Beer/Soda Can Mortars?

[Aragon]

I would like to learn more about beer/soda can mortars. Not only different designs and construction techniques, but actually how to effectively shoot them. Things like:

* Aiming such a mortar?

* Different loads?

* F/FF powder differences in terms of performance?

* Distance/load/barrel elevation data?

* Preferred barrel elevation (eg. 45 degrees?)

* Any effects of barrel length?

* Shooting "standard" vs. "tall boy" cans?

* Projectile development? Weights?

Thanks for any insight into this form of shooting. Before this thread gets flooded with safety comments, please understand that I'm only addressing well-designed and well-constructed mortars that have long been proofed to be safe for operation.

 

[expat_alaska]

That may be fun, but may I direct you to anvil launching using BP? Costs considerably more than what you have ventured but very cool.

The idea is to get the top anvil to land as close to the launch site as possible. Lots of science involved.

IMO, awesome as all get out. I love it!

The local church here does pumpkin shoots and, while fun, is not at all the same thing.

https://www.youtube.com/watch?v=vP-X7nLwvVY

Sorry, not to take away from your thread..

 

[WestKentucky]

Both seem like fun. I like the idea of a soda mortar because other fun projectiles are very similar sized, or can easily be put into a csn-sabot

 

[Aragon]

Beer can mortars always seemed sorta cool to me, but nothing special -- until I tried shooting one at a target in competition. Competition always makes such things so much more fun. It was sorta like chipping at a flagstick 150 yards away. A lot of fun.

It would be great to learn more about shooting mortars...

 

[4v50 Gary]

keep it at 45 degrees and learn to adjust your powder charge

I fill my cans with plaster. I don't weigh them (but I should) and different weights results in different distances attained.

Also consider the wind. In high winds I had my cans go over 100 yards.

 

[Aragon]

That may be fun, but may I direct you to anvil launching using BP? Costs considerably more than what you have ventured but very cool.

The idea is to get the top anvil to land as close to the launch site as possible. Lots of science involved.

IMO, awesome as all get out. I love it!

The local church here does pumpkin shoots and, while fun, is not at all the same thing.

https://www.youtube.com/watch?v=vP-X7nLwvVY

Sorry, not to take away from your thread..

Interesting, but I barely have enough patience to load and shoot a mortar!

 

[Aragon]

keep it at 45 degrees and learn to adjust your powder charge

I fill my cans with plaster. I don't weigh them (but I should) and different weights results in different distances attained.

Also consider the wind. In high winds I had my cans go over 100 yards.

Have you noticed much difference in "bounce" upon landing when shot at say 45 degree vs. 60?

I wonder how big of a difference projectile weight makes? I wonder if shooting a tall-boy would be better than a regular sized can? I suspect it would weigh more but wind would also effect it a bit more as well.

 

[rcmodel]

I imagine in either case, no bouncing going on.

A 2 pound weight raining down out of the sky will generally bury itself in the ground deep enough you will need to bring a shovel.

rc

 

[Aragon]

I imagine in either case, no bouncing going on.

A 2 pound weight raining down out of the sky will generally bury itself in the ground deep enough you will need to bring a shovel.

rc

They bounce -- a lot. At least when they hit dry dirt.

 

[kBob]

Well, real mortars fired between 45 degrees and 80 degrees tend to have projectiles falling very nearly straight down.

Using the clening rod technique of counter battery is a pain in the gazzoot when dealing with mortars. With military mortars and artillery there is a tendency for the intact fuze assembly to be blown on in its pre blast course on detination. This leaves a fuze hole in the crater that can sometimes be easily seen and sometimes must be hunted for via careful dirt removal or probing. Once found a cleaning rod is inserted into this hole and on detirmines which way it is leaning and shoots an azmith back in that direction. This is transferred to a map and the gun that fired is somewhere very near this line if all is done right. One then tries to establish what type of gun fired from shell fragments. you can then mark the line at the maximum range of the gun that fired and so shorten you search area.

If you can find two such holes some distance apart (more than 500 meters is nice) you can chart them both and where the lines cross on the map, there is the gun.....maybe..... close to it.....if it has not moved.

