Improving Accuracy of "Tin Can" Mortar Projectiles

[seacoastartillery]

     Mike and I have long wondered if the variable accuracy of "tin can" mortar projectiles can be improved.  As we have NOT done any experiments beyond a simple 'Rope Tail' which didn't work, we have a genuine interest in knowing if any of you have found a way to improve the flight characteristics of these simple rounds, and thus improve your mortar's accuracy. 

     We are also wondering if the KISS, (Keep it simple stupid) Principle should be rigorously applied, or are there fairly inexpensive 'High-Tech' projectile improvements to be made?  All these should really be tested with a batch of carefully made mortar balls to see which of these basic types wins the accuracy race.  We will delay this until we have a proper mold to cast some 2.66" dia. balls, probably from zinc.

     I sketched out a  'Delayed-Deployment, Shuttle-Cock Guidance Assembly'  this past week and purchased a few simple parts from which to make it.  It will be tested this coming Saturday, March 20th.  We are using the long #2 steel Asparagus can for all our experiments to have at least one constant among all the variables.

Anybody?

Mike and Tracy

[Cat Whisperer]

Excellent question.

Of noted experience are those that have done well in mortar bingo competition.

So this is going to require some notetaking to determine WHAT the accuracy is, and then note things changed that make it better or worse; coming up with a list of items that affect accuracy.

[Victor3]

 Hey, medi-okra (a little canned vegetable humor there) minds think alike. 

 Since learning that steel soup cans fit my mortar, I've been thinking on adding fins somehow. Kinda hard to 'splain without pics, but...

 Say you made three .015" flat spring steel shims, ~3/4" x 3" and pop-riveted them 120 degrees apart with 2.5" sticking past the bottom of the can.

 Now bend/twist the protruding ends of the shims to form fins that would impart spin to stabilize the can in flight.

 The fins, pushed in toward the center of the can for loading, would pop out past the OD of the can as it left the mortar.

 Should work better with a light projectile & charge with the majority of the weight at the front of the can. You could fill the bottom 2/3 of the can with that urethane spray foam stuff and pour concrete on top.

[Cannoneer]

Alright, now everything is as it should be in BPMC-land! Victor has returned from a survivalist test out in the bush, and he's evidently come back in the full swing of things. That's right folks, you read it correctly, he's now contemplating attaching fins to a soup can.   Cat will be along in a minute, and they'll start discussing the most efficacious way of accomplishing this fantastic engineering feat.
Welcome back buddy!

[little seacoast]

One factor that doesn't seem to matter much is minor differences in weight of the cement filled projectiles. Last fall I did some experimenting with groups of three cans that varied an ounce in weight.  Fired three series of three each, one of each weight in each group, numbered for clear ID.  There was no clear consistent  pattern in their distribution by weight.  All powder charges were weighed to the grain and the barrel swabbed between each shot.
One thing that did become obvious was a one over, one under, and one on the money pattern, not much lateral spread other than one "flier".  I don't know what if anything this means or if it applies to other projectile forms.
Anybody else try this?

[RocklockI]

Do you have any spare cans ? If not I'll be eating asparagus today .......I've got some ideas on this very subect ,as you know .

Mine will be slits in various places

'Delayed-Deployment, Shuttle-Cock Guidance Assembly'  KISS ?

Its sounds like something coming out of Ball Aerospace in Boulder

The old "DDSCGA" ? eh?  

I'll go for a minni ball type thingage and let the 'skirt' expand ,no flip around at at the muzzle for me .

I believe once it flips it will keep on flipping and flipping and stop !  

But like has been mentioned .......accuracy is .....is in the eye of the beholder ...whats it matter you need to hit minute of earth .  

By the way ,are the can sizes marked on the can ? what brand aspaergaus ? I have a need to know .

[seacoastartillery]

     Thanks for the quick response, gentlemen.  Tim, nice of you to volunteer to get us that list of "things that effect accuracy".  

     Boom J,   "Attaching fins to a soup can" is not so outlandish, and may actually work!  Maybe we will get to observe some flight results, real results, empirical results, as our intrepid inventors set out to challenge the old-world, established accuracy standard, the round ball.

     Victor3,    Very interesting, I see that we are progressing on parallel tracks.   As your idea seems to be simpler, it has a good chance of working better than mine, perhaps we will see evidence of both.  For a former 12 year old kid who made his first matchlock pistol from a piece of 2x4, a section of music stand and other scraps, you do get my garage-tinkering spirit kindled.

