Removeable liners and electric firing

[cannonmn]

I have at least one old cast iron cannon that I'd like to shoot but don't want to destroy its historical value by installing a permanent liner.  It occurred to me that I might be able to make a proper 3/8" (or thicker if required) liner and insert it with enough temporary fastenings to retain it in the original bore during firing, and be able to remove it later to revert to antique-ness.

My idea to avoid vent issues was to fire it electrically using an electric match in the charge and thin insulated, dual-conductor wire out the muzzle.  There's no problem with getting that to work as long as wires are less than the windage.  The intent would be for very slow fire, like one round every half-hour, which is about what we do anyway if we let Ed go downrange and excavate the projectile after every shot.

The firing device would be a standard commercial blasting machine that has no power to the terminals until the fire button is pressed (or plunger pushed down, whatever.)  This is safer than batteries.  Electric firing is used a great deal in things like 1812 Overture with cannons, where the shots require precise timing.

One issue with the liner that does not fit tight in the bore is that it would have to be capable of firing the load with no wall support against deforming, from the actual cannon.

There are some other pieces which were spiked long ago and could be fired with the same type of system.

Whatcha think?

[RocklockI]

I've done it with my 2.25" SBR Cohorn .

It was a burgler alarm idea that worked just fine with over 100 .32 balls and some odd thousand or two BBs


A serated V8 juice taped up with a cardboard disk .

I used an Estes rocket igniter and a balloon for 'long term trapage'

I couldnt bring myself to actually set it ....but as someone and I were feuding........to the point of the Scottish game of Murder in the dark .

I thought it 'might come in handy sweeping across the front of my house and in close in too to make sure and say hello to anyone on my front porch...it .

But it did work so good I was kinda scared of the thing . BTW I'd have to explain this behaviuor to the entire north side of my St . to why are there holes everywhere ! Oh yea and the cops too .






 

[dan610324]

electrical firing wouldnt be any problem with a smoothbore
but to have a liner without any support from the main barrel could give you problems
what bore size is it ??
the larger the more possible that it will expand and get stuck in the bore

as you want to use a liner I suppose that the bore isnt in such a good shape
cast iron and powder residues "eat" up the bore quite quickly
so it could be larger in diameter somewhere down the bore then it is in the muzzle
if then the liner expands your in deep (censored word)

[GGaskill]

It depends on what the existing bore diameter is and what you want to use in the liner.  Let's look at an example.

Say you have a 6 pounder (bore diameter 3 5/8" more or less), a 3/8" liner would take you to 2 7/8" bore.  Assuming a chamber pressure of 10,000 psi, the hoop stress in the liner would be 43900 psi which is approaching the nominal tensile strength of mild steel.  The stress value is directly related to chamber pressure so if that is 25% higher, the stress is 25% higher.

If we reduce the liner bore diameter to the forum recommendation of 1/3 of the overall diameter, that would give us a bore of 1.2" and a corresponding hoop stress value of 12,500 psi, which would easily be contained by the liner alone.

Now if you had to have a 3" bore, you could have the 1.2" chamber and still be OK.

[subdjoe]

Hmmmm.....make up a barrel within a barrel. Make up a bunch of them for quick change. Have a limber chest filled with pre-loaded inserts.  

Puts me in mind of a guy I knew who was seriously considering making a new cylinder for his BFR that was chambered in 500 magnum.  He was thinking of making one chambered in .22 short, he figured that with the length of the cylinder, he could have about two inches of rifled barrel in front of the .22 short, and it should travel straight down the half inch bore/  

[Double D]

Every time this term comes up I ask for an explanation

Hoop pressure is a static constant pressure.  Chamber pressure is an accelerating/decelarating pressure, how do they equate?

Can a steel have greater hoop strength than burst strength?

[GGaskill]

Taking steel as a material, there is no such thing as "burst strength."  You have tensile strength (pulling the steel apart), compressive strength (pushing the steel together) and shear strength (which some will argue is just tensile strength from a different perspective.) 

Taking a cylindrical piece of steel such as a pipe, it bursts when the tensile strength of the material is exceeded due to internal pressure but the relationship is not one to one.  The amount of steel resisting the pressure is a major factor in what the internal stress is.  So a thicker wall has more material to resist and therefore its stress is less than a thinner wall.