Anyway Mortars are difficult as the rounds have generally stopped forward or down range motion and so detecting the lean on a fuze hole is usually difficult to say the least. Add to this that most mortars are fin stabilized and non spinning so the rounds wobble (why a incoming mortar round sounds like WHOOP_WHOOP WHOOP as opposed to the shriek of an incoming artillery round......the shoop shoop of artillery going over and far away doesn't sound quite like a "you are there" mortar incoming either) So the fuze may not have been pointed "properly" for your counter battery use.

In the olden days like the civil war era and further back muzzle loading mortars were at fixed elevations. Generally 45 degrees, though mortars in permanent fortifications were some times at angles to give the best coverage of a known dead zone for direct fire (low angle) artillery. hat is spaces low angle artillery can not hit, like a depression in the ground folks might take cover in. Direct fire is to shoot directly at something in low angle (less than 42.5 degrees in the atmosphere) direct lay means you can actually see what you are aiming at.

Range adjustments as noted earlier where by varying the amount and or type of powder in use......and still is although the elevation can to day be changed. For each elevation there are a number of ranges and different charges are used. Most mortar round in modern use have increment bags already attached to the shell. One consults the computer....not a machine but the man doing the computing though he may use a computer.....and finds out the best elevation setting and number of increment charges to remove from the shell for best accuracy at a given range.

In Muzzle loading days fuses were generally powder trains that were ignighted on firing. Time was set by either varing the length of the powder train or holing the side of the fuse to have the same effect. A log was kept to show time of flight to various ranges and the length the fuse should be cut to or with fixed mortars the range marked on the fuse used for specific charges.

You now know more than you ever wanted about mortars.......unless you fell asleep at your key board.

-kBob

 

[BCRider]

Kbob, your post seems to be covering the higher end of the scale for knowledge on the topic. While interesting, I did learn more than a couple of things from it, I'd suggest it's well above the level Aragorn is asking.

* Aiming such a mortar?- They are aimed by a combination of altering the angle and the strength of the charge which determines the height and shape of the arc the projectile will cover. I'd likely start with two or three basic elevation angles such as 40, 50 and 60 degrees. Or since it's a mortar perhaps even 50, 60 and 70 degrees. After all the idea here is sort of like in golf. The player in golf when faced with a short shot to get onto the green does not use a low angle club and pull their swing. That leads to disaster. Instead they opt for a strong angle to the club to lob the ball up so the regular and well practiced swing vents its energy into making the ball go up instead of out. A mortar uses the same principle. From there I'd come up with a few charge volumes/weights. If it helps think of it as water from a nose nozzle. You can control the point of landing of a constant power stream by altering the angle to extend or close in the landing. Or you can use a fixed angle and vary the strength of the flow to arc it into the right spot. Either way it'll be YOUR mortar with YOUR weight of projectile. This means that unless your mortar turns out to be very similar to someone else's that you're on your own for developing the ballistics data.

* Different loads?- See above. Different power loads are essential to setting your range. You'll likely come up with pre-measured loads to be used with preset elevation angles for the common distances of 50, 100 and 200 yards. Or, more likely, since you'll be shooting at bed sheet or tarp targets laid ON the ground instead of stapled to the backing boards at the berms you'll more likely be looking at 75, 150 and 250 yard increments so the flat targets on the ground sit on the flat areas between the stop berms. It all depends on where you're shooting. For the longer range shots you'll likely use the 40 or 50 degree angles. But since it's a mortar I don't see going any more horizontal than 40 degrees as something you really want to do. Otherwise it verges on just being another short cannon.

* F/FF powder differences in terms of performance?- For filled soda cans I think you're looking more at F or Cannon grade powder. FFg would be finer than you want to use at this size. The coarser grades have a slightly slower burn so they are more suitable to larger charge weights.

* Distance/load/barrel elevation data? - Covered in the previous points. You'll just have to develop your own data for each different style and weight of projectile.

* Preferred barrel elevation (eg. 45 degrees?) - See above. I'd certainly use at least two angles. And three angles gives you a little more room to play. I'd also suggest that these are indexed angles that "lock" into place as opposed to a full range where you risk being off by a degree or two. Or if you want a number of options then use a fairly coarse tooth gear as your angle indexer with a settable finger that locks into the tooth. That gives you a lot more angles to play with but still ensures that each selection can be closely repeated.