    Thanks to Gary for his M.B.F.F.P. idea.  The KISS Principle is clearly guiding his,  'Muzzle Blast Forged Fin Projectile',  design.  Basically, he said to me a couple days ago,  "Are you nuts, Tracy?  That idea is way too complex.  Just pour lead in the bottom and split the can in strips down to the lead.  Load fin side down."  I think that, because the lead plug will have lots of "Inertia-at-Rest", you will have a lead plug with a shorter, attached, 'Squashed steel fin Plug' emerging upon firing.  Maybe not. Anybody?  I would load it, Lead down, and let it be an A.F.F.P., an 'Air Forged Fin Projectile'.  It might have a good chance to be accurate, looking exactly like a "Shuttle-Cock".

There must be more ideas out there.  I'll post my sketch a bit later; maybe that will spark some other ideas or debate.

Tracy and Mike

PS   I see there are more postings.  Thanks, Gary and thank you, Little Seacoast.  Never have tried that, but sounds like you are ahead of us all with your observations.  I would think that weight would matter quite a bit as far as 'range' or 'distance of flight' goes.  Maybe not.

Gary,   We are using 'Green-Giant', 15 oz., double-rim, steel, Asparagus cans.  These are 2.656" O.D. x 2.560" I.D. x 5.600" long.

[dan610324]

a little heavier projo needs a little more speed to achive the same distance ,
but maybe the slightly heavier projo makes a little more resistance in the beginning before it starts moving so the pressure get a little higher and thereby gives it a little more speed

dont know , just a thought

[RocklockI]

Here is the newest thought , a finned projo . The fins extend on launching from gas blowing them open .

Straight and true . Now i must come up with an equaly simple nose cone .

Gary

eta I meant concrete not lead as shown .

[seacoastartillery]

    Dan,   I have always thought that to be true, but I don't have any proof.  I hate to think of the damage one of these 'Experimental' projectiles could do to Mike's Ballistic Chronograph, but it could be substantial.    Maybe a heavy steel deflector plate could be employed.

    Gary,   I had to study your sketch a bit, but now I understand how the little fins fold outward to their "Deployed Position" after being acted upon by the gas pressure produced upon firing.

Interesting ideas, these are.

Mike and Tracy


Gathering parts for the Shuttle-Cock, Vane Guided, Tin Can, Mortar Round.  The springs will be cut in half to make 12 pcs.  Aluminum plugs for turning the 'Vane Deployment Body', 2.75" dia. X 3.00" long, #2 tall can, tiny screw eyes to hold bottom end of the 'Vane Actuating Springs', and 1/16" wire-stem surveyor's flags to obtain the L-shaped wire attached to the Vanes that the 'Vane Retainer Ring' will hold onto until shortly after firing.  The thick washers simulate the 1/4" thick, steel, 'Vane Retainer Ring' which will be turned from 12L14 steel.  Not shown are the Baltic Birch spacer, lead weight, and 5/16" dia. Aluminum Vanes.




A prototype drawing showing most parts in 'section'.  Can you see how the "Inertia-At-Rest" of the 'Vane Retainer Ring' deploys the folded Vanes moments after clearing the Muzzle Blast?  There is a moments delay there as the can and all rigidly held components are propelled out of the mortar.  The Vane Retainer Ring holds all the stiff, steel, L-Shaped wires which are brazed to the aluminum vanes and hooked into the I.D. of the Vane Retainer Ring.  This ring slides down into a recess, releasing all 12 wires and the Shuttle-Cock Vanes attached to them.  The projectile does a graceful end swap and, Voila!  Accuracy is achieved, we hope.

[lance]

Fins and wings, here's a picture:

[RocklockI]

whoop whoop whoop whoot  splat . You might get a nice fragmentry splat with all the assorted bits and vanes flying around on impact   .

This s/b fun .
Gary

[Cat Whisperer]

...
 Tim, nice of you to volunteer to get us that list of "things that effect accuracy".  
...
Tracy and Mike
PS   ...

OK, glad to.  

Then when the experiments are done, comparisons can be made.

In order to have comparible data each experiment should report extreme spread of a given # of rounds, say 3.  Also such data as bore diameter, length, charge, etc. etc.

[Double D]

Why do I get a Jules Verne like feeling reading this thread!!!! 

[Cat Whisperer]

Because it's cannon related?

[lance]

I want to know what Mike and Tracy think about the wings, in the pic i posted on reply #10.

