Temporary aluminum bore liner

[cannonmn]

I'm not sure if I'll do this or not, but let me know what should happen anyway.

You saw the pix in our other post of the 9" Spanish mortar, which due the different system of measures in use in Spain when this was made, is about 9.5 inches in English measure.  The two balls I have that are closest to fitting are 9.1 inches diameter.  This would leave way too much windage, a total of 0.400 in. 

If the bore had a 1/8 in. thick liner in it, the total windage would only be 0.150, (or 0.075 all around assuming the shell was centered), and I could shoot it with that.

What if I made a 1/8 in. thick aluminum liner the full length of the straight part of the bore, loaded in the 9.1-inch ball, and shot it, no epoxy or nuthin' holding the liner in?  Which of these would happen:

1.  Liner is ejected before ball
2.  Liner comes partway out and opens up like a tulip outside the muzzle.
3.  Powder gas presses the liner into bore so hard it does not move at all.
4.  Ball comes out first due to larger surface area exposed to powder gas, then liner ejects and flies a short way.

if there's any hope to this scheme, I could even make a quicky liner out of wrapped-up aluminum flashing.

I wouldn't mind cementing the liner to the bore with some adhesive that was temporary, but I don't think I'd want to use epoxy as it may damage the original bore.

Any thoughts?

I previously had decided to use maybe two layers of canvas in a bag sort of arrangement to take up the excess windage, but the liner thing seems so much neater and more positive, even if it ejects, so long as the ball gets going first.

[Cat Whisperer]

You've ID'd the posibilities.

More conventional than a liner would be a sabot.  Then you KNOW it's going to exit the barrel and you can design it so that you know where/how it's going to fly.

[cannonmn]

sabot.

Sounds like an ideal application for some kind of plastic or nylon such as used in military ordnance for rotating bands.  I guess the thing to do would be to make a sort of tall  bowl that would conform to the ball on its lower half, then conform to the bore for an inch or two,so it extends a bit above the center of the ball.  Woulldn't it be nice it there was a big PVC pipe cap that would nearly fit?

[GGaskill]

Maybe you could dip the shot in something like Plastidip that would enlarge its size.

[Rickk]

a loose aluminum liner sounds dangerous.

A sabot (wooden) sounds safer.... possibly with a thick cardboard patch around the shot to insure it stays centered. If fire season is upon you, soak the cardboard in backing soda solution to make it less likley to burn.

[lance]

 I have lots of 1/8" thick leather, easy stuff to find, can get it in different thickness too. anyway couldn't you make a liner the full length of the straight part of the bore out of leather? it will protect the bore, and won't fly far if it comes out. Hard leather that thick cuts easy on a bandsaw, if you try it.

[cannonmn]

couldn't you make a liner the full length of the straight part of the bore out of leather?

Interesting idea, although I think anything we use for a bore liner would have to be stiff enough so there's no chance of it bunching up and plugging the bore.  I can't really see any problem with using the 1/8 in. leather for some kind of sabot, that might work just fine if I can form it into a bowl-like shape. 

I probably need to visit Wal Mart and see what kind of kitchen bowls they have.  I'd hate to waste time making something if Wal Mart has anything that would work, maybe a Tupperware-like mixing bowl?

[lance]

 The hard 1/8" thick leather would be tough to form into a bowl, but would be good to form a cylinder. i have some that is almost harder to bend than aluminum. anyway, talking about bowls, what about cutting a basket ball in half? tupperware might work too, i'd be kinda worried about scraping melted plastic out of that beautiful mortar, that's if any of it melts?

[Double D]

Sabot is the only way.  Or just shoot the 9 inch balls the way they are.  They are going to fly.  They won't fly the way larger ones would but they are going to fly.

What I see with thing like tubes of Aluminum , plastic bowls, and cardboard or leather patches  is the tube and ball moving together then jaming and the mortar blowing up.

The orignal used sabots, so you should use sabots

Get yourself a sheet of plywood.   Cut out a bunch of rounds 9.25" in diameter.   In the center of some of the rounds cut a hole 3" in diameter.  Stack up these rounds with the hole  high enough to support you ball.  Now place two solid 9.25 rounds under that. Glue these together and when dry you have a sabot just like they use  in cannon.  Strap you ball to the sabot with acouple piece of masking tape.

