Breechplug to primer hole

[Ezra]

If I remember correctly, optimum distance from front of the breechplug to the center of the priming hole is 1/4"?  Or so?  It is a .58 caliber rifle, if it matters.


Ez

[D. Taylor Sapergia]

I think that the "ideal" position for the vent is right at the face of the plug, or in other words, as close as you can get it.  When using a liner, however, with a barrel wall that is thinner than the length of the thread section of the vent liner, it is necessary to place the liner far enough forward of the breech plug face so it does not interfere with the plug.  So, with a 1/4" journal on the liner, the vent will be ideally placed 1/8" + a few 'thou' forward of the face.  And so forth.

[Acer Saccharum]

The closer the touchhole to the breechface, the better, in my opinion. If you use a liner, then there are other considerations.

For a flat faced breechplug:

Plain hole: drill minimum 1/2 the diameter forward of the breech.

Coned from the inside: drill half the diameter of the largest diameter of cone forward of the breech.

Liner: drill for liner 1/2 diameter of the liner thread diameter forward of the breechface.

[docone]

If the primer hole is 1/2 the face of the breechplug, then is it feasable to tap the drum and then install the breechplug?
I prefer percussion, and my thoughts would be to have them lock together that way.
I like patent breechs, but I have not tried a drum type yet.