* Any effects of barrel length? - It's a mortar. And for the classic front loaders that means you're looking at a bore length of around 3 to perhaps as much as 4 bore diameters. Much longer and it moves into being a different category of field piece.

* Shooting "standard" vs. "tall boy" cans? - Since this piece will not have the benefit of rifling I'd suggest that the closer you can get the projectile to resembling a ball the better. That suggests the stubby half size soda cans. And perhaps even something like mortar or plaster filled tennis balls used with some bed sheet as a patch to get a good snug non rolling fit in the bore. Otherwise you're looking at a lot of tumbling from the longer shapes. But one cannot overlook the ease of obtaining shells for the projectiles if one sticks to the common as dirt 10oz beverage size of can. So I'd likely start with regular pop/beer cans and run trials with the stubby cans and tennis balls to see if there's any real world improvement. The stubbys and tennis balls would also have the advantage of not requiring as much powder per shot to reach a given distance. So that's something to consider too.

* Projectile development? Weights? - Weights will be fixed by the size of the projectile shell that you then fill with whatever cheap filler you can find to use. I'd suggest that mixing your own playgound sand and portland cement is going to be the cheapest possible filler. To keep things consistent find a suitable bucket and run "scraped top" loads of sand to portland along with the same bucket used to measure the water needed to get to a runny but not liquid sort of mix. Consistency from mix to mix will be essential to ensure that the fills are good and consistent. And to avoid the mixture drying out and reducing the weight of the projectiles I'd even suggest storing them in a small garbage can full of water once the mortar fill has cured for a few days. At that point the water won't hurt the mortar at all. And it'll ensure the water in the motar can't dry away and alter the projectile weight. Once you're within a day or two of using them it's fine to take them out and let the cases dry. Particularly if you're using tennis balls with the fluffy outside.

I don't have my own mortar.... YET.... But it's very much on my "To Do" list. And perhaps the things I've posted suggest that I've obses.......er.... given a fair degree of consideration.... yeah, that sounds better.... to my options. Hopefully it helps point you in the right direction.

Oh, and from all the stuff I've seen live or on You Tube I think you'll be surprised at just how little powder it takes to lob a mortar filled pop can out to 100 or so yards. Start small with around 20 grains and work up from there. Locally a guy with a golf ball cannon regularly bounces them off the hillside at 240 yards at my club's range with only 20 gns of FF and using about a 15 to 20 degree elevation angle. So it's quite possible that you'll find that 20gns will end up working for a close in 50'ish yard load depending on what projectile you use.

 

[CANNONMAN]

Mortars are almost as fun as a cannon, but not really. Watch out for what BCRider and that KBob guy tell you. Or else your apt to learn stuff! I asked a few of these questions here a bit ago and the only thing I find missing is the aiming part. The actual manner in which they were aimed in the civil war is a fastening study. If you find my thread or ask these folks to find it for you on how to aim a cannon, I believe you'll find the pics and accounting. If memory serves, three guys: one gave orders and the other two obeyed them. The two had poles called...[?] and the mortar had a slot on each side that the poles fit into to turn the mortar. You have left and right @ a 45. Your distance is a function of ammo and charge. Note that there exist a maximum height and distance attainable. More and finer powder packed tighter will not change this. Skill and awareness for the variables you are able to control will render you a better shot. PS, the smaller can lessens the variables. If your ever by this way... I toss the gauntlet and you are charged to a mortar dual!

 

[Aragon]

* Aiming such a mortar?- They are aimed by a combination of altering the angle and the strength of the charge which determines the height and shape of the arc the projectile will cover. I'd likely start with two or three basic elevation angles such as 40, 50 and 60 degrees. Or since it's a mortar perhaps even 50, 60 and 70 degrees. After all the idea here is sort of like in golf. The player in golf when faced with a short shot to get onto the green does not use a low angle club and pull their swing. That leads to disaster. Instead they opt for a strong angle to the club to lob the ball up so the regular and well practiced swing vents its energy into making the ball go up instead of out. A mortar uses the same principle. From there I'd come up with a few charge volumes/weights. If it helps think of it as water from a nose nozzle. You can control the point of landing of a constant power stream by altering the angle to extend or close in the landing. Or you can use a fixed angle and vary the strength of the flow to arc it into the right spot. Either way it'll be YOUR mortar with YOUR weight of projectile. This means that unless your mortar turns out to be very similar to someone else's that you're on your own for developing the ballistics data.