[Cat Whisperer]

There would indeed be a bit much of windage given the original statement of the problem, but you will still get good range.  The pressure will be a little lower due to the extra windage, but looking at the AREA of the round upon which the pressure is applied you will still get good (not best) velocity.  Accuracy may be another issue.

I've seen this with my own 4.5" shooting 4-1/4" juice cans and with a Dixie 4.85" shooting 4.5" pvc.

[lance]

  Strap you ball to the sabot with acouple piece of masking tape.

Masking Tape .........GREEN DUCT TAPE, would be the only way to go

[Double D]

No! Masking tape!  You want the tape to break and the sabot to separate.  Discarding sabot you know.   The sabot is only in there to seal the bore and align the ball in the bore.

[Cat Whisperer]

But what about some of the 'vintage' ones banded with iron?

[lance]

But what about some of the 'vintage' ones banded with iron?

that's kinda what i was thinking, i figured the 90 pound ball leaning at an angle in the tube would tear loose from masking tape, then it wouldn't be centered in the bore. that's what i was thinking when i wrote green duct tape.

[Artilleryman]

In my experience the metal straps and sabots tend to come apart when used in field guns.  With a mortar I would think that if some held on and others didn't it would definitely affect the accuracy.  Having said that I haven't come across, or at least don't remember, any references to sabots for mortar shells.  (I would be interested in references about mortar sabots.)  It is hard enough to get the shell fuses to light with just the shell, I would think that it would be even harder to do so with a sabot on it.   As far as I know the only "saboted" round for a seige mortar is when a basket is made up to hold a number of smaller shells.  This was an improvement over the "stone mortar".  The effect must have been somewhat like a cluster bomb, no place to run, no place to hide.

One of the ways historically to reduce windage for garrison/seige guns was to put the projectile into paper case that the powder charge was held in.  The purpose was to improve accuracy and to prolong the life of the gun.

I am afraid I don't have any suggestions other that to patch the shell.

[Double D]

Stuff the bals in a couple brown grocery sacks...Good one Norm.

[Victor3]

 Why not just put a big wad of aluminum foil on top of the charge and ram the ball on top of it to form a sabot?

 Maybe I'm missing something here but at the end of the day, isn't the relatively small percentage difference between what the ball diameter is now, compared to what it 'should be' (if we're forced for some reason to go by a strict 1/40th) a bit of hair splitting?

[Double D]

Victor, I agree just put the 9 inchers in an shoot.

[cannonmn]

Thanks for all the good brainstorming and historical background.  We'll be putting fire in the hole hopefully before long, this weekend is too party-filled and rainy, but maybe the next.

So it looks like some kind of bag might be a minimal fix here, think I have some smallish burlap bags, also have some canvas sheets, and will at first try something easy-to-do along those lines.  The bag idea is attractive for another reason, namely that we could tie a red streamer to the open end to let us find the shell easier at longer ranges.  I've shot a bronze Turkish mortar using balls with long cloth streamers and watching them fly is kind of fun.  I keep thinking I should soak 'em in diesel and shoot 'em at night, but never tried that.  You can understand that having only two "shells" I'm a bit paranoid about losing even one.

[Artilleryman]

The further you shoot them the more likely you will lose them.  Depending on the soil and soil cover you can bury one and the hole seems to cover itself up.  I like the paper bag idea or maybe a newspaper patch.  Just make sure that you don't set a field on fire.  Paint them a bright color to help locate them if they stay on top of the ground that has grass or brush. 

[Cat Whisperer]

What about paper mache?  (as a material to make the sabot)

You could even blend in the baking soda for fireproofing.

[Double D]

The further you shoot them the more likely you will lose them.  Depending on the soil and soil cover you can bury one and the hole seems to cover itself up.  I like the paper bag idea or maybe a newspaper patch.  Just make sure that you don't set a field on fire.  Paint them a bright color to help locate them if they stay on top of the ground that has grass or brush. 

Keep your load light  so your range is short say 100 yards, so you can see them hit.

[lance]

 cannonmn, i certainly hope we get to see video of that beautiful mortar when you get time to fire it.

[KABAR2]

In the following thread one of the scenarios is answered....... he used a steel sleeve not attached...... it came out......


http://www.gboreloaded.com/forums/index.php?topic=134016.0