what makes a cannon loud?

[Cat Whisperer]

A recovered golf ball (ok sample of 1) from a mortar I fired was blackened only on one side - indicating very little if any 'rolling' in the tube.  I'd like to see more samples and from longer tubes.

[gulfcoastblackpowder]

If it doesn't roll, perhaps that's why it bounces...

We know for a fact that there are multiple forces operating on the ball - the explosion pressure front, gravity, and friction.  We also know these are acting (in various magnitudes) in different directions.  This means these forces impart a torque on the ball, if not a spin.  The torque alone, even restricted from spinning, may be why the balls bounce.

[bluez]

A recovered golf ball (ok sample of 1) from a mortar I fired was blackened only on one side - indicating very little if any 'rolling' in the tube.  I'd like to see more samples and from longer tubes.

Remember that golf balls are not solid objects, take a look at this:

http://www.youtube.com/watch?v=AkB81u5IM3I


In fact when the powder is starting to push the ball down the barrel, the golf ball is most likely expanding and pushing itself hard against the walls.

Another example is vine corks, i am using them in my small 22mm mortar to add resistance in the barrel when i am shooting blanks. This corks are 1mm smaller then the barrel, still they work perfectly. I can only explain this with the fact that when the gases starts to push on the cork, it starts to expand and are holding back by pushing against the barrel.

[Cat Whisperer]

Maybe they expand inside the bore.

I've not seen evidence of skuffing around the circumfrence, which would indicate expansion.
I have seen, with heavier charges, cans and bottles expand to skuff the bore (when filled with water).

My THEORY is that there is plenty of clearance (windage).  The ball starts against one surface (gravity effect) and is 'centered' by the gasses passing around it, but it keeps in motion to hit the top, then bottom of the tube on the way down range.  Pure supposition (PFS).  Location of dings inside the bore would prove/disprove it.

[Parrott-Cannon]

I've noticed that the ring occurs when the wall thickness is thin.  (at least two of my mortars ring - both steel)

The ringing effect is dependent on the material tickness and the modulas of elasticity for the barrel.

Which is to say they likely all ring, but most are rigid enough (from thickness OR material) so that it isn't loud enough to perceive considering the other atmospheric disturbances.  Thanks for adding the term modulas of elasticity - that adds to our knowledge base.

To complete the addition to the knowledge base, for those who may not be familiar with the term, modulus of elasticity, spelled with 2 u's and no a's, indicates the ability of a material to strain (or stretch non-permanently) under stress.

While you are right, that all cannons will ring to some degree, some materials lend themselves more to it than others.  The lower the modulus, the easier it is for the material to flex under loading.  This flexing and is what causes the vibrations Parrott referred to, and is what causes the gun to ring.  For instance, Brass has a Young's Modulus of 100-125 while Iron and Steel are 190-210.  That is why, for a given geometry, a brass cannon will sing more than a steel or iron one.  

Of course, the vibration of the gun isn't the cause of all the noise from firing a cannon - most of the noise is from the powder and the conditions of it's use (grain size, volume of powder, wadding, bore size, bore length, etc.).

Thank you correcting my spelling.  I am the worlds worst speller.  What I do not understand is why the ball bounces in the barrel.  Conservation of momentium sugests that a smooth ball fired from a smooth barrel would simply role down the barrel.  I do known, the roughness of the barrel and ball play a major role in the velocity a cannon acheives.  I have a golf ball parrott and a golf ball french 75.  The parrott produces a velocity of 672 fps while the french 75 acheives a velocity of 811 fps using golf balls for ammo and a 400 grain charge of cannon grade powder.  The barrel on the parrott is rough while the french 75 has a very smooth barrel (the friction factor).  Do you find more ringing with smooth barrels?

My parrott has a heat fitted band and produces high pressure reading that do not reflect the powder charge.  I beleive this is cause by amplication of the ringing caused by the bell within a bell effect of the band construction.

Thank you, sound like a good explaination!