Increase in Force on Sustained Firing?

[Poloxbob]

Hello,

So I have a question related to sustained firing. I was recently listening to an audio book of the Aubrey-Maturin series when they discussed reducing charge to avoid bursting or dismounting a gun based on the observation that the same charge produces more force as the guns heat up. Now, I'll say there is some ulterior motive here as this account in this fictional book is actually quite similar to some results I got testing a medieval Steinbusche (we got steadily more force as we fired and the gun heated up and on about the fifth shot she dismounted from her sled), but at the time I was not aware of this phenomenon. Now that I have heard it, I am wondering if this is something that is real or anyone has heard or read about in any sources I could pursue for future testing.

Bob

 

[tenngun]

Hello,

So I have a question related to sustained firing. I was recently listening to an audio book of the Aubrey-Maturin series when they discussed reducing charge to avoid bursting or dismounting a gun based on the observation that the same charge produces more force as the guns heat up. Now, I'll say there is some ulterior motive here as this account in this fictional book is actually quite similar to some results I got testing a medieval Steinbusche (we got steadily more force as we fired and the gun heated up and on about the fifth shot she dismounted from her sled), but at the time I was not aware of this phenomenon. Now that I have heard it, I am wondering if this is something that is real or anyone has heard or read about in any sources I could pursue for future testing.

Bob

I understand that was a big issue with bronze guns, and early cannon were only fired a few times a day.

 

[Loyalist Dave]

Hello,

..., based on the observation that the same charge produces more force as the guns heat up.

Simple chronographing would prove the fact, coupled with data on the surface temperature of the barrel .

The "force" from the charge would be directly related to the speed of deflagration of the burning powder. Pre-heat the powder, and each individual grain is closer to the "flash" point plus..., you "cook off" any incidental moisture, especially when firing at sea. So the burn rate speeds up, thus giving higher pressures.

I understand that was a big issue with bronze guns, and early cannon were only fired a few times a day.

Which would further the hypothesis, as bronze melts at 1100 degrees lower than iron, so the question might be, does the rise in temperature reduce the tensile strength of bronze or iron significantly to come close to the rupture pressure of the black powder charge used? At what temp does that happen? Does repeated firing of cast iron or bronze weaken either metal when used to contain black powder launching a projectile?

LD

 

[Poloxbob]

Simple chronographing would prove the fact, coupled with data on the surface temperature of the barrel .

The "force" from the charge would be directly related to the speed of deflagration of the burning powder. Pre-heat the powder, and each individual grain is closer to the "flash" point plus..., you "cook off" any incidental moisture, especially when firing at sea. So the burn rate speeds up, thus giving higher pressures.



Which would further the hypothesis, as bronze melts at 1100 degrees lower than iron, so the question might be, does the rise in temperature reduce the tensile strength of bronze or iron significantly to come close to the rupture pressure of the black powder charge used? At what temp does that happen? Does repeated firing of cast iron or bronze weaken either metal when used to contain black powder launching a projectile?

LD

Ahh, now that's what I needed. I am myself not a chemist but a historian, but multiple vectors of attack to think about this issue are excellent because I can enlist the help of people who have more knowledge than myself, and ideas give me a starting point. I have reason to suspect that it is a combination of factors based on the aforementioned testing as it was a reproduction gun milled from a steel billet by a foundry here stateside, so no real possibility of bursting the gun through reduction in tensile strength unless we fired for an incredibly protracted period. However, we did seem to observe this phenomenon, so perhaps we can arrange more testing to confirm or deny questions related to the deflagration as reduction in tensile strength on overheating in historical guns is a certainty. We also had some indications that the modern 75-15-10 powder formulation may not actually be the "strongest" formulation of powder owing to the reaction's dependency on the sulfur and its melting point but is almost certainly the most stable of still efficient powders. I could definitely see it being a more rapid deflagration due to heating of the loaded powder reducing the energy required to hit the reaction point and reduction in moisture resulting in a more efficient burn, but this bears further testing.

 

[springfield art]

Hello,

So I have a question related to sustained firing. I was recently listening to an audio book of the Aubrey-Maturin series when they discussed reducing charge to avoid bursting or dismounting a gun based on the observation that the same charge produces more force