I was actually looking for information on actual sights. Most competitors just "eyeballed it" and then continued to kick their mortars to adjust for "windage" or a crank or two on a Heim end for elevation.

I believe the maximum angles are 40 and 60 degrees in competition. I would likely try to develop data at 45 and 60 degrees, from 50 to 150g in 5 g increments. 60 degrees would be better because the projectile would bounce and/or skid less, but the wind would also have greater influence on shots taken at that angle.

* Different loads?- See above. Different power loads are essential to setting your range. You'll likely come up with pre-measured loads to be used with preset elevation angles for the common distances of 50, 100 and 200 yards. Or, more likely, since you'll be shooting at bed sheet or tarp targets laid ON the ground instead of stapled to the backing boards at the berms you'll more likely be looking at 75, 150 and 250 yard increments so the flat targets on the ground sit on the flat areas between the stop berms. It all depends on where you're shooting. For the longer range shots you'll likely use the 40 or 50 degree angles. But since it's a mortar I don't see going any more horizontal than 40 degrees as something you really want to do. Otherwise it verges on just being another short cannon.

We shoot at golf flag sticks.

* F/FF powder differences in terms of performance?- For filled soda cans I think you're looking more at F or Cannon grade powder. FFg would be finer than you want to use at this size. The coarser grades have a slightly slower burn so they are more suitable to larger charge weights.

F is cannon grade...

* Distance/load/barrel elevation data? - Covered in the previous points. You'll just have to develop your own data for each different style and weight of projectile.

Yeap.

* Preferred barrel elevation (eg. 45 degrees?) - See above. I'd certainly use at least two angles. And three angles gives you a little more room to play. I'd also suggest that these are indexed angles that "lock" into place as opposed to a full range where you risk being off by a degree or two. Or if you want a number of options then use a fairly coarse tooth gear as your angle indexer with a settable finger that locks into the tooth. That gives you a lot more angles to play with but still ensures that each selection can be closely repeated.

Yeap.

* Any effects of barrel length? - It's a mortar. And for the classic front loaders that means you're looking at a bore length of around 3 to perhaps as much as 4 bore diameters. Much longer and it moves into being a different category of field piece.

Still I'm curious how a 7" barrel would differ in performance from a 10" barrel? Similar to a longer gun barrel -- more time to burn powder?

* Shooting "standard" vs. "tall boy" cans? - Since this piece will not have the benefit of rifling I'd suggest that the closer you can get the projectile to resembling a ball the better. That suggests the stubby half size soda cans. And perhaps even something like mortar or plaster filled tennis balls used with some bed sheet as a patch to get a good snug non rolling fit in the bore. Otherwise you're looking at a lot of tumbling from the longer shapes. But one cannot overlook the ease of obtaining shells for the projectiles if one sticks to the common as dirt 10oz beverage size of can. So I'd likely start with regular pop/beer cans and run trials with the stubby cans and tennis balls to see if there's any real world improvement. The stubbys and tennis balls would also have the advantage of not requiring as much powder per shot to reach a given distance. So that's something to consider too.

12 ounces are most common around here.

* Projectile development? Weights? - Weights will be fixed by the size of the projectile shell that you then fill with whatever cheap filler you can find to use. I'd suggest that mixing your own playgound sand and portland cement is going to be the cheapest possible filler. To keep things consistent find a suitable bucket and run "scraped top" loads of sand to portland along with the same bucket used to measure the water needed to get to a runny but not liquid sort of mix. Consistency from mix to mix will be essential to ensure that the fills are good and consistent. And to avoid the mixture drying out and reducing the weight of the projectiles I'd even suggest storing them in a small garbage can full of water once the mortar fill has cured for a few days. At that point the water won't hurt the mortar at all. And it'll ensure the water in the motar can't dry away and alter the projectile weight. Once you're within a day or two of using them it's fine to take them out and let the cases dry. Particularly if you're using tennis balls with the fluffy outside.

Weights will also depend on the filler. Some use lead shot as aggregate with their concrete mix.

