Why would a cannon recoil differently hot or cold???

[Millsman]

In Patrick O'Brian's Aubrey-Maturin books based on navel warfare in the late 18th early 19th centuries on numerous occasions when an engagement is long and drawn out in particular the text remarks on increased recoil as the barrel gets hotter from multiple discharges.   OK. I'm sure this is correct if he says so but how come   ? ??

[little seacoast]

Hi, Speculation leads me to believe that a combination of fouling of the bore and metallic expansion from the heat cause a decrease in windage leading to higher bore pressures and increased recoil.  Now we need someone who actually knows!

[Double D]

Hi, Speculation leads me to believe that a combination of fouling of the bore and metallic expansion from the heat cause a decrease in windage leading to higher bore pressures and increased recoil.  Now we need someone who actually knows!

My speculation agrees with you, plus the the hot barrel would "warm" the powder before ignition and make it burn different, perhaps with more energy. Speculate, speculate.

[shred]

You'd probably also have less friction in the carriage as grease and axles warmed up, which would appear as more recoil.

[Artilleryman]

I know from experience and experimentation that mortar shells travel farther with each shot as the bronze heats up.  It would seem to follow that there would be more recoil...for every action there is an equal and opposite reaction.   My thought is that heat energy is lost to the barrel instead being used to propel the shot.  As the barrel heats up, it absorbs heat energy less readily, and that energy is transferred to shot velocity and recoil. 

[Cannoneer]

Hi, Speculation leads me to believe that a combination of fouling of the bore and metallic expansion from the heat cause a decrease in windage leading to higher bore pressures and increased recoil.  Now we need someone who actually knows!

There's another current thread dealing with shrink fitting pieces of metal tube together; wouldn't the heating of a barrel cause an increase in windage?

[The Jeff]

Hi, Speculation leads me to believe that a combination of fouling of the bore and metallic expansion from the heat cause a decrease in windage leading to higher bore pressures and increased recoil.  Now we need someone who actually knows!

A hot cannon barrel would cause an increase in windage, although the fouling would decrease it. I don't know how much a hot barrel would expand, but I kind of doubt that it'd really make much difference. I agree with Artilleryman that hot barrel = more of the gunpowder's energy propels the projectile rather than warming the barrel.


I've read that old cordite dangerous game cartridges that were loaded in England were loaded with a lower charge so that when they were used in Africa the warmer temperature wouldn't raise the pressure to dangerous levels. Maybe something similar happens with hot cannon barrels.

[Double D]

I do know from our experience at the Montana shoot this past summer that as the air temperature increased and the barrels warmed up loads destined to obliterated Fort  Pallet at 110 yards suddenly were going way over and leaving the range over 250 yards a way.

[armorer77]

In Jan 79 I was in Korea with Mike 3/12 Marine Artillary . Due to extreme cold , +10 to - 20 we were barely able to reach the impact area with our max safe quadrent . Cold powder burns slower . Armorer77

[Cat Whisperer]

In summary:

two things increase pressure:

increase in powder temperature
more fowling decreases windage and increases pressure

Temperature of the metal can go either way - it depends on the geometry of the metal.
If the metal is THIN compared to the diameter the whole thing increases in diameter.  (Example a ring gear on a fly wheel is heated up and shrunk fit onto the flywheel.)

If the metal is WIDE/THICK compared to the diamter the ID gets smaller and the OD gets larger - the metal has to go somewhere when it is heated.  The classic example is the high school physics experiment where at room themperature the 3/4" ball bearing drops through the 3/4 + a few thousandths hole in a 2" diameter disk.  The disk is heated.  The ball will not pass through - until the disk cools.

[GGaskill]

The classic example is the high school physics experiment where at room themperature the 3/4" ball bearing drops through the 3/4 + a few thousandths hole in a 2" diameter disk.  The disk is heated.  The ball will not pass through - until the disk cools.

Interesting if true.  My recollection of the subject was that a hole in a plate was expected to expand as if it were filled with metal.  Sounds like time for an experiment.

[Cat Whisperer]

The classic example is the high school physics experiment where at room themperature the 3/4" ball bearing drops through the 3/4 + a few thousandths hole in a 2" diameter disk.  The disk is heated.  The ball will not pass through - until the disk cools.

Interesting if true.  My recollection of the subject was that a hole in a plate was expected to expand as if it were filled with metal.  Sounds like time for an experiment.

Yup - it is true.  takes 5 - 10 minutes depending on how hot one gets the disk.  (as I recall disk was about 1/2" thick)  It was held horizontally by  a clamp on a typical chem lab vertical post - heated up, ball placed on top and the lecture continued for some time - interrupted when the ball bearing fell through.

Do it - it'll make a believer of you.  Actually you just need to drill a hole, measure, heat and measure again.  Might be interesting to know how much difference there would be between thicknesses.

