Reducing Powder Chamber

[Pogue]

As mentioned in earlier posts, I recently acquired one of the Dixie 2 1/4" Coehorn mortars, and want to launch some billiard balls on the 4th of July!  However, I'm really concerned that the powder chamber is WAY too big (Dixie says to use 400-600gr).  I was thinking something more on the order of 50-100gr, so the ball will only go 100yds or so.

I have a couple of ideas for constructing an insert to achieve this, and wanted to get some "expert" opinions here.  I hope the attachment feature works, as this is my first try on this forum!  

Plan A is to machine an insert from brass, aluminum or stainless steel that is just under the bore diameter.  The powder chamber would not go all the way through the insert, but be more like a "cup".  The vent hole would be drilled and tapped so the vent liner would effectively lock the insert in place.  I figured an o-ring might be required in order to keep gasses from back flowing and blowing out the insert itself upon firing.

Plan B is essentially a permanent modification, where I'd just pore some molten lead and then bore out a 1/2" powder chamber.

Any ideas on this, or am I totally off my rocker?  BTW, any guesstimates on how far a pool ball would go with 400gr of BP?!

[Double D]

Is the bore of your coehorn all one diameter or is there a separate powder chamber?

If you have a separate chamber just reduce your charge to the amount you want load and fire.  As long as the billiard balls have windage and are  not a tight fit  you should not have problems.  Straight bore fire away.
The only concern I have is that the billiard balls may shatter in the bore and spew fragments all over.  Not good.

If the tube is straight bored and the fuse hole is to far forward for the fuse to reach a reduced charge placed in the bottom, then an insert might work.  Make it of steel and pin it in place. You will then need a vent liner going from outer tube into the powder chamber so that you won't get fouling and corrosion between insert and tube.

[Pogue]

Currently straight bored as shown in the diagrams.  What method of pinning do you speak of?  The only way I see would be with the vent liner as described.  TIA

[Pogue]

Actually, I just remeasured the vent from the base, and it's not as bad as I first thought.  About 1/2" with the 2 1/4" bore would be about 400gr if filled completely with powder to the vent hole.  But since I'm talking round ball projectile, there's plenty of room for the fuse to dangle to a shallower charge.

Or I could just foil wrap the charge so there's a thick wad of foil at the bottom, thin at the top!

[Double D]

Let me ask the first question I shouldhave aske now...Does this gun have a steel liner in it?

If it is just a cast Iron tube with no liner  Do not shoot it.

[Pogue]

Yes, of course it has a steel liner!

[Calamity Jane]

Casting lead inside steel will not work. Lead has a much larger coefficient of expansion and will loosen as it cools.

You could machine a "filler" from lead and drive it into place.

An O-ring will not take the heat or the pressure of BP

[Double D]

After a little more thinking I don't think a filler is a good idea. You have to have some means to seal the gap between filler and bore walls so gases don't seep between filler and out around vent, starting  hidden corrosion.

You idea about built up base wad in the cartridge seems the best.

One thing i would make sure of is that you have a vent liner to keep gases from getting between liner and casting.

[Fred]

The Hern coehorn (they make Dixie's) is a cast iron with a steel insert with a flat powder chamber the size  of the bore or rather no powder chamberat all. The 2.25 bore is a hard size to find projectiles for. I think a thin wall 2" elect. conduit will fit. My mortar was somewhat rusty when I got it so I used a cly. hone on it, to get rid of the rust and to oversize it some so I could find something to shoot.

I drilled and tapped the motar where Hern moulded in the vent hole location for a 3/8" or so (I don't exactly remember the size) bolt. I drilled a 3/32"hole through the center of the bolt and cut the bolt a little short of stickling into the bore but making sure it was screwed into the steel liner. Screwed it in with some locktite.

If you are concerned about a light powder load, insert your fuse first then add powder, or add powder, then fuse. That way the fuse will always be in the powder even if the projectile is past the vent hole, it will just push or bend the fuse, so when lit the fuse will burn past the projectile  ignite the powder.

Have not shot mine yet, need to make a base, and handling the proper size wood in a wheel chair is a little changeling right now.

You can get along quite fine without a powder chamber. I have a full size Mountain Howitzer with a 3.82 bore w/o a powder chamber and it shoots just fine.

"Do it to them before they do it to you"

FRED..........................

[Pogue]

Mine sounds like it was in the same condition as yours, rusty bore and all.  I take it you are not wrapping your charge in foil, just using loose powder?  I had thought of doing that, but all the safety rules I've seen said otherwise.

BTW, the 8oz cans used for energy drinks are 2 1/8", so they might be the way to go.  I've also heard of using sand filled racquet balls, which I happen to know fit perfectly (I won't say HOW I found out!).

[Fred]

For cannon I wrap my powder charges.

When loading small motars with a film canister or two of powder wrapped in foil, I would think it would be hard to place and pierce the foil wrapped charge, esp. if using fuze for ign.

What I have seen done, is to use a funnel (metal) and tubing, and pour the the powder charge in the mortar that way. Of course you do not look down the tube when doing this and you do not pour out of a full can of powder, dropping only the measured charge.  This way you can place the tube in the powder chamber, or spread it around the bottom of the tube if it has no powder chamber. If ign is by fuze using this method you can install the fuze before the projectile for sure ign.

FRED................

[maddmaxx]

As to lead as a chamber, it is likely to extrude some. To get an idea, take a block of lead and shoot it with a .22; makes a "splash".