[dominick]

   Dan,   I have always thought that to be true, but I don't have any proof.  I hate to think of the damage one of these 'Experimental' projectiles could do to Mike's Ballistic Chronograph, but it could be substantial.    Maybe a heavy steel deflector plate could be employed.

    Gary,   I had to study your sketch a bit, but now I understand how the little fins fold outward to their "Deployed Position" after being acted upon by the gas pressure produced upon firing.

Interesting ideas, these are.

Mike and Tracy


Gathering parts for the Shuttle-Cock, Vane Guided, Tin Can, Mortar Round.  The springs will be cut in half to make 12 pcs.  Aluminum plugs for turning the 'Vane Deployment Body', 2.75" dia. X 3.00" long, #2 tall can, tiny screw eyes to hold bottom end of the 'Vane Actuating Springs', and 1/16" wire-stem surveyor's flags to obtain the L-shaped wire attached to the Vanes that the 'Vane Retainer Ring' will hold onto until shortly after firing.  The thick washers simulate the 1/4" thick, steel, 'Vane Retainer Ring' which will be turned from 12L14 steel.  Not shown are the Baltic Birch spacer, lead weight, and 5/16" dia. Aluminum Vanes.




A prototype drawing showing most parts in 'section'.  Can you see how the "Inertia-At-Rest" of the 'Vane Retainer Ring' deploys the folded Vanes moments after clearing the Muzzle Blast?  There is a moments delay there as the can and all rigidly held components are propelled out of the mortar.  The Vane Retainer Ring holds all the stiff, steel, L-Shaped wires which are brazed to the aluminum vanes and hooked into the I.D. of the Vane Retainer Ring.  This ring slides down into a recess, releasing all 12 wires and the Shuttle-Cock Vanes attached to them.  The projectile does a graceful end swap and, Voila!  Accuracy is achieved, we hope.

Mike and Tracy,

This should be a very interesting project.  The Abrams tank has a smooth bore gun that uses a fin guided projectile.  If you google Abrams tank projectile you will find one. Are you placing the vanes on an angle to impart a spin on it?  Feathered arrows have this feature, however model rockets do not.  Dom.

[Cat Whisperer]

Ooooo Oooooo Oooooo

ROCKET ASSISTED !

Well, maybe for another day....

But looking at your pictures, gives me an idea of turning different diameter projo's for comparison.

Not sure how to do varying lengths of barrel.

[Cat Whisperer]

Seriously, now, thinking through accuracy principles.

One would think (a way of saying that I do not yet have emperical evidence) that:

a) a closer fit to the bore would be more accurate than a looser fit.

b) that a longer bore (to a point) would be more accurate.  (the point being where the flex in the bore from the barrel being excessively long affects accuracy)

c) that the greater the mass of the cannon/mortar the better, as also the ratio of mass of the mortar/cannon to the projectile.

d) that the smoother the bore and more spherical or cylindrical the projectile, the better.

e) that the more aerodynamic or stable in flight the projectile the more accurate.

[seacoastartillery]

    

whoop whoop whoop whoot  splat . You might get a nice fragmentry splat with all the assorted bits and vanes flying around on impact   .

This s/b fun .
Gary

     Watch it buddy, although we couldn't hit you with this thing on a bet, Remember Always that you are within range of the Paixhans Monster Mortar and it's 137 pound, solid-concrete, prairie-penetrators!

     Good idea, Tim.  Double D,  we just don't know why.  High-tech expectations of low-tech equipment?  Maybe?

It IS cannon related!  No off topic stuff here!

    Lance, I forgot to scan all the postings with my radar turned on.  I love it and remember seeing it in a book on the War between the States Projectiles that I saw once at a gun-show in Tulsa, OK.  I really like the fact that it was designed to be fired from a high velocity gun, the 6-pdr.  Difficult for a garage mechanic to duplicate those shapes without special equipment, I believe.  Even making those fin-actuating,  v-springs would involve lots of work.  Certainly it's unique design would encourage experiment!  Any info on test firing results?

Must find 2 lbs. of lead, 'til tomorrow,

Mike and Tracy

PS, Thanks Tim, those sound very logical to us.

[RocklockI]

Well said Tracy . You are going to use lead ? I was thinking concrete ?? Either way I now think I will need a filler to fill the butt end of the can ?

One time you said something to the effect that grits would best be used as a case filler .IIRC .

I dont have any grits ,BUT I do have some cream of wheat .  I dont think a reasonable charge would launch a 1/2 hollow projo with any reasonable charge and extend the fins.

