GB mortar question(s)

[theoldsarge]

Hi guys.  Longtime lurker that just introduced myself.  Most of my time is on homegunsmith.com where I'm working on a almost scratch built .22 rifle.  Needed more golf balls for file handles (great if you've never tried them), so wound up getting 313 of 'em off of evelBay.  No way I'm going to use all those on files, so decided the no-brainer solution was a golf ball mortar. 

Now I've been doing my homework, google searches, searches here, searches on other forums, for days now, and still can't come up with all the answers.  I've got most of it all figured out, but not all.

OK, found some steel tubing, 1/4" wall, with 1 3/4" inside diamater.  Great, found some 1 3/4" steel rod for the plug too.  Wrong.  Found out it was not seamless.  Bummer.  Searching again, seems the only seamless I can find has an inside diameter of 1 7/8".  Too large?  I don't know, because I found a reference to someone shooting a golf ball cannon with a 1 7/8" bore with great results.  But I want a mortar. 

I figure a powder pocket of about 1/2" X 1/2" and a interior barrel length of maybe 2-3" or so.  So I'm wondering how this would work using seamless tubing with a 1 7/8: inside diameter?    I figure the steel tubing route will let me make one considerable faster than boring out a piece of solid stock.   What is the maximum inside diameter I can get away with using?  I will be shooting this at a range of about 16-30 yards at the most; well possibliy longer, but that's the promary distance I am interested in, and am aware that I may have to reduce the charge to keep balls within that range.

     Thanks for any input.

[dan610324]

make the powder chamber conical
1/2" at the top
2 1/2" deep
1/4" full radious at the bottom

[theoldsarge]

make the powder chamber conical
1/2" at the top
2 1/2" deep
1/4" full radious at the bottom

Isn't that a bit large for a little golf ball mortar?  I've not seen 'any' references to that large.  I only care about a range of maybe 200 feet maximum, not the next county.  If it's not too large, please explain to me why it isn't.  Thanks.

[Double D]

First, do you have a lathe or access to a lathe. 

From what you are describing it sounds like you might be making a K.I.S.S. pattern golf ball mortar.  If so you can use the welded seam material.

Here is a link to the post on my K.I.S.S. mortar. http://www.gboreloaded.com/forums/index.php?topic=70859.0

 All your questions will be answered in that post...

[theoldsarge]

First, do you have a lathe or access to a lathe. 
From what you are describing it sounds like you might be making a K.I.S.S. pattern golf ball mortar.  If so you can use the welded seam material.
Here is a link to the post on my K.I.S.S. mortar. http://www.gboreloaded.com/forums/index.php?topic=70859.0
 All your questions will be answered in that post...

Yep, got a lathe.  Already have the link to your K.I.S.S. mortar saved, great design.  But nope, not all my questions were answered there.

Learned some things today.  First, I had previously been given wrong information; I had been informed that DOM tubing was seamless.  I already knew that DOM meant drawn over mandrel, but what I did not know that it is actually metal formed into a tube, then the seam welded, and the result drawn over a mandrel to smooth the weld.  Interesting.  Especially as every thing I had been reading said to only make a mortar out of seamless, or bore one out of a solid bar, and to stay far away from welded tubing.  Apparently the writers of that bit of information were/are not aware that tubing is made from a flat sheet formed into tubing then electronically welded, but NOT drawn over a mandre.  The references/instructions I was reading were implying that DOM was seamless.  Interesting. 

OK, actually what one K.I.S.S. mortar page did not answer for me is the depth of the actual powder chamber.  I know it says to drill it 1/2" by 1 1/2" deep, but then you chamfer the top.  It looks like the chamber itself is about 3/4" deep, which  sounds aqbout reight, going by other build threads.

The other question it did not answer is, what is the maxim inside diamater of a golf ball mortar barrel that will work.  I figure I aill be going will be going with 1 3/4" but  am curious.

[GGaskill]

Golf balls are supposed to be 1.68" in diameter.  Different people use different amounts of windage (bore diameter in excess of projectile diameter.)  I drill mine at 1 23/32" (1.719") because it is a standard drill size.  1/40 windage (the forum recommendation) would be 1.723".  Your call since it is your build.

Experience has shown that a small diameter but deep chamber works best because it will fire a small charge as well as a big charge which is not true in large diameter chambers.  If you find the golf ball mortar contest thread, you will see that we built those mortars from tubing but when I build a golf ball mortar from scratch, I start with solid stock.  You have to remove more material but you don't have to mess with insert breeches or other complications like that.  It's all one piece. 

If you decide to get some Fox balls (steel golf balls), I would build one styled after a seacoast mortar instead of a Coehorn.  It would be a little heavier but greater safety factor.


