Possible golf-ball mortar design

[Meche_03]

I've been a troll here for several years, but just signed up as a member.

I'm looking to create a golf-ball mortar that should look nice and shiney while being functional. 





Its a bit modified from a "normal" mortar as I have modeled it so the trunion is completely surrounded by the chamber end of the barrel.  It is loosly based off of an EZ build listed on this forum.

Bore is 1.7" I.D. with a depth to powder chamber just under 2xID
powder chamber is .75" I.D. by .75" deep.
fuse hole is 1/8" diameter
trunion is .75" O.D. and 4.5" long.
Maximum O.D. of barrel is 3" with narrow bands at 2.75" I think, don't have cad at home.
bed has cavity contoured to match barrel set at 45 degrees.
Bed, right now is 2"x9"x5"

I will probably make the prototype out of 1018 or 1020 steel.  I would like to make the gift versions out of stainless steel or bronze so they polish up nice without worrying about rust.  Stainless steel is very easy to find as scrap around here so I'm leaning towards that but have not researched or desided if I like the material for a "cannon".  I know Marlin make a good many 45-70's with SS receivers and breaches so I know it's possible.  I will end up laser etching information on the muzzle of the barrel and if possible on the top of the barrel.

Any tips/comments on changing the design for the better would be nice.  I haven't figured out what length handles I want on it yet.  I'm pushing for 3" wide so they are functional.

[Double D]

I've been a troll here for several years, but just signed up as a member.

Ah perhaps you have been a lurker....we ban trolls.   We are are always glad to have lurkers come out of the closet

Its a bit modified from a "normal" mortar as I have modeled it so the trunion is completely surrounded by the chamber end of the barrel. 

Any reason  why? 

With design you have and the smallish trunnions they will be a bit long and may bend.  The way the trunnion attaches will require more detailed in letting to fit the barrel in the base.
 

[GGaskill]

This stainless steel mortar was originally bored 1" which made it look sort of like an 1841 style seacoast mortar, although the profile was more that of a Coehorn.  After the beginning of the golf ball craze, I rebored it to golf ball bore (1.72") so it is now much more like a Coehorn but the mount is wrong (I am keeping the mount as is) but life is like that sometimes.  It is all stainless including the custom hardware.  The wood is walnut for a pleasing contrast (when not observed under strobe lighting.)  An interesting attribute of the stainless is that it cleans a lot easier than my mild steel ones.

As long as you shoot only golf balls, your trunnion should be plenty strong, but should you start shooting the iron golf balls available from Fox Industries, I would wonder.

[Cat Whisperer]

Agree with George's last comment.  Surrounding the trunion gives it nice clean lines!  Cool, maybe not tratditional, but nice lines.

Build it for strength - down the road it may get used with steel or lead balls.  Make sure you hve enough metal below the chamber AND round the inside transitions of the powder chamber to reduce stress risers.

It's a GOOD feeling to see something that you've designed in CAD come to life in steel or bronze!

[Double D]

A base like George's would work better with the barrel extension you have.  Pleanty of clearance.  The triple arc the bottom of the barrel are going to make it labor intensive to inlet the base. Rounds are not that hard to inlet, three balls will call for some skill. 

That smaller bottom area does give it the lines of a British Grenade mortar which is a nice design, but this trunnion need to be at least one inch diameter.

 

[Terry C.]

1.7" is too small for a golfball with proper windage. My bore is 1.725" and is pretty close to ideal

Actually, if you superimpose the shape of the traditional Coehorn onto this one, there is no real difference in the supported length of the trunnion. The protuberance extends around and behind the trunnion, but from that point forward the butt is basically the same as the rounded one we're all familiar with.

I do agree about the diameter, .75" is too small.

I also feel that the powder chamber should be smaller in diameter and deeper (even if you have to decrease the bore depth slightly). That wide shallow chamber is going to give you headaches.

[Meche_03]

I understand where many think the trunion having a diameter of .75" is too small. 