So instead of filling a case with filler ,I'm filling the projo with filler .    I've been thinking of fillers ,when I was a kid kapok is all the gun writers ever wrote about .......The only kapok I'd ever hear of was in those old life jackets .

'Some' experiments maybe in order ..............How about a flour filler   ? NOT you might leave a flaming rocket effect going out straight and true . with no woop woop . The possibilites are something to think about and approch with all due caution .

Tracy said something to me in 1981 when we worked together . We were chatting about things that go bang and the 'extreme' caution Tracy took with it all .

I asked about some seemingly over cautious method he did about things that go bang . He looked me in the eye and said " You know I want to be doing this when I'm 70 ,and I want all my fingers and eyes to work ."

I held Tracy in high esteem back then as he was so much older than me   then ...?

I vividly remember thinking '...damn that guy is very smart !'  Seriously This conversation took place in the mechanical recieving inspection room  ,he may not even remember as he was so much older than I .

Now he still both eyes and all 11 fingers , and so do I so it was good advise .

He sure was smart , back then , and I think he may have reached his foretold age about now ......Good advise ! Thanks Tracy

Gary

woop woop  

 

 

[seacoastartillery]

     Dominic,   Although we are not slanting the vanes to obtain a helical spin, we sure did closely study a tungsten rod penetrator designed for the 120mm smooth bore gun.  It is just amazing that accurate cannon tubes have come full circle all the way back to smooth bore after all these years of rifling development.  Looks like very accurate machining on this saboted, sub-caliber round.  The sabot petals must be very precise too, holding that penetrator in the exact center of the smooth bore tube.

     Tim I think that characteristics a, d and e might hold they key to increased accuracy, what say you?  Rocket Assisted?  Maybe for someone who lives in an area with less fire danger than we have.

     Gary,   You can try some basswood filler in there.  It's lightweight and more resistant to pressure and flames than Kapok, popcorn puffed oats or cream of wheat, and besides I'm developing a taste for grits.     Gary, you have almost caught up to my age, but about the wisdom and caution part, well, er, let's just say this: when I need some advice on how to draw, design, represent visually, or need an honest forthright second opinion on something, I will come to you.  About flower filler or Cremora, I wouldn't unless you want a flashy muzzle blast effect, a la Hollywood.  I'm glad I gave you good advice in '81, but remember this: I was much smarter back then.   

Regards,

Tracy and Mike

     

[Victor3]

Alright, now everything is as it should be in BPMC-land! Victor has returned... Welcome back buddy!

 And I'm here with a "can-do" attitude.

 Now then..... Let's have a look at M&T's design. Hmmmm.....

[Victor3]

 I was just looking at Space Exploration Technologies new nine engine rocket down at Cape Canaveral. Do you do design consulting for them on the side? 

 Looking at the sketch...

 Are you sure your weight distribution will allow the projectile to turn around and stabilize quickly enough?

 Maybe I'm not interpreting things correctly, but the surface area of your fins looks maybe like it should be increased some in order to be effective?

 Not to be a party pooper, but that design looks like it will require a lot of work to machine, assemble, etc. If you're thinking about a projectile that turns around in flight, wouldn't a simple, light weight 2' long 'dart tail' do the job?

[RocklockI]

Victor3 you asked

I was just looking at Space Exploration Technologies new nine engine rocket down at Cape Canaveral. Do you do design consulting for them on the side?  

 Looking at the sketch...

 Are you sure your weight distribution will allow the projectile to turn around and stabilize quickly enough?

Thats a good one Vic3  "Are you sure ...! " good sense of humor   LOL some guys can tellem and some guys can't .

"Are you sure....." Thats funny ...... "Oh YEA He's sure allright   " heehhee har Gaffa gaffa har har TEe Heee     ...good delivery too Vic3

Tracy you might consider leaving abit of the flags on each tip for more drag
"I am sure that would be enough drag " teeheee harrheeeee .

Thanks for the drawing compiments btw . are you sure this is keeping it simple ?
Sure ,compared to an Iodine Laser Cannon or landing a man on Mars ........

Your ol buddy Gary

[seacoastartillery]

 I was just looking at Space Exploration Technologies new nine engine rocket down at Cape Canaveral. Do you do design consulting for them on the side?       No, but I inspected lots of rocket and satellite parts and assemblies when I worked for Martin-Marietta and Rockwell in the 80s and 90s.