[GGaskill]

Do you remember how it was heated?  Could the heat been applied mostly around the hole instead of uniformly distributed?

[ironball]

In Jan 79 I was in Korea with Mike 3/12 Marine Artillary . Due to extreme cold , +10 to - 20 we were barely able to reach the impact area with our max safe quadrent . Cold powder burns slower . Armorer77

BINGO! And the opposite is also true. Any reaction proceeds faster at increased temperatures. Not too many years ago, some hunters in Africa found that their super-duper magnum loads developed here in the states would cause cases to stick in the chamber and not eject from their rifles due to excessive pressure. Black powder in rifles, or cannons, must obey the same laws. Pressures go up when the temps rise because the powder is consumed at a faster rate.
 

Hi, Speculation leads me to believe that a combination of fouling of the bore and metallic expansion from the heat cause a decrease in windage leading to higher bore pressures and increased recoil.  Now we need someone who actually knows!

My speculation agrees with you, plus the the hot barrel would "warm" the powder before ignition and make it burn different, perhaps with more energy. Speculate, speculate.

I would be inclined to believe there is not much change in windage. But the higher temps would certainly cause increased pressure due to the faster burning rate.

[Cat Whisperer]

Do you remember how it was heated?  Could the heat been applied mostly around the hole instead of uniformly distributed?

Propane tourch, I think it was steel, well distributed.

[Cat Whisperer]

...

I would be inclined to believe there is not much change in windage. But the higher temps would certainly cause increased pressure due to the faster burning rate.

In general I agree.  On one mortar I have there is minimal (.050" clearance) and heavy loads tend to foul enough to affect inserting the round.  Solution:  wipe the bore every several shots; don't use so much powder.

[shred]

In Jan 79 I was in Korea with Mike 3/12 Marine Artillary . Due to extreme cold , +10 to - 20 we were barely able to reach the impact area with our max safe quadrent . Cold powder burns slower . Armorer77

BINGO! And the opposite is also true. Any reaction proceeds faster at increased temperatures. Not too many years ago, some hunters in Africa found that their super-duper magnum loads developed here in the states would cause cases to stick in the chamber and not eject from their rifles due to excessive pressure. Black powder in rifles, or cannons, must obey the same laws. Pressures go up when the temps rise because the powder is consumed at a faster rate.
 

FWIW, I have no idea about how black powder behaves with temperature (any handy BP target shooter should be able to tell us, and I would expect it to behave 'normally'), but different varieties of smokeless powder can generate less pressure as temperature rises.  My match pistol loads with one of the 'reverse temperature sensitive' powders (IMR 7625) need to be a tenth of a grain higher in summer (100F) than winter (50F) to make the same power factor.  I've done testing with ammo stored in coolers and such like to verify it's not some other factor.

[Artilleryman]

To add to my earlier post.  I did an experiment with a bronze 24pdr mortar.  I carefully weighed my mortar charges so that they would all be the same.  I fired a projectile, marked where it landed, and brought the projectile back to the mortar.  After carefully cleaning the projectile and the bore, I used the same charge by weight and the same projectile to fire another shot.  It went several feet farther than the first shot.  I repeated this procedure and each time the projectile went farther.  The only difference that I could determine was the heat of the barrel. 

Was there a decrease in windage?  If so it wasn't from fouling.  Was there less heat energy absorbed by the barrel as the barrel heated up, and did that energy get used to propel the projectile farther?  I guess I will have to go back to range sometime with feeler gauges to check windage and find out. 

[Cat Whisperer]

Excellent!

[subdjoe]

To add to my earlier post.  I did an experiment with a bronze 24pdr mortar.  I carefully weighed my mortar charges so that they would all be the same.  I fired a projectile, marked where it landed, and brought the projectile back to the mortar.  After carefully cleaning the projectile and the bore, I used the same charge by weight and the same projectile to fire another shot.  It went several feet farther than the first shot.  I repeated this procedure and each time the projectile went farther.  The only difference that I could determine was the heat of the barrel. 

Was there a decrease in windage?  If so it wasn't from fouling.  Was there less heat energy absorbed by the barrel as the barrel heated up, and did that energy get used to propel the projectile farther?  I guess I will have to go back to range sometime with feeler gauges to check windage and find out.

Maybe you could try shooting one round first thing in the morning, cold tube.  Then let is sit in the sun all day, until just after the peak heat of the day (best done in summer, I guess), and then fire one round.

[Artilleryman]

All ready done.  I first noticed the cool barrel vs the warm barrel when we fired our 8 inch seige on a cold morning with our normal charge and the shell only went about 1/2 way to the target stake.  Very embarrassing when you are doing it as a demonstration.  On days when this barrel was sitting out in the sun I noticed that the first shot went long.  Since then I make some adjustment to compensate for this to at least get reasonably close to the stake.