How 'bout some ideas for making approx. 9.5-inch mortar balls?

[cannonmn]

I posted some pix in an earlier post showing the mortar we're restoring to shooting condition.  It should be done in a month or so, and of course we'll want to shoot it the next day.  The actual bore of the mortar is 9 9/16 inches, so we'll want a ball that's just a bit less than that, and we can work out the exact diameter as we go.

I'd greatly appreciate any ideas on how to make a ball to shoot out of it.  The ball can't be solid zinc as it would be too heavy, so it has to be a lighter material, or cored, or heavy core/lighter exterior.  We'll never need to fill it with anything so it doesn't need to be hollow like originals, unless that just happens to be the result of the design we adopt.

Looking at the weights of similar-size original mortar shells, I think I should be looking for something in the 70-80 pound weight range.  In my  limited experience with mortar shooting, I didn't get very consistent accuracy with lightweight mortar balls.

Here a are a couple of things we thought of, and there were some ideas in comments to the other post.

1.  Steel mold for zinc alloy casting, calibrated for zinc shrinkage, or for kirksite, two sides, with provision for core insert (this will be way too expensive to have made I think.)  If anyone can make one of these, complete with alignment pins for around $500. or so, please contact me, but I think that may be way too optimistic.

2.  Take standard 9.5 in. inflatable basketball, immerse in water or whatever, then fill it with wet cement and hope it stays round until it hardens.  Shoot it with basketball still on to protect bronze bore from concrete.   A variation on this idea is to make a two-piece "mold" out of plaster or concrete, using an inflated basketball as a pattern.  This would be clamped around the cement-filled basketball while the contents harden, to ensure it stays round.

3.  (from other discussion) Take heavy core and wrap with fiberglass and epoxy until it is proper diameter.  This will be really messy and probably takes more patience than I have in my whole body.

4.  Shoot easier-to-make cylinders made with prefab cardboard tubes and concrete, or something.

5.  Shoot 8" ball since people have molds for that size, and use plywood sabot to fit it to the larger mortar.

6.  _________

7.______________

8. ______

[cannonmn]

It looks like a 9.2-inch solid concrete ball only weighs about 34 pounds,* but that would be a start if I could make one of them-maybe figure out how to add weight to it symmetrically later using lead or something.


*assumed density of concrete is 145 lb/cu. ft., volume of 9.2 inch diameter sphere is 0.236 cu. ft.

[SHOOTALL]

you might be able to use old EMPTY refigerent drums , they come in different sizes , the 30 lb. size looks about 9.5 but thats eyeing it .

[Double D]

First, up in the reference section at the top of the board we have a link To GGasklills Spherical Shot Weight Calculator

We may have a source for you to have a steel round ball mould made.  I will send you a PM.  This might be the one that would be best served by a cast aluminum ball. 

If it were my Mortar I would call Paulsen Bros and ask them where you might get shot.  The other person to contact is the guy out at Back Creek Gun Shop.  He was having sombody there in Northern  VA cast his 24 PDR's.

I definitely would not shoot a uncoated concrete ball out of a bronze mortar.  You will abrade the bore. 

Looking at the 8 inch and 10 inch mortar they had windage of  1/66 and 1/76 respectivly.  So for your 9.5625  inch bore you would want some thing around  9.418 to 9.437.  9.5 might be a bit tight and push pressures in an old bronze gun.   


Spherical Shot Weight Calculator

Shot Diameter (inches):   9.418     
   
 
Lead (710 lbs/ft3): 179.71705415361825 lbs.                  Pb-10,Sn-1 (*685 lbs/ft3):  173.388988866519    lbs.
Zinc (ZA-3) (418 lbs/ft3): 105.8052516002992 lbs.         Wheel weights (*684 lbs/ft3): 173.13586625503504     lbs.
Aluminum (169 lbs/ft3):  42.66634739173787      lbs.         Pb-20,Sn-1 (*696 lbs/ft3): 176.17333759284267     lbs.
Cast Iron (437 lbs/ft3):  110.61458121849462       lbs.         Lyman No. 2 (*685 lbs/ft3):  173.388988866519    lbs.
Concrete (142 lbs/ft3):  35.94341083072365       lbs.     
 

