Threaded vent.

[passgas]

I bought a used full scale 1841 Mountain Howitzer. It is a steel lined bronze barrel with a 3" bore. The outside diameter around by the vent is 6.2" The vent was a direct vent. The vent hole is getting out of spec in the .25" range. I need to have a threaded vent made and the tube drilled/threaded for the new vent. So I have a bunch of questions. Friction primers are the source of ignition.

 

What size vent plug should I use? Does 1" sound correct?

What thread is used? Straight or tapered?

Fine thread? Class of thread?

Material of thread? Copper?

Would the machine shop rebore the area where vent protrudes down in barrel to make it flush or just screw it down to flush?

Should be no problem to couture top portion of threaded vent plug?

 

The more info I have to give the machine shop the better off I am.