to remove the first tread or so on the plug. Some type of transfer color ( candle smoke, magic marker ) will tell you where it is bottoming out. You don't want to bevel the plug. A square plug against a square shoulder, tight all the way around

[Clint]

Color the whole end of the plug with a magic marker, then screw it into the barrel. Make sure that you put some torque on the bolt and back it out. You should see where the threads are interfering and you can adjust it with a triangle file. If you have some aluminum floating around, mill a set of vise jaw inserts to fit your barrel so you can get the torque up without twisting the barrel out of the vise.

[Bob Roller]

If you drilled it the the angle of the drill's point must be taken into the mix.
That bolt will never work until it has a FLAT edge to crush against.You might
reangle the bolt to match the angle of the drill's point.
Bob Roller