(Robinson's Battery.org)

[theoldsarge]

GGaskill
From my research tho apparently golf balls vary in diameter at times, so I figured just going with 1.750 would cover all bases.  Like I said, it's just going to be a short range toy, so distance is not going to be a issue - if I have the opportunity later to be able to shoot at extended distances, I'll just make one with a bit smaller bore.     This first one or two will be just for fun, but I really like the looks of that seacoast morter a lot better than the Coehorn.  I'll be sticking to golf balls for all of my mortars tho, because I doubt I'll be able to find a place for longer distance.  Plus for long distance I like rifles.

Ah ha.  A powder chamber like that makes perfect sense, now.  Nothing I had read explained like you just did, in fact a few suggested no powder chamber at all, but that didn't really make sense to me - your explanation does.  Thanks.

I'm still wondering about how effective a 1 7/8" bore would be in a mortar without patching.  I don't plan on patching anyway, and will be building at 1 3/4", but still curious.  The thread I read on the 1 7/8" bore cannon claimed it fired a golf ball further than his 1 3/4" bore cannon.  That much windage it just doesn't sound really reasonable, which is why I ask, maybe one of  you gus has personal experience and can answer.  Thanks much for the help. 

Just remembered this, wish I could remember where I read it too.
While I was doing my homework I read about someone who claimed they had made a golf ball mortar using exhaust tubing for the barrel.  I would suppose that using a properly made breech plug, with a proper powder chamber, that exhaust tubing would be safe enough for one.  But I don't think I would care for the looks of one, even it it is safe.

[dan610324]

of course its possible to make an mortar from a piece of exhaust pipe
every now and then ther are some idiots showing their builds here who dont want to listen when we tell them that its pipe bombs they built and not cannons .

so can you do it ??  YES

are they safe ??  NOOOOOOO

do you want to kill or hurt yourself or your children ??
if so then there are easier ways .

for a golfball mortar with a small powderchamber designed to fire just golf balls I wouldnt make the low pressure part of the barrel any thinner than 1/4" at the thinnest point .

for a fox ball mortar I would say minimum 3/8"

of course a 1 7/8" bore will spit out the ball , but how far ?? have no idea on that , but sure not as long as a 1 3/4" bore .

[Double D]

 

First for the  K.I.S.S. design you can use welded seam tubing,

 

OK, actually what one K.I.S.S. mortar page did not answer for me is the depth of the actual powder chamber.  I know it says to drill it 1/2" by 1 1/2" deep, but then you chamfer the top.  It looks like the chamber itself is about 3/4" deep, which  sounds aqbout reight, going by other build threads.

First face off the plug and drill a hole 1 1/2 inches deep.  Then with your compound set at 30 degrees,    turn the cone section.  The powder chamber depth of the hole will be right.   Its not critical or important.  The only thing that is important is that the bottom of the hole is a thickness the same as or greater that the diameter of the powder chamber. I my dessign the the thickness is 1 inch.



 

The other question it did not answer is, what is the maxim inside diameter of a golf ball mortar barrel that will work.  I figure I aill be going will be going with 1 3/4" but  am curious.

Bit confused by this, do you mean O.D. of barrel or I.D. of bore.  The O.D. can be as big as you want.  The I.D. should not be les than 1.7.  If you are thinking using stock that is already 1 3/4 inch so you don't have to machine it, don't.  You will need to machine the bore to make it concentric. 

[Double D]

 

I'm still wondering about how effective a 1 7/8" bore would be in a mortar without patching.  I don't plan on patching anyway, and will be building at 1 3/4", but still curious.  The thread I read on the 1 7/8" bore cannon claimed it fired a golf ball further than his 1 3/4" bore cannon.  That much windage it just doesn't sound really reasonable, which is why I ask, maybe one of  you gus has personal experience and can answer.  Thanks much for the help. 

Just remembered this, wish I could remember where I read it too.
While I was doing my homework I read about someone who claimed they had made a golf ball mortar using exhaust tubing for the barrel.  I would suppose that using a properly made breech plug, with a proper powder chamber, that exhaust tubing would be safe enough for one.  But I don't think I would care for the looks of one, even it it is safe.

The standard for a golf ball is 1.68 inches.  No sense of going to the work and not doing it right the first time.  If you are going to use  tubing with 1.750 inch I.D.  you are going to have to machine it to make it concentric so it is going to be even larger yet. The larger the windage the more powder gasses can escape.  The closer you are to proper wind-age the more satisfied you will be with the performance of you mortar. 

Yes you could use muffler tubing, but the mortar will look amateurish and be far to light.  The muffler tubing would be marginally strong enough....maybe.

 If you are going to build, build it right and make it something you can be proud of.  These K.I.S.S. mortars tubing is thin enough. 

The K.I.S.S.  is a simple build and does not look bad when finished.


 

The only change I would make to the design is to make the base less tall.

