New to the group. looking for info, and advice.

[john pike]

Hi all, i got a bug up my but to build a cannon, ive built telescopes for five years on my lathe and mill,
i had a piece of stainless steel kicking around so i made a morter,
sub-chamber is 1/2 X 3/4 deep,  front chamber 1 and 3/8
over all length, 4inches, 2 1/4 diam over all.

i fired it without anything in it, ffg half of the chamber,,woosy,,,
fired again full, with toilet paper wadding, Pop,,, cool,,,

then i found out that a PVC round end-cap slides into it nicely,
loaded tiny bit of toilet paper in the powder chamber to keep it in,
lowered it level at my chain link fence,
BANG,,, little louder than a fire-cracker,,, end cap flew 20FT,

another round straight up, full load, 40FT, cool,

NOW, ami gonna blow my self to bitts using stainless steel??

i am also looking for info on building a Howitzer out of 1018.
4inches in diam, and no longer than 18 inches, its all ive got on my lathe
for room.
how large of a bore can i safely have,

id idealy want something that booms or cracks louder or as loud as a M80
so im all ears for advice,

i cant shoot beer-cans as i live in a couldisack, but want something for the 4th, and newyears,

thanks for listining, hope im not comeing across like the idiot i am.

oh ya how do i add a pic of my morter???

clear skys, johnp

[Cat Whisperer]

John -

WELCOME to the board.  

PVC is what I use filled with concrete.  (4" diameter 4.500" OD and weighs 7.5 lbs).  

Occasionally on third or so firings a piece will crack off - something to watchout for.

Stainless - what kind, could easily be 303 - easy cutting, 304 is much harder and there are easily a dozen other types.  With good design of the interior, powder chamber and thickness WITH reasonable loading and light bullets you'll be OK.  Use a slow powder to keep pressure down, faster to make a bomb.

Look at existing proven-safe designs & copy one - that's the easy way to design.

[GGaskill]

Those dimensions shout "1/2 scale Mountain Howitzer."  See One of my half scale mountain howitzers for one version.  It could be bored for golf balls or 1 lb spherical lead sinkers.  You'll need a 36" lathe to be able to bore it, though.

Check out the stickies at the top of the forum on picture posting.

[john pike]

Those dimensions shout "1/2 scale Mountain Howitzer."  See http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=58644" target="_blank">One of my half scale mountain howitzers for one version.  It could be bored for golf balls or 1 lb spherical lead sinkers.  You'll need a 36" lathe to be able to bore it, though.

Check out the stickies at the top of the forum on picture posting.

Would you happen to have any demensions? or plans?
i could download??

thanks
johnp

[GGaskill]

I have a .dwg file I can email if you have software to read it.  Otherwise, I can snail mail a print.

[john pike]

I have a .dwg file I can email if you have software to read it.  Otherwise, I can snail mail a print.

Yes please send it, my wife does autocad so she'll print it out for me.
send it to me here,
dont mind the adress, i spend alot of time in the ditch with my jeep,
,
dirtyditchdawg  at  gmail.com  do the funny "at" replacement.

johnp

[GGaskill]

On its way.

[john pike]

On its way.

Again thank you very much.

maybe ill do two, scale one down small enough for brass,,expensive stuff,,,,

johnp

[GGaskill]

I did a quarter scale one in brass.  Cost $40 for the brass; a half scale steel one cost about $55.

[john pike]

I did a quarter scale one in brass.  Cost $40 for the brass; a half scale steel one cost about $55.

"G", whats your recomended load for your 1/2 scale Howitzer?
and for the 1/4 scale brass,

thanks
johnp

[GGaskill]

Charge depends on bore and chamber size and shot weight, barrel robustness, and powder granulation.  If you use the bore/chamber dimensions on the half scale print (1.5" bore/1" chamber, steel barrel), I would say you could safely load one ounce of Fg as a blank charge and maybe as  much depending on shot weight.  