Shot Diameter (inches):   9.437     
     
 
Lead (710 lbs/ft3): 180.8069407653826 lbs.            Pb-10,Sn-1 (*685 lbs/ft3): 174.44049918913674     lbs.
Zinc (ZA-3) (418 lbs/ft3):106.44690315483088  lbs. Wheel weights (*684 lbs/ft3): 174.1858415260869     lbs.
Aluminum (169 lbs/ft3): 42.92509568368013 lbs.     Pb-20,Sn-1 (*696 lbs/ft3):  177.2417334826849    lbs.
Cast Iron (437 lbs/ft3):  111.28539875277774 lbs.   Lyman No. 2 (*685 lbs/ft3):  174.44049918913674    lbs.
Concrete (142 lbs/ft3): 36.16138815307652  lbs.

Boy, George sure put a lot of decimal in those formulas

[Double D]

You also might want to take a look at our sponsor list at th top of the board for some one to make a mold for you.  Kap Pullen is just across the river from you in Maryland. 

[intoodeep]

cannonmn,

 If you are willing to go with the sabot routine. Then you could use the good ole' bowling balls..... They are much lighter than some of the other options. Hey, it's something to think about....




 

[Will Bison]

I like intoodeep's idea of a bowling ball with perhaps a discarding sabot to keep the ball centered and seal the bore. In the 70-80 pound range an alloy of Zn-Al would seem doable.

[Terry C.]

The other day Dom mentioned buiding a popcan mortar with a slip-fit sleeve to reduce the bore to golfball size.

Would something like that work here?

A removable steel sleeve that reduces the bore to bowling ball size would probably be a lot easier (and cheaper) to machine than a humongus ball mold. Money left over in the budget could be used to lay in a supply of used bowling balls.

What say, mortar fab experts? Would this work? Would it be safe? Why didn't I buy all that 9⅝ OD x 8⅝ ID seamless steel tubing that the company I worked for scrapped years ago.

Okay, so you can't answer that last question. The only thing I can say is for myself is "If I only knew then what I know now..."

[cannonmn]

For the sleeve idea I wonder how thick the sleeve has to be, and what kind of steel, to make sure it doesn't expand and become an unwanted, permanent part of the weapon?   

[lance]

Cannonmn, you'll probably laugh, but what about lathe turning some wood balls? i don't know what a wood ball 9.5" weighs, but if you are just shooting a 100yds or so they might hold up pretty well. wood can be tough stuff.

[GGaskill]

Boy, George sure put a lot of decimal in those formulas.

Javascript computes them like that.  My webpage only shows four decimal positions.   

Bowling balls will launch from an 8 5/8" bore, so subtracting that from 9 9/16" and dividing by two gives a wall thickness of 15/32" which I think would probably be thick enough to not become a permanent part of your bronze mortar if you don't try for maximum range.  But somehow you need to attach the sleeve to the bronze tube so it doesn't exit with the bowling ball.  Maybe a 1" wide band of epoxy at the bottom to prevent gas from getting between the layers and a layer of grease around the upper part of the sleeve to maintain the clearance.  You would have to heat the tubes to the failure point of the epoxy to get it out.

[cannonmn]

I think if I get a sleeve built for it, the bore will be just under 8" so I can fire 8" zinc mortar shells, since they are available.  The bowling ball idea is a good one but I'd like the ball weight to be close to that of original mortar shells for the bore size.

[Artilleryman]

If you use DD's table a solid aluminum ball weighs 42.6 to 42.9 lbs which is almost the same as an eight inch mortar shell (45 lbs, hollow).  So if you have the mold and a furnance and crucible that can cast that much aluminum it would probably work reasonalbly well at ranges under 500 yards.  At longer ranges it would probably drift too much if there was any wind.

[Double D]

If you line just the projectile bore you are going to have to have some means to achor the liner in place.  The other thing that may have to be done is the original bore may need machined  to allow the liner to fit.  The bore may not be round.

Even if you built a liner that included powder chamber it will have to be secured.

Sabot is the cheapest method.  I still think a phone call to Paulsens will turn up projectiles.