This is basically the same as taking a 1" square bar and hanging a 1000 lb weight from it.  The stress will be 1000 psi.  If we hang the same 1000 lbs from a 2" square bar, the stress will be only 250 psi because there is four times as much material carrying the load (2" x 2" = 4 sq in.)

The explosion of a powder charge is a dynamic event but it does reach a maximum and that is the number we use in calculating the stress in the metal.  Most of the time the stress is less than that calculated but, since we can't change the thickness of the gun barrel in response to the changing stress, it is overbuilt for the times when not resisting maximum pressure.

[cannonmn]

Thanks for the thoughts and sample calculations.  I wasn't thinking the inserted bore would have to be so small but you can't escape the laws of physics.

Think I'll content myself with firing occasional blank charges in the original bore, with long fuse and no one within fragging range of the cannon.

[Cat Whisperer]

Getting back to the original question -

John - have you determined what to hook up to the blasting machine?

(I have a 10 cap machine - twist handle on the top, much handier than the 50 cap (the big wooden box)).

One could hook up an ingnition system through the vent hole, and make it seal as well.

I'm looking for something that would be very economical and easy to build.

[cannonmn]

1.  John - have you determined what to hook up to the blasting machine?

2.  One could hook up an ingnition system through the vent hole, and make it seal as well.

1.  Not sure I unnershtan da queshun.  The most direct answer is "two wires leading to the two short wires coming off an electric match."

2.  Yes, agree.


The electric thing was only mentioned in the context of having either a spiked vent or no vent.  I see what you are getting at though, one could take a thin wood dowel and mount an electric match on the end of it, so long as it would all pass thru the vent.  Then you'd have something you could insert in the vent much like a friction primer-instead of a lanyard coming from it, you'd have a pair of wires.

Many blasting machines now are cigarette-pack sized and electronic vice the old electromechanical kinds.  My company sells one piezoelectric type which has a one-cap capacity, it is cigarette-pack sized, runs $125. on sale.

[MikeR C]

GGaskill,
What you wrote makes sense, pick a material of whatever strength and make it of whatever thickness to resist the maximum pressure predicted, that would be below yielding point. Add something for a safety margin and you have a safe barrel.
Do you take into consideration rise time to max pressure or is there a constant or rule of thumb? It seems to me that the quicker the rise time the more problems it would cause...

Thx
MikeR C

[RocklockI]

Where do you buy electric matches ?

[cannonmn]

Where do you buy electric matches ?

Since 9-11 they have become a controlled item for obvious reasons.  Fireworks suppliers may stock them but you will need an FFL to purchase I think.  A lot of folks make them at home-there's some goop you dip the ends of an insulated wire pair into (like speaker wire) and once it dries, the stuff is conductive, resistive, and also somewhat explosive, so tickle it with some juice and pop!

I'm guessing a bit of 0000 steel wool at the end of two wires may work OK if surrounded by some FFFF or FFF, but I haven't tried that, and don't know how much juice is required.

"bzzzz, pop, BOOM, Owww!!!"

"Mama I smell smoke and what're those funny noises?"

"Oh honey don't worry that's just Uncle Gary out in the garage playing with his electric matches again."

[Double D]

Google Electric match and you will a lot of hits on them...

[RocklockI]

Well you 'can' use an Estes rocket ignighter(sp) .

It's just a fine nichrome wire . The use long nichrome wire with current running through it . I helped a gu once cut large laminated blocks of foam to biuld a Rutan Veryeasy .

They get hot with a template on easch side of the block then you carfully omve the ends of the wire together and cut out a perfect airfoil .

If you ever made the mistakenly touched a piece of speaker wire from a car battery terminal to the chassis . It get blazing aze hot real quick .

I'd try a nichrome wire bent in half and dip the bent part into a bp mush the dipp that into some fine powder ? The main issuse is making darn sure you dont short out the wires accedentaly .

[Victor3]

Thanks for the thoughts and sample calculations.  I wasn't thinking the inserted bore would have to be so small but you can't escape the laws of physics.

Think I'll content myself with firing occasional blank charges in the original bore, with long fuse and no one within fragging range of the cannon.

 Why not make the liner using a plug that has a reduced chamber bored into it to get the required wall thickness? The rest of the liner could have a pretty thin wall, and you could make the chamber long enough to get a goodly amount of powder into it.

[cannonmn]

Why not make the liner using a plug that has a reduced chamber bored into it to get the required wall thickness? The rest of the liner could have a pretty thin wall, and you could make the chamber long enough to get a goodly amount of powder into it.