Oh, and from all the stuff I've seen live or on You Tube I think you'll be surprised at just how little powder it takes to lob a mortar filled pop can out to 100 or so yards. Start small with around 20 grains and work up from there. Locally a guy with a golf ball cannon regularly bounces them off the hillside at 240 yards at my club's range with only 20 gns of FF and using about a 15 to 20 degree elevation angle. So it's quite possible that you'll find that 20gns will end up working for a close in 50'ish yard load depending on what projectile you use.

We were getting very close to the flag stick with 65g the other day...

 

[WestKentucky]

Aiming a mortar? AIMING it? I consider such to be an impossible task. You can very well point it in the right direction and make a well educated guess as to the powder charge needed but when flight time is measured in whole seconds and your projectile is vertical upon impact you don't really have much control. Your hoping for consistent wind and a true angle of departure.

On that note, it is exactly my cup of tea. You build something by hand, shoot massive projectiles out of it, and the objective is to hit something but know good and well that your going to settle for much less than perfection.

 

[Aragon]

Aiming a mortar? AIMING it? I consider such to be an impossible task. You can very well point it in the right direction and make a well educated guess as to the powder charge needed but when flight time is measured in whole seconds and your projectile is vertical upon impact you don't really have much control. Your hoping for consistent wind and a true angle of departure.

On that note, it is exactly my cup of tea. You build something by hand, shoot massive projectiles out of it, and the objective is to hit something but know good and well that your going to settle for much less than perfection.

Mortars definitely may be aimed...

 

[CANNONMAN]

Your pic is really interesting. And of course your right. The mortar you show, is this what you intend to shoot aluminum cans and concrete out of? Are you planning on applying fletching to your cans? Is your end goal to create a "dart"? Does anyone else in the competition shoot the item you show? If so, Why the questions when everything about the item you show has an answer to the questions you pose? And why are you folks not hitting the target with rapidity? By crude definition of beer can mortar -v- your pic these two are distant kin. Other than optics how to aim a mortar. Depends on your math skills. I know of at least three members of this site who know how this is done. I personally refuse to elaborate as I fell it is counterintuitive to the "sport".

 

[4v50 Gary]

Aragon - the bounce depends on how wet or dry the range is. On a hard surface, it can bounce or tumble a few feet and the roll to a stop. Note: Not all my cans were filled consistently. Some of the plaster had air gaps in them. A can that had a void could partially collapse on impact. I had a few tall cans too but don't recall the results.

The issue of aimed mortars came up. Yes they may be aimed and during the Siege of Petersburg some Confederates became very good with their mortars. They got good at dropping shells in a known rifle pit or foxhole. Other soldiers armed with rifles stood by to shoot any Yankee who jumped out of his pit.

BTW, my powder generally 1 cartridge case FF (7.62 x 54 Russian or similar case) for 30-40 yards, 2 cases for 70 and 3 cases for 100. Mind you, the wind plays a huge factor in this and plaster filled beer cans aren't the best projectiles out there.

 

[Aragon]

Your pic is really interesting. And of course your right. The mortar you show, is this what you intend to shoot aluminum cans and concrete out of? Are you planning on applying fletching to your cans? Is your end goal to create a "dart"? Does anyone else in the competition shoot the item you show? If so, Why the questions when everything about the item you show has an answer to the questions you pose? And why are you folks not hitting the target with rapidity? By crude definition of beer can mortar -v- your pic these two are distant kin. Other than optics how to aim a mortar. Depends on your math skills. I know of at least three members of this site who know how this is done. I personally refuse to elaborate as I fell it is counterintuitive to the "sport".

"Fletching", no. More accurate means of aiming than I have witnessed so far? Yes, perhaps.

 

[Aragon]

Aragon - the bounce depends on how wet or dry the range is. On a hard surface, it can bounce or tumble a few feet and the roll to a stop. Note: Not all my cans were filled consistently. Some of the plaster had air gaps in them. A can that had a void could partially collapse on impact. I had a few tall cans too but don't recall the results.

The range (a skeet/trap range) we shot on last weekend was dry dirt. The cans didn't bounce/tumbled/skid for a "few feet" -- well maybe a few did. Most bounced far further than that upon impact -- and the angle of the shot didn't seem to make a huge difference which surprised me.

 

[H&R Glock]

Home made from scrap mortar

Has anyone ever built one out of scrap that can be found in the junkyard???
For those of us without a lathe, welder, and milling machine, this would be handy to know.
About how much black powder does it take to launch a concrete filled soda can 100 yards downrange?