My brass one has a 3/4" chamber and 1" bore.  I haven't determined a charge for that yet.  I plan to start with a chamber full of FFg and a 1" ball bearing and see what happens.

[john pike]

Charge depends on bore and chamber size and shot weight, barrel robustness, and powder granulation.  If you use the bore/chamber dimensions on the half scale print (1.5" bore/1" chamber, steel barrel), I would say you could safely load one ounce of Fg as a blank charge and maybe as  much depending on shot weight.  

My brass one has a 3/4" chamber and 1" bore.  I haven't determined a charge for that yet.  I plan to start with a chamber full of FFg and a 1" ball bearing and see what happens.

Thank you ill be building it to your specs, except maybe some fancy detail work,

johnp

[Cat Whisperer]

....
  I haven't determined a charge for that yet.  I plan to start with a chamber full of FFg and a 1" ball bearing and see what happens.
....

For those of you less experienced than George, take a hint from The More complete Cannoneer, 3rd Ed. by M.C. Switlick, pg. 105:

"Whenever a person begins cannon shooting, it is prudent to start with an abserdly light powder charge."

Bold letters are his emphasis.

[GGaskill]

It IS a good idea to start with a less than maximum charge.

johnp--make sure you can find some shot that fit before fixing on 1.5" bore diameter.  If you use golf balls as projectiles, their low mass will limit pressure.  If you use 1 lb spherical sinkers (about the same size), you will get higher pressure.  But either would be safe with the proper charge.

[Double D]

George,

Brass?  What brass are you using? Where can I get it?  I have always been lead to believe that most brasses do not have sufficient strength for cannon use.

[GGaskill]

It's supposed to be C36000 free-cutting brass which is pretty good material.  But the design specifics (chamber/bore diameter, wall thickness, etc.) and firing circumstances (powder charge weight and granulation and shot weight) are as important in determining safety as the material characteristics.  Assuming a chamber pressure of 20Kpsi, the thickwall cylinder stress formula gives a stress value of 31,800 psi (at the inside wall; it goes down as you move toward the outer wall), which is well inside the values for C36000.

[Cat Whisperer]

I agree with the raw pressure calculations of being within the normally assumed pressures of blackpowder.  I raise the question of repeatablity - does brass (as opposed to bronze) survive the repeated hammering without hardening and loosing it's ductility (resulting evenetually in brittleness and cracking)?  Just raising the question.  The answer lies in others' repeated success over many firings over time.  If there are some that are concerned about it, it may be because of observed failures.  Both cases are worth investigation.

[Double D]

If the the minimum recommended strength of a seamless steel liner for a cannon tube is 80,000 psi how can 31,800 psi brass be safe.  

Is there something about the metalurgical properties that I don't understand?

[GGaskill]

31,800 psi is the calculated stress in the material caused by firing (assumed pressure of 20K psi).  The material characteristics are 58,000 psi tensile and 45,000 psi yield (from the Anchor Bronze website).  This gives you a 40% cushion and, according to my ballistic engineer friend, you're OK even when the calculated stress is at the yield point, because that stress is at the inside surface and it decreases as you move toward the outside.

The use of high strength liners allows them to be thinner, which is important when you are trying to maintain the original exterior profile.  The actual stress induced by firing is dependent on both the thickness of the liner and the bore diameter.  South Bend Replicas recognizes this by using liners of increasing thickness as the bore diameter increases.  It is also one of the problems with the rules, as a 3/8" thick liner may be fine for one bore size but woefully inadequate for a larger one.  "One size fits all" doesn't work well here, either.

[Double D]

Again slightly reworded,  if the minimum  recommended size of  seamless steel liner for a cannon tube is 3/8 inch rated at 80,000 psi what is the minimum thickness brass tube you need to meet that 80,000 psi?