At one time I talked to an Aluminum foundry in Leesburg about casting me 6 PDR balls.  The Idea then was for me to leave the mould with them and at the end of the day they would "empty the pot" into my mould.  After a couple of weeks I would come and pick my round balls up.  Never did do it because I got my hands on a bunch of zinc and made zinc balls even cheaper.

   

[Double D]

If you use DD's table...

Norm,  just to keep the credit where credit is due...It GGaskill that we have to thank for the table...Thanks George.

[GGaskill]

My pleasure.  Let me know if there are any other computational type things you would like (you may have to supply the equations.)


At longer ranges it would probably drift too much if there was any wind.

If the aluminum shot is the same weight and same diameter as the original hollow cast iron one, I would expect the wind would affect them the same.

[cannonmn]

Thanks again for suggestions, lots of good ideas, keep 'em coming, there are NO bad ideas in this case. 

The liner idea is fading a bit, we don't want to modify the original tube at all. 

I will call Paulson and ask if they have any 9.4-inch balls or whatever lying around, they may have some suggestions.. 

It seems like we always try the easiest options first to see what works.  we shoot an original bronze gun that has an approx.  2.5 inch bore, and we get great results with concrete-filled tennis balls.  We get the balls free, used but not even dirty yet, from a local tennis club.  Maybe that's what made the concrete-filled basketball seem like a good idea.  As I recall we used anchoring cement, which has a very smooth consistency if you pour it quick enough.

The aluminum ball sounds good too, I guess if I make up a split pattern, a foundry could just sand-cast them?

Anyone else with a composite ball idea?  Even crackpot ones, like take a smaller aluminum ball that's available, anchor the end of a mile of baling wire onto it, and mount it on an industrial-sized string-ball winder, then dip the finished wire-wrapped ball into hot solder, then coat it with, with .... (maybe I oughta take a break)

Or re-designate the thing as a stone mortar and shoot baskets of stones, like the 16-inch and 17-inch "official" stone mortars I've seen at the military and naval academies respectively.  There's a cheap projectile, get some smooth river stones and some kind of basket that'd protect the bore, and that plywood sabot.  I'll at least have to try that.  Does anyone know what size stones were used in stone mortars?  They'd have to be big enough to cause injury to people on descent.

[Victor3]

Paper mache around a heavy core?

If I had something like that I'd look for chunks of aluminum round stock to shoot as is. If I felt I had to have round balls of exact weight I would machine aluminum ones from stock with a pocket to accept a lead slug. Might not be the cheapest way to go initially, but I would think they'd be fairly reusable(?) compared to most other options.

[cannonmn]

>Paper mache around a heavy core?

That's a possibility.  We did something close to that many years ago.  We were shooting a Turkish bronze Coehorn mortar, think the bore was about 5".  We had some 4" ? duckpin bowling balls we wanted to use, so we ripped up an old thin bedspread into long strips about 2" wide, then wrapped the strips around the balls tightly until they were a snug fit in the bore.  That worked fine.  I guess we could do that again using 8" balls this time.

[Artilleryman]

My pleasure.  Let me know if there are any other computational type things you would like (you may have to supply the equations.)


At longer ranges it would probably drift too much if there was any wind.

If the aluminum shot is the same weight and same diameter as the original hollow cast iron one, I would expect the wind would affect them the same.

That's the rub, the 9.5 inch alum. round weighs 42.9 lbs and the 8 inch iron/zinc hollow projectile weighs 45 lbs.   The 9.5 inch will have considerably more surface area than the 8 inch that can be affected by the wind.  The much heavier weight (70+lbs) of the iron hollow 9.5 inch will have better accuracy at longer ranges than the 8 inch.  So when you cut the weight of the 9.5 by using alum. don't expect the same type of accuracy that you would get with a full weight shell.

[cannonmn]

Here's an old official drawing of the mortar tube, on the upper right of this page.  Someone had asked about the chamber so this shows a profile of it.  I can post a blow-up of the drawing later if anyone wants one and can't zoom in on it themselves.

[Cat Whisperer]

I had a local patern maker make a mould for my 4.5" mortar.