If it was suspended like a seacoast mortar I would use 1.0" at a minimum.  As of now I am looking at completely supporting the trunion and breach of the mortor in a contoured negative space in the bed.  The bed contour will be difficult to make except I have a friend with a cnc 5 axis mill.  Even with a 3 axis mill I can cut the contour in two setups.  One set up with the bed flat and using a .5" ball endmill and a second setup with the bed at 45 degrees and a flat endmill.

I will change the bore out to 1.72-1.725" tomarrow.

I like the idea of changing the powder chamber too. What about a 0.5" diameter by 0.75" deep?  I haven't figured out my maximum volume of bp I would use yet.  If I did that then I could back calculate dimensions of the chamber needed.  Try to make it a bit idiot proof. 

My goal is to make a prototype for me and then have them made for Masters and Ph.D students graduating with an  Explosives Engineering degree.  Should decrease the number of idiots using them, but....... we all like to use the P for plunty method sometimes. 

I did a basic FEA on the design to caluculate Safety Factors using a powder chamber pressure of 1500psi and a bore pressure of 500psi.  Got those numbers off a graph on this forum ,I think.
A36 = SF of 11
316SS = SF of 7.5
4340 = SF of 21
304SS = SF of 9
1015 = SF of 14.5
Al-Bronze = SF of 12.5
90-10 Bronze = SF of 3

So it appears to be "safe" though the FEA does not take into account sharp impact loading.

[Terry C.]

I can tell you from personal experience that, tested with Fg powder, a 9/16" diameter x 3/4" deep chamber will hold 42.5 grains and a 5/8" diameter x 13/16" chamber will hold 60 grains.

These are hemispherical bottom chambers, not hard to do.

Given my choice, I would go with the 5/8" x 13/16" chamber.

What you don't want to do is overchamber your mortar. Been there, done that. I have a GB mortar that has a capacity of 240 grains. It's never been charged to anything close to capacity.

[Double D]

I like the idea of changing the powder chamber too. What about a 0.5" diameter by 0.75" deep?  I haven't figured out my maximum volume of bp I would use yet.

Why don't you do that first. Figure out what your performance you are looking for.  You could make simple basic mortar, do some shooting test and them fine tune you elaborate design from those test.
 

I did a basic FEA on the design to caluculate Safety Factors using a powder chamber pressure of 1500psi and a bore pressure of 500psi.  Got those numbers off a graph on this forum ,I think.
A36 = SF of 11
316SS = SF of 7.5
4340 = SF of 21
304SS = SF of 9
1015 = SF of 14.5
Al-Bronze = SF of 12.5
90-10 Bronze = SF of 3

So it appears to be "safe" though the FEA does not take into account sharp impact loading.

What is a FEA and where did you get these number?

[Cat Whisperer]

FEA is Finite Element Analysis - which lays out a matrix throughout the 3d object and calculates stress/strain.

I'd like to see what it does around the transitions  - rounding vs sharp corners inside the powder chamber.

It's genuinely good to see someone else recongnize the effects of impact loading.     That's were mild steel revolutionized the cannon making industry (and others) in the late 1800's.

[Double D]

Haven't heard the term since college...but then in my two professions I haven't had a need for that type analysis.

[Meche_03]

got the pressure data from .http://www.gboreloaded.com/forums/index.php/topic,211975.0.html and bumped the numbers up just a bit.

[Double D]

To replicate thoses pressures you need make a powder chamber equivalant in shape and size to the chamber that generated those pressure plus you will also need the same windage.

[Meche_03]

yes the specs would have to be the same to get results close to those shown.   The "windage" was 0.040" and all charges were 120 grains.   The highest pressure was with ffg.  To be conservative I used the ffg curve and bumped it up just a bit due to the windage on my design being just abit lower.  If I went with the 60 grains powder chamber suggested then the FEA would be really conservative.

[Double D]

The only other suggestions I have are for aesthetics.   This design just begs to be in bronze.  The transition from barrel to reinforcing band should be a radius.  An lastly the trunnion needs to be larger. The smaller trunnion looks spindly and cannons and mortar look  should look massive.