[MikeR C]

Sarge,
You might consider looking here:

http://www.gboreloaded.com/forums/index.php/topic,85639.msg1099056401.html#msg1099056401

Starting about post #43 there is a discussion of Golfball mortar dimensions. My mortar has a chamber very similar to DDs and the problem I have is getting it to shoot short distances. A full load of FFFG gives me aprox 400 yds and is no fun as I can't see the ball, at all, not in flight or landing. At the Montana cannon shoot I had a heck of a time keeping the ball at thirty yards, I ended up using about 1 1/2 to 2 .22 shells of FFFFG but didn't have much consistency at that range.
It wouldn't suprise me to find that 1 7/8 bore would make it easier to shoot short ranges and the powder "wasted" would just contribute to more smoke and fire. (A good thing in my opinion ).
I don't know what kind of range and charge DD uses but it would be interesting to know.

Thx
MikeR C

[theoldsarge]

Boy, I'll tell you, I've gotten more useful info out of the replies in this thread than I have in all my days, well actually a few weeks, of searches. 
I'd already decided on a minimum of 1/4" walls, besides being sure that is safe, it looks better than thin, and if I can get the material I would prefer walls of 1/2", or more - for looks more than the safety factor. 
I'll definitely use a powder chamber, deeper than width. 
I'll be trying to get cannon powder, if I can. 
If I can get the material I'll try one with a 1 7/8" bore, so see for myself how it does.  If it uses extra powder to get a ball out 30-40 yards, no prob, it'll just mean more smoke, and more fun.
Didn't know I should machine 1 3/4" material to get the bore concentric.  Nice to know, so many people writing about their builds or whatever seem to assume people already know things like that.  Well, I didn't.  But now I do. 
My first build, and maybe any after that, will resemble the K.I.S.S.  mortar.  Not only do I like the looks, a lot, the build concept is approaching genius status.  Love the idea of taking it down to clean it.
Knowing I can use the welded tubing will cut the build costs considerably also, and may be able to find materials in my area low cost or even free.
Definitely will steer clear of exhaust tubing.

I really appreciate the responses on this, guys, I've been shooting and around guns just about all my life, plus 20+ years in the Army, I've read about weapons most of my life, and all of this stuff is new to me.  But now I'm confident I'll do a safe build.  Got a few other priorities before that, but I'll be posting photos when I do.  Thanks again all.

[GGaskill]

I'll be trying to get cannon powder, if I can.

While cannon grade is appropriate for certain larger bore pieces, I would not recommend it in a golf ball mortar when firing golf balls because of their slight weight.  I personally use FFFg when firing golf balls so the powder burns before the ball has left the barrel.

Here is a dimensioned drawing for golf balls of the 10" seacoast mortar of 1844.



You might make the chamber smaller than the one shown here.

Just for further information, in case someone wishes to build a larger scale version of this mortar, the full scale mortar is 27.5" in diameter, so this one is about 14.5%.

[Cat Whisperer]

I have a Napoleon with 1-7/8 bore - way to big for golf-balls.
I have several mortars with 1.750 bores - that's ok IF you patch them (need to have a VERY smooth bore).
Using 1.72 or 1.73 is much better for unpatched golfballs.

[brokenpole]

Hey Sarge, make sure you post pics of your build as it progresses.  I say that for serveral reasons, mainly if you are doing something that looks unsafe, the folks here will question it and may save you a lot of time and the material you are working on.  Secondly, folks like myself who ain't got a lick of skills working with our hands enjoy watching the progress when someone is building an artillery peice.

Just keep asking those questions!!!! Always remember it's safety first.

[Double D]

I use 24 grains of  Fg and get the magic 30 yards easily.

[theoldsarge]

Wow, really appreciate the drawing of that seacost mortar, that will save me loads of work if I ever get to make one.  And yes, I can see that's good advice, to make the chamber a bit smaller. 
OK, looks like cannon powder might be harder to find anyway, so I have no problem with going with FFFG. 
I am not large on the idea of patching with a golf ball mortar, for my purposes at least.  The range isn't going to be long.  The extra flash will be fun.  And, mostly, I don't want something shooting out that could set dry grass on fire. 

I will be building.  Just don't know when right now.  Wanted to get my homework done first, and I think I've pretty much done that.  Next is finding materials.  That and finishing up some other priorities first.  Among other things I still have to finish a .22 rifle scratch build.  I've not been able to keep going on that like I should have, but as I keep saying, it's a learning exercise as much as a build.  If I knew when I started, what I know now, I would have finished it in less than a week.  But when I do build, I can assure you, there will be pictures.  The .22 build by the way, is being done with metal cutting bandsaw (could use just a hacksaw), drill press (could use just a hand power drill), and files, basically.  I did cut part of my materials from angle iron when I started, but a hacksaw would have worked for that.  I just wanted to see how I would do on a low-tech build.  I could have been neater, but for a learning exercise, I'm pretty well satisfied.