 

[BCRider]

I was actually looking for information on actual sights. Most competitors just "eyeballed it" and then continued to kick their mortars to adjust for "windage" or a crank or two on a Heim end for elevation.

If you stop to consider the geometry of the angled barrel I think you'll quickly realize that you need some way to make sure that the barrel is not tilted at all to either side to within a very tight tolerance. Any tilt will render a windage aiming sight of any sort almost a waste of time. But if you do include a plumb bob or bubble level in the sighting body then you could use a sight to provide for windage corrections.

Note that I said "windage aiming". Because of the vertical nature of the trajectory you're working with the angles for "elevation". So a simple setup such as a tube with two wires that you use for setting the windage is all the sight you need. And perhaps a small mirror set at 45 degrees so you can look down into the windage sight instead of having to just about lay on the ground. It would end up being similar to the one on the military setup.

F is cannon grade...

which makes it more suitable for a soda can mortar I recon. There's no doubt that FFg could be used but I suspect that others will confirm my thinking that it's going to be at the limit if not stretched beyond what it is normally used for in the case of your mortar.

Still I'm curious how a 7" barrel would differ in performance from a 10" barrel? Similar to a longer gun barrel -- more time to burn powder?

Well, certainly a longer bore gives the gases a longer time to work at accelerating the can. So that can only allow it to do more with the same charge. I was thinking that you were looking at a historical shape. But since I now know from your follow up posts that this is to be used in a competitive match situation that's a whole other cantaloupe! ! ! ! By all means make it 10" or even 14" to get more velocity from the charge and to give you more length to aid in mounting it to a support and aiming structure.

We were getting very close to the flag stick with 65g the other day...

Again you didn't let us know that you have others with experience in your area to base your own efforts on. So my numbers were based on starting overly safe and sneaking up on the sort of charge you need to accomplish the task. Since you have guys doing this in your area already of course you're going to work around their charge information.

You've also likely got some idea of the wall thickness of the Schedule X tube that they are using. Can you share that with us?

From looking at a pipe schedule chart I'm going to guess that they are using nominal 3 inch Schedule 160 pipe for the barrel. This size has an OD of 3.5" with a wall thickness of 0.437" which means it's a bore of 2.626 which is just about a dandy sliding fit on a pop can. Especially one that may have swelled out a little as the concrete cures. That sound about right from what you saw?

Has anyone ever built one out of scrap that can be found in the junkyard???
For those of us without a lathe, welder, and milling machine, this would be handy to know.
About how much black powder does it take to launch a concrete filled soda can 100 yards downrange?

Unless your local junk yard has large stocks of Schedule 160 or bigger pipe laying around I'd say that you won't be able to make this happen.

The problem is that as the size of the tubing goes up the ability of the pipe to contain high pressure requires massive increases in wall thickness. It's one of those exponential or square relationships. So to contain the pressure from anything up to around a 100gn charge I sure would not want to see anything that is very much less than the 0.437 inch of drawn seamless steel to hold that pressure.

And then there's the need to plug the breech. You don't just buy a cast iron cap and screw it on. You need a pretty stout breech plug that is either threaded to go into a threaded end of the tubing or you need to get it welded. And for safety's sake it would be a deeply "V"ed out joint with multiple passes to hold back the pressure.

So all in all I just don't see this working out unless you've got a pretty fancy scrap yard nearby that deals in rather heavy duty stuff.

 

[Pete D.]

Mortars

I own three BP mortars....smaller than what is being discussed...golf ball size.
One I made myself from DOM tubing and steel rod. The other two are from professional manufacture.
What they all share is that the thickness of the metal at the breech, around the powder chamber is substantial...three times the diameter of the chamber itself.
Actual barrel length is two to three times bore diameter.

About using patches....not something that I do. As I understand the ballistics involved, patching is unnecessary and may even be dangerous. BP Mortars (and cannons, iirc) use barrels that have a bore slightly larger than the projectile....this extra is called "windage" (not to be confused with that term when it is applied to the right/left adjustments made when aiming). Patching would take away the windage of the barrel and raise pressures.

Bore diameter including windage is calculated as 25/24ths of projectile diameter.