[GGaskill]

The problem is there is no "one size fits all" answer.  The stress in a 3/8" wall tube 2" in diameter at 20K psi internal pressure is 53,300 psi.  For a 4" diameter tube, the stress is 106,700 psi.  The first is within the 80K psi strength of the steel tube; the second obviously is not, so that application would require a thicker tube to prevent yielding of the tube.  The same principle goes for brass except the material has a lower strength so it requires thicker sections (walls) to lower the stress under the strength of the material.

I hesitate to post the formulas (although they are available on the internet if you look for the right thing) for fear that people will use the formulas without integrating other knowledge, but here they are:

Thick wall cylinder hoop stress:  s=P(R*R + r*r)/(R*R - r*r)
where s is the hoop stress, P is the chamber pressure, R is the exterior radius and r is the interior radius.

Thin wall cylinder hoop stress: s=Pr/t
where s is the hoop stress, P is the chamber pressure, r is the interior diameter and t is the wall thickness.

I used R*R for R squared since I can't post superscripts on the board.

[Cat Whisperer]

I think there is agreement that the numbers spit out from the formula have an appearance of validity - the nominal blackpowder pressures are relatively low compared to the strengths of materials.

However that's not the point in question.  Of course varying diameters will have different stress levels and other features can readily cause stress risers.

The issue here, as I see it, is that one or more organizations (N-SSA of note) has laid out a MINIMUM specification for a steel liner that BOTH a) excedes the strength of the material chosen (brass) and, b) there is reputation that brass has of being less than suitable even compared to bronze (which also would be required to be steel sleeved by N-SSA).

The issue is not that the brass cannon would or would not survive one or more firings (even with no measurable dimensional changes), but that the material chosen MUST be proven over many firings over time to be reliable.  Were looking at the difference of brass and bronze and the ability to retain strenght and ductility.  Those issues are NOT addressed by the formulas.

I think it would be foolish to endorse ANY material for serious cannon making (except for the minimal pressures of something like a golf-ball mortar) until proven by a process of testing that verifies that what really looks good (brass) is in fact reasonably safe.

[Double D]

Not looking for a one size fits all just a minimum...what is the minimum wall thickness for a brass cannon?

[GGaskill]

DD--I can't give you a number like that as the thickness will depend on the inside and outside diameters over the chamber.  Work the formulas above and juggle your dimensions until the calculated stress comes out at a level you are comfortable with.  I am satisfied with 31,800 psi for C36000.

CW--I agree that extended testing is the way to go, especially since we are missing some important information (primarily chamber pressure numbers for the configurations we are using.)  However, US bronze artillery was made from 90/10 tin bronze (similar to C90700) which is barely half the material that C36000 is.  I realize that brass work hardens (which strengthens the material as well as reducing its maleability) but there are brass cannon on the record (both old and modern repros.)

[Cat Whisperer]

....
 I realize that brass work hardens (which strengthens the material as well as reducing its maleability) but there are brass cannon on the record (both old and modern repros.)

That is EXACTLY the point!  When it hardens, strength is less important BECAUSE the repeated firng WILL start a crack.  It's just a question of time.  That's why the steel liner is critical.

There are some things that you can 'get away with' for quite some time.  

There are some practices that one does because it prevents the event that happens occasionally or rarely.  That is the path that is path we recommend and that organizations like N-SSA and AAA demand for their competitions - based on experiences - good and bad.

Obviously I do not want ANYONE to repeat my observation of a cannon exploding.

[Double D]

Work hardening is what make the necks split in cartridge brass.  

Back in college Federal cartridge funded an experiment I did for a term paper on brass hardening from repeated working caused by firing, resizing and refiring until the brass failed.  That was 20 some odd years ago and all I remember was that annealled brass didn't get splits and work hardened brass split fairly fast.

Of course this was cartridge brass.  

Just the same, I have to yet to learn what the parameters are for safe use of brass in cannons.  

It's not lost on me that both N-SAA and AAA don't allow brass guns.

Lacking sufficient evidence to show what brass will sustain 80,000 psi,  I say would use brass for cannons at your own risk.