What wood are you using for the base.  If you are going to make this a show piece you need something fancy.

[Meche_03]

I am aiming for it to be made of a bronze of some sort.  I'm thinking stainless for Masters degrees and bronze for Ph.Ds.  It doesn't show up well but I have radiused the reinforcing bands at all intersections with the main barrel.  Well if for no other reason than to look right, I could change the trunnion to 1".   If the trunnion becomes 1" I might make the sled a bit thicker too.  I don't want just 1" of wood under the trunnion. 

The wood is up in the air still.  The University is in Missouri and Oak is all over the place there.  The scrap wood from the barrel stave saw mills is really good wood.  I think I would want a darker wood with the bronze and a lighter wood for the SS versions.  Maybe same wood, just different stains.  Walnut won't look right to me though a good cherry grain might look good under the bronze.  A honey colored Oak for the SS might be good.

I was thinking about putting two matching pressed in pen holders on the 45 degree cut on the back side of the set up.  Make it a desk piece but the holder could also hold loading and wash equipment out in the field.

[Double D]

To get a ratio....The trunnion on the 24 PDR coehorn is 2.5 inches and the base is 9 inches thick.

On the pen holders pit them on sockets so the can be removed for shooting.

Something I just noticed on the 24 PDR, it has a 1/4 round moulding instead of an angle on each end of the base.  The moulding has a 3 inch radius and is recessed 1 inch from top and front. 

[GGaskill]

There seem to be three styles of end treatment on the wartime Coehorns.  The fancy one with the recessed arc, a plain arc without recessing and plain 45° chamfers.  I can't find the traditional picture showing all three.

[Double D]

I know which picture you mean George.  I beleive it is a picture of captured Confederate weapon at Richmond. 

[GGaskill]

Yeah, that's the one.  I don't know if those were entirely Confederate manufacture or captured Union guns; my feeling is originally Union due to the more ornate design, but a lot of Federal ordnance was in southern locations at the beginning of the WfSI (War for Southern Independence) because the head of the War Department anticipated the event and a lot was captured in battle.

[Cannoneer]

Keep in mind that the mortar bed on the right (with the rounded shoulders) in the period photo may be a unique design, because (as far as I know) there's no other record of that type being used, while the two other bed designs seen in the picture are well documented.

[Double D]

The one on the left is the one that appears in the official plans...the others were probably product of war time expediency.  The south took it one step further--squared block and straight tube.

[dan610324]

was they also made from cast bronze , or was it iron ??
do you got any drawings with dimensions ??

[carronader]

for me , only one wood for a bronze barrel...mahogany. Has the barrel got to be referenced to a specific design ( coehorn ) yawn. a big world out there...if you go with an american ...even Brit...you are limiting the sled to virtually a slab of wood. If you are open to Euro design I can email you some designs. you would have a hybrid unless you could persuade the Colorado rodent to make barrels for you. ( Rocklock )

[Max Caliber]

Here is a drawing from the Cival War showing the ends of the bed beveled.



Here is really a great drawing from the Cival War, "Coehorns - Cold Harbor". Note that all three Coehorns are shown with beveled ends and sides. That would not be possible with the standard width bed but, who knows, could be that some wider beds were made like that. Probably just the artist adding his touch though.

[Double D]

Carronader post away!!!

[carronader]

didn't say post

[Double D]

didn't say post

I know you said email.

[gulfcoastblackpowder]

I agree with the correction.  Please post the pictures.  We all want to see them!

[carronader]

no interest from originator............going back in my box. Not many show interest in older Euro stuff , and of course involves a lot more work.........from beginning you gotta make your own drawings , I came on here looking for plans , got hooked , and now get enough info from vague old drawings to make my own. If a dumb Scotsman with no machining skills , no draughting education , can do it.....any of the lurkers out there surely can. Internet is full of old interesting stuff........you just gotta take the time and mostly the patience to go looking. Hell , you can even find action shots. 
 you could build that sled.........