Hern's Coehorn Mortar Vent Hole

[powder2burn]

I was given a Hern's coehorn mortar. I told my story on how the vent hole got drilled.

Rickk wanted to know how far from the bottom by vent hole was. Yesterday I measured it the best I could. It about 5/8 In or a little less from the bottom of the bore.

The vent hole was finally drilled and then tapped. ( I forgot the size ) I used a grade 5 bolt and drilled a vent hole through it to take cherry bomb size fuse. I "trimmed" (bet that's not a machinist's term) the bolt so I could no longer see it in the bore. I used anti size on the bolt's threads and screwed it in. I left the bolt head on to make it possible to remove. The cherry bomb size vent hole is to small as it gets clogged up after a few shots.

[Double D]

Fuse hole should be  1 1/2 calibers in diameter.  That is 1 1/2 time as large as the fuse.  1/8 fuse, 3/16 fuse hole.  You need a vent punch to clear the hole after firing.

[powder2burn]

 I get two maybe three shots, Just haven't been shooting that much and haven't bothered to redrill out the fuse hole.

[Rickk]

If you use paper straw quills (3/16 od) you will need a .200 hole. Depending on the situation, quills are safer than fuses. .200 is fine for 1/8 inch cannon fuse as well. A .22 caliber brush fits it for cleaning purposes.

Anti-seize is good idea, I use it on just about everything I take apart that I might want to take apart again. Maybe consider a stainless steel bolt as well?

How about a picture of this?... this sounds good. Vent liners get talked about alot, but not seen often. What size bolt did you use?

Vent punch... I use a 3/16 brass rod with a loop formed on one end. The other end has a square bottom. I use it both to clear the vent and also to puncture the foil bag.

I was using a pointy version of the same tool for puncturing the bag, and had occational misfires. I tried the square bottom vent pick to puncture the bag and misfires went away. I am thinking that the pointy one poked a hole, but left the foil in the way. The square bottom one probably actually punches the foil and pushes most of it inside the bag - out of the way.

[Double D]

Here is my only vented tube...My golf ball mortar.

[Rickk]

DD... trying to read the markings on the head... doesn't look like grade 5... stainless?

What size hole, what size bolt, and what does the other end of the bolt look like?

One thing that bothers me is that the N-SSA makes all sorts of fuss about the shape of the breech plug face, but then there is this threaded hole with a bolt stuck thru the side. It would seem that unless the bolt end is cut and contoured very carefully to try to match the bore ID wall surface that the threaded hole would be a good collector of smoldering stuff.

[Div Arty]

   
     If I install a vent tube in the form of a 5/l6th in. bolt with a 3/l6" vent hole and later want to upgrade to a musket nipple for 0300 CCI caps.  I must drill the nipple out to 3/l6" to accommodate the vent pick.  Question, that doesn't leave much wall for the cap anvil.  As you can see in the enclosed picture, the OD of the nipple is only 1/4".  This is for a 1/2 scale 6pounder.

                Thank you, Div Arty

[Double D]

That is a standard Home  Depot bolt of large enough diameter to be drilled out  1 1/2 calibers for the fuse  and long enough to reach but not go in the powder chamber.

This is what a vent liner looks like.



Heres how it fits.



The beveled end seats against the beveled bottom of the .  There would be no step at the bottom, I put that in there for illustration purposes. The nose of the vent liner would not protrude significantly into the chamber to matter.

We only need a vent liner if we are using a lined tube.  A tube made of solid piece modern steel doesn't need a vent liner..  doesn't hurt anything if you have one, but not needed.