 

[Aragon]

Has anyone ever built one out of scrap that can be found in the junkyard???
For those of us without a lathe, welder, and milling machine, this would be handy to know.
About how much black powder does it take to launch a concrete filled soda can 100 yards downrange?

About 50-100 grains...

 

[Aragon]

If you stop to consider the geometry of the angled barrel I think you'll quickly realize that you need some way to make sure that the barrel is not tilted at all to either side to within a very tight tolerance. Any tilt will render a windage aiming sight of any sort almost a waste of time. But if you do include a plumb bob or bubble level in the sighting body then you could use a sight to provide for windage corrections.

Of course. The shot distance would have to come from historical testing of the mortar at different barrel elevations and powder loads. The the windage aim is what I'm interested in.

Note that I said "windage aiming". Because of the vertical nature of the trajectory you're working with the angles for "elevation". So a simple setup such as a tube with two wires that you use for setting the windage is all the sight you need. And perhaps a small mirror set at 45 degrees so you can look down into the windage sight instead of having to just about lay on the ground. It would end up being similar to the one on the military setup.

OK. NB: "windage" in cannon terminology means the clearance between the projectile and the ID of the barrel.

which makes it more suitable for a soda can mortar I recon. There's no doubt that FFg could be used but I suspect that others will confirm my thinking that it's going to be at the limit if not stretched beyond what it is normally used for in the case of your mortar.

Most sanctioning bodies require F in such applications.

Well, certainly a longer bore gives the gases a longer time to work at accelerating the can. So that can only allow it to do more with the same charge. I was thinking that you were looking at a historical shape. But since I now know from your follow up posts that this is to be used in a competitive match situation that's a whole other cantaloupe! ! ! ! By all means make it 10" or even 14" to get more velocity from the charge and to give you more length to aid in mounting it to a support and aiming structure.

I wonder if a formula exists for calculating mortar/cannon barrel lengths?

You've also likely got some idea of the wall thickness of the Schedule X tube that they are using. Can you share that with us?

For the barrel itself, Schedule 80 (.375 wall) of a seamless/weldable mild steel is more than sufficient (although that would create a safe but physically light mortar which not everyone would like.) However for the actual 1" diameter chamber (a machined and welded plug internal to the barrel) the effective wall diameter is (3.5-1) = 1.25" -- Very thick where it needs to be.

If someone were to simply weld a flat plate to the end of a piece of pipe it would take a 5.5" diameter pipe to yield the same wall thickness. Such pipe would still need to be reamed (its nominal ID is 2.5") and it weighs #64/foot.

From looking at a pipe schedule chart I'm going to guess that they are using nominal 3 inch Schedule 160 pipe for the barrel. This size has an OD of 3.5" with a wall thickness of 0.437" which means it's a bore of 2.626 which is just about a dandy sliding fit on a pop can. Especially one that may have swelled out a little as the concrete cures. That sound about right from what you saw?

The ID is just fine. You'll have to clean less if you use a nominal of 2.75"

Unless your local junk yard has large stocks of Schedule 160 or bigger pipe laying around I'd say that you won't be able to make this happen.

You can buy such pipe by the foot online. It's not cheap and the shipping is fairly punishing but nothing compared to a full hog-out.

The problem is that as the size of the tubing goes up the ability of the pipe to contain high pressure requires massive increases in wall thickness. It's one of those exponential or square relationships. So to contain the pressure from anything up to around a 100gn charge I sure would not want to see anything that is very much less than the 0.437 inch of drawn seamless steel to hold that pressure.

This relationship is given in equation form with Barlow's Formula which relates the internal pressure that a pipe can withstand to its dimensions and the strength of its material.

P= (2St)/(D)

where:

P = pressure
S = allowable stress
t = wall thickness
D = outside diameter

And then there's the need to plug the breech. You don't just buy a cast iron cap and screw it on. You need a pretty stout breech plug that is either threaded to go into a threaded end of the tubing or you need to get it welded. And for safety's sake it would be a deeply "V"ed out joint with multiple passes to hold back the pressure.

It should be welded...

So all in all I just don't see this working out unless you've got a pretty fancy scrap yard nearby that deals in rather heavy duty stuff.

Very difficult to get around all welding and machining.

 

[oneounceload]

In college we made them from tennis ball cans taped together. We could launch a tennis ball at the girls' dorm across the street easily using only lighter fluid.....BP would be interesting though.......