Removable Vent Liner

[Farmer Dean]

Concerning installing a vent liner in my Model 1841 Full Size Six Pounder 3.5" bore(Hern). I know I have read that is important to have a vent liner in a barrel with a liner. I understand that is necessary with an older piece that has been lined at a later date. However, when a piece is created by pouring over a liner, doesn't that create an effective one piece barrel. In other words doesn't the molten iron fuse with the steel liner creating a seamless joint?

None the less, I was hoping to get some some ideas about installing a threaded liner. Firstly, I'm assuming I should tap course (NC) threads? Since I'll be using 1/8" fuse I will make a 3/16 vent hole. I haven't decided on whether to use Copper or Stainless as a vent tube. What's a good diameter bolt to start with? I feel nervous about drilling any larger diameter hole that necessary.

Since my liner is 1/2", if I understand this correctly I will first drill a 3/16" hole all the way through, and then drill my larger (to be threaded) hole - stopping 3/8" (?) short of punching through. I then have my bolt drilled and the end chamfered to match my drill chamfer. Lots of anti-seize and that's it, or do I need to help the seal where bolt and liner meet?

Do I want a slight angle on this vent or just head down at 90 degrees? My barrel manufacturer had no ideas or specs on any of this and recommended  that this board would know best.

[gary michie]

HI;
You would like to think that a 2000 deg. pore would become one with the liner and I'm pretty sure that most of the time it  dose, but last year there was a vid. where a person with a hammer was knocking off iron off a liner of a tube made overseas.
 My cannon is a parrott steel tube and I lined the vent with a 3/4 copper rod threaded with N.C. with a 1/4 bore a unthreaded section3/4 length beyond the barrel, then a 3.4 inch above it squared off to put a wrench on.  I install it with anti-seize lube to insure removal.
Gary

[Farmer Dean]

Gary, did you drill and tap your 3/4 hole all the way through the barrel (liner)? Where your unthreaded copper comes out the top to the squared off end, did you leave that end or did you hack it off flush after installation? Dean.

[Articifer Tom]

 Hello , I posted you a pm which your welcome to post here . One thing you ask I didn't answer  . Did my gun at 90 degrees and flushed to top of barrel. I also have photos of my assembly . Just don't know how I can post them.

[Rickk]

Not all Hern barrels are set up to be drilled at 90 degrees. Most originals were drilled at an angle as well. If there is a precast dimple to start drilling, and you go in at a 90 degree angle, you may not enter where you hope you would.

Measure twice, drill once. If you are not able to figure it out by measuring, lemme know. The guy who drilled my mortar came up with a technique that is much harder to describe than to actually accomplish that worked perfectly.

Rick

[Farmer Dean]

Rick, there's no dimples on the casting. I read somewhere that the reason they often went at an angle was to 'increase' the thickness at the vent hole. I also thought I read where if possible it's best to vent straight up so as not to blow fuse embers any farther behind you.

I was just going to do some careful measuring to come up with a drill location. Dean.

[Articifer Tom]

 Be sure it is not to far back seen one gun was only 1/8"off back. The foil was getting pricked between the layers, causing misfires.

[gary michie]

HI:
My vent is at 10 deg.and 3/4"N.C. all the way to the chamber but close to being slush. The top is about 1.25 to 1.5 proud of the outside of the tube.I use 209 primers so I need a hammer to fire them and it snaps on the 3/4 round part of the vent. I cut a ring there for it to snap into.

[Double D]

Gary, got any pictures?