 Looking at the sketch...

 Are you sure your weight distribution will allow the projectile to turn around and stabilize quickly enough?     I'm fairly good at visualizing spatial concepts, so I'm pretty sure it will, but having not run any pitch, yaw, rotation and spin algorithms, I can't say for sure.

 Maybe I'm not interpreting things correctly, but the surface area of your fins looks maybe like it should be increased some in order to be effective?     On this point, I think you are entirely correct, but I prefer to build it and see what happens, rather than relegate this one to the trash can based on scienterific theory.  I want to observe this design's behavior with a normal and also a high speed camera to gather some empirical evidence of it's flight characteristics.


 Not to be a party pooper, but that design looks like it will require a lot of work to machine, assemble, etc. If you're thinking about a projectile that turns around in flight, wouldn't a simple, light weight 2' long 'dart tail' do the job?   Victor, you are an intelligent fellow and a logical thinker, so I seriously consider what your ideas convey to me.  But in this case, let's just try it and see what happens.  Maybe we will do 'dart tails' next, or perhaps we will try Gary's concrete and Creamora round.  

Regards,

Tracy and Mike

PS   Gary it is simple compared to an Iodine Laser Cannon, is it not?  Besides, Victor was serious when he asked and said those things, unlike your mockery.  After all, he knows a serious experimenter when he sees one.  By the way, I AM sure it will Flip and pretty darn sure it will not Flop!  

[benzon]

From a lurker,

My thought was to use common mouse trap springs to extend the fins.  Cheap and expendible, once the design was finalized. Would need a bit of brazing and all that.  Or perhaps a bit of JB Weld. Install the spring/fin assembly in the end of a cement-filled tin can somehow, stick it down the barrel backwards with the fins tucked in tight (carefully, to save your fingers), light the fuse and let it fly like a shuttlecock. 

My other thought was that fins that extended beyond the diameter of the round may not be necessary.  Older military mortar rounds fit the barrel without deployable fins.  Make an X out of 1/16 inch or so sheet aluminum, sink this into the cement-filled tin can as the cement is hardening, and there you go.  I think the fins would even survive if the round was loaded fin first.

I fire an old Sculler Lyle Gun sometimes, and a couple of golf ball mortars a lot.  Fins on a golf ball?  Hmmm.

Regards,

benzon

If all this is old news for you folks from previous threads, I apologize.

[lance]

Mike and Tracy, glad you love the picture, if i find any test info, i'll pass it along. I would think that if you added the feature of the Hale War Rocket to it, might make for a very interesting combo. I always enjoy watching these experiments, and can't wait to see how they turn out.

[Cat Whisperer]

...
I fire an old Sculler Lyle Gun sometimes, and a couple of golf ball mortars a lot.  Fins on a golf ball?  Hmmm.
...

Good to have you on the board Benzon!

We'd love to see some pictures (smoke and fire or others) of your toys!

[seacoastartillery]

     We second cat whisperer's welcome, Benzon.  Sounds like you have some interesting ideas, after all those 60mm and 81mm rounds I fired while in the US`Army Infantry, you would think that I could remember that those fins fit nicely INSIDE the bores of those two mortars!  You are certainly correct here: we will make a point of looking into this idea.  We bought our first mortar from the fellow who wrote the most complete book on The Life Saving Guns of David Lyle,  Mr. J.P. Barnett, the founder of South Bend Replicas, Inc. Thank you Benzon; your ideas are not old, they are new and pretty darn good ones we believe.  

    

Mike and Tracy, glad you love the picture, if i find any test info, i'll pass it along. I would think that if you added the feature of the Hale War Rocket to it, might make for a very interesting combo. I always enjoy watching these experiments, and can't wait to see how they turn out.

     Lance, that's a good one, you're referring to the helical nozzle design, I assume.  This could be done with copper tubing bent into a helix shape, maybe three of them and laid into a can which receives a dry mix of high strength concrete and then some water and set aside until cured and dry, then cut the can's bottom out.  A wood disk sabot would stop propulsion gases from going up the copper tubes, bypassing the can.  Remember to put sand into the copper pipe before bending it, as you want smooth bends and no kinks.  Thanks Lance!  What a great idea.

     I agree with Cat Whisperer, (Tim), we want to see smoke and fire from Benzon as he saves a canoe full of pretty girls with his Lyle Gun just before they go over the falls on the river!!  Now THAT would be a shoe-in for a winning Calendar Photo.  

Tracy and Mike