I asked for a metal mould, he made a match-plate for sand casting.

The balls cast by folks here from zinc in metal moulds appear to be very good; those made from the sand casting do not stay round when cast.
The reason is that the sprue and riser come in from the sides - and tend to cool and solidify first, where the metal moulds are filled from the top and the sprue is sucked down in as the metal hardens.

A sand core piece is light, compared to zinc.  They're generally suspended by the ends - leaving a hole for filling the cavity.

If you wanted a hollow zinc ball conisder using a steel mould filled from the top with a sand core.  Perhaps out of the mainstream but potentially the best of both worlds.

[Terry C.]

I have seen molds advertised that cast a hollow lead half-shell. A hollow ball is made by gluing (?) two halves together.

Could a large mold, suitable for casting zinc, be made this way? I've personally never done it (yet), but I've seen cast zinc parts that were TIG welded together. If the walls were thick enough, they could possibly even be bolted together.

[accuratemike]

Get someone to make you a couple of spun aluminum hemispheres. (King Architectural has 8" & 12") Use them to cast concrete balls. Increase the density of the concrete by using metal aggregate (any steel scrap will do).... Just a thought. MIKE

Kings's balls: http://www.kingmetals.com/Default.aspx?page=category%20search%20results&CatList=0&Parent=907&tree=907*Balls*0@@

[cannonmn]

Thanks again for the suggestions, still working the issue.  We have one machinist with a radius cutter who may be able to machine two mold halves out of steel.  We'd make either cored zinc balls or maybe take it to an aluminum foundry and see if they could cast us some solid aluminum balls.  Also, we emailed the King Ball co. to see if they could help.  I'm going to NSSA Fort Shenandoah today to ask around, mortars are a big thing there now and the mortar match is this Fri PM.  I might pick up some 8" balls there so we could shoot them with sabots,

[Double D]

Going to FT. Shenadoah is a good move.  Those boy out there I am willing to bet will come oup with some good ideas and maybe even a solution.

Be sure and stop at Back Creek Gun Shop and stock up on supplies.

[cannonmn]

I went and talked to many folks about this.  One guy has two unknown 9" cast iron balls he'll bring tomorrow, since he's local, to see if I can use 'em.  If they aren't way to heavy, I'll take them.  That diameter is close enough that I could build up the remaining 1/4 inch thickness I need with, well, duct tape if it comes to that.

Also stopped by the shop you mentioned and will update my "military powder" discussion with that info.

[lance]

Cannonmn, i couldn't get off work friday, so i'll miss the NSSA mortar match.......... recon you could be a pal and put some pics on the board? please, pretty please

[cannonmn]

OK Lance, have some raw video, will take a while to turn it into one of our typical works of art, maybe by tomorrow.

Meanwhile here are the two iron or steel balls I got from my friend.  They are 9.09 inches in diameter and weigh about 92 lbs. each.  There are four dimples spaced around the equator of each.  The only thing I can think they may be is core rods, that supported a light core in the middle of the thing, so it would either not be so heavy or would not consume more metal than needed for whatever purpose it served.

Anyway I was tickled to death to get these perfectly smooth iron balls that pretty near fit the mortar I need to feed.  I'll use a few sheets of greased sail canvas large enough to surround the ball and come up the bore a little, to get a better fit, then put fire in the hole.  The canvas shouldn't go too far and some of it may be re-usable.  Since I only have two of these things I'll have to get a really reliable location method on the range.  I'll keep pursuing the molds and other ideas, as 92 lbs is just a bit heavier than I wanted.  I'll use a somewhat reduced charge due to the heavy shot. I'll get some ideas on powder charges by looking at the US CW era range tables for 8 and 10 inch seige mortars, and will begin at or less than the low end of the 8" tables.  I'll also figure the safe charge based on chamber diameter and see how that compares before I start.

[lance]

 GOOD DEAL CANNONMN!!! looking forward to the pics. i wanted to go, but with work and trying to get hay up for the horses this winter. well, i just couldn't spend the 4 hours each way on the road. Also looking forward to when you shoot those 92lb balls ya picked up, that will be a video all by it's self