Thanks for the ideas.  Now I'm going to focus on one cannon at a time, since the various weapons have various capabilities/limitations.  I think the next one to consider for this stuff is Vicky, the wrought iron and steel British 16-pounder rifle.  Her basic problem is a big, firmly-planted (I guess) spike, so that's why electric firing was of interest.  With this gun, given the heavy construction with steel barrel and wrought-iron jacket around it, there's no need for a sleeve.  I've decided to flip her upside-down and raise the muzzle a bit over horizontal, then pour some penetrants in the muzzle, which will run down the bore and soak in around the spike.   After allowing enough time for penetration (at least some days) flip her over again, weld some square cross-section stock to the protruding spike, and try and revolve it then remove it.  If the spike can't be removed, then we go to electric firing.  We'll shoot first with canister since it is very easy to make as opposed to a proper projectile which will take the rifling etc.

[KABAR2]

Couldn't an EDM be used to burn out the spike in Vicky?  then you could return her to regular service....

[RocklockI]

If it doesnt come out why not drill it out ?

This electric firing is abit esoteric isn't it ?

Gary

[cannonmn]

Couldn't an EDM be used to burn out the spike in Vicky?  then you could return her to regular service....

I guess I'm He!!-bent on firing the thing electrically as an experiment, so I'll make my 0.5-azz try at removing the spike with penetrants, welding attachment to it, etc.,. then when none of that works, I will do some electric-fired shots.  I mean why not, we burn up lots of friction primers and fuse, time for trying ignition method no. 3, doncha think?

[RocklockI]

John , if you cant get the spike out , then will you break it off inside 

You wouldnt seat your insert on the evil end of the spike would you ?

Gary

[cannonmn]

if you cant get the spike out , then will you break it off inside

It isn't a real military old-timey cannon spike, it is something someone put in in 20th C. to disable it.  I don't think it protrudes inside the chamber at all. 

Also I gave up on lining this piece with anything since the gun already has a thick steel tube inside a wrought iron jacket, and doesn't need a sleeve. 

[dan610324]

now you made me curious John
what kind of cannon is it ??
any photos ??

[cannonmn]

now you made me curious John
what kind of cannon is it ??
any photos ??

Dan this is the British 16 pdr. rifle I had a discussion about back about Sept.  I'd be able to find it for you if there was a working search function on the site, however....

[KABAR2]

Dan,

Here is a link to Vicky and a photo.

http://www.gboreloaded.com/forums/index.php/topic,181519.msg1098882113.html#msg1098882113

[RocklockI]

I remember Vickey now . Wern't these British made Indian or Nepolise pieces ? 

John honestly , you should get that vent clear and shoot it normaly.

Burn it out with an EDM (worst case) . Drill it out . Drive it out into the bore ,then dump of course .

WHATEVER it takes ...give up on this liner thinnggyage .

What would you achieve ? something thats goes ..."pop..." and some 'lame ball' faulters towards ...the ground anyway ?

This is a rifle Sir ....

GET the VENT clear ! Then carry on ,per normal .

Gary

This is as always (faines youmillity ) my humble opine . And as always ...I could be wrong .......eh no ...I'm right .

Nice gun BTW

[Double D]

Dan this is the British 16 pdr. rifle I had a discussion about back about Sept.  I'd be able to find it for you if there was a working search function on the site, however....

Go to search put  in "British 16 pdr" and make sure it is in quotes, put in the user cannonmn and then search, You will get one hit Drawings and details, British 16 pdr. RML Mark I, L.S.  

[cannonmn]

you should get that vent clear and shoot it normaly.

Mama, that mean ole' Gary's trynna take away my excuse to play with electric firing.   Make him stop it!

[dan610324]

isnt it enough clearence / depth in the grooves to have thin wires there ??
it would be much more interesting to see some shooting results from it in full bore size useing the grooves
would it be possible and safe to shoot patched spherical balls in such an cannon ??
maybe a thick greased leather patch could engage the grooves much enough to get some accuracy

[RocklockI]

you should get that vent clear and shoot it normaly.

Mama, that mean ole' Gary's trynna take away my excuse to play with electric firing.   Make him stop it!

Stop it ! I am encouraging you John , nonsence by all means play  !  (Led Zepplin LOUD )
Electricly fired 'stuffagge' is a blast .

It's just that cannon 'could do so much ,,     so much .'

gary