Charging a mortar?

[Evil Dog]

I recently acquired my first mortar, a 1.75" bore Coehorn replica.  It has a 1" dia x 1.5" deep subchamber for the powder charge.  Being brand new at this I am at somewhat of a loss as to how to properly charge this with powder.

I do have quite a lot of experience with muzzleloading rifles and pistols, been shooting them since the late-60s.  One of the cardinal rules is never leaving an air space between the powder charge and the ball as then the ball would be considered a bore obstruction rather than a projectile.  I presume the same concept would also apply to a mortar.

Filling that subchamber with FFg though would seem to be rather excessive for launching golf balls.  So far I've tried pouring a loose powder charge into the subchamber and then filling the remainder of it with greased cardboard wads.  That seemed to work but was a total pain putting a half dozen or more cardboard wads in one at a time.

Making up aluminum foil wrapped charges seems to work a lot better.  The breech end of the cartridge contains the powder with the balance of the cartridge filled with yellow cornmeal.  The cartridge is marked with the powder charge and an arrow indicating which end to insert into the subchamber.  They are made just under 1" dia to slide into the subchamber and then seated with an appropriate ramrod flush with the mouth of the subchamber.  After the ball is placed in the bore I use a pointed brass rod to puncture the foil cartridge through the vent hole and then insert a fuse.  This seems to work much easier than the loose powder loading... after the shot has been fired I use a long set of tweezers to remove any remaining aluminum foil from the subchamber and bore.

Although either method seems safe enough, I would like to know from you experienced mortar shooters just what is the proper procedure for loading the smaller mortars?

I value your input.

[Double D]

There are differences in the way shoulder fired fire arms and cannons & mortars are loaded and fired. There is also a difference in the way a Cannon and mortar are loaded

In a black powder shoulder fired firearm the projectile is a fairly snug fit down the bore.  If you tip the muzzle down the projectile should not slide out. The projectile is seated against the powder charge. Leaving an air space is considered dangerous in shoulder fired firearms.

Cannon and Mortar projectiles are different.  The projectiles in cannons and mortars should have what is called windage.  The projectile should freely slide or roll the full length of the bore.  The projectile should be .010” to .015” smaller in diameter than the bore. If the muzzle is pointed down the projectile should slide out of the bore.

When loaded the cannon projectile goes down the bore to be seated against the charge. “No air space” Because of windage it’s not possible to set it tight.

The mortar is different.  In a properly made mortar you have what is called the chamber and the larger projectile diameter bore.  This is misleading.  The chamber is really the bore.  The area where the projectiles rides is more properly called an expansion chamber and projector tube. The projectile is really sitting on top of the muzzle. It’s not possible to get the projectile seated against the charge.

  When fired the hot gases come out of the powder chamber or bore of the mortar, hit the bottom of the ball and start expanding outward around the ball into the large expansion chamber. The gases meet no resistance to the expansion and are given time to move the ball.  Plus they can flow around the projectile further reducing pressure.

Just the same I would not fire my Mortar with unnecessary air space.   I do not load loose powder in my guns.  I make a cartridge.  For reduce charges just add wad to make the cartridge long enough to fill the chamber.  If you go to the post here on the board called Loading Cannon Cartridges you see instruction furnished by Peter Jorgensen Editor of the Artilleryman in the proper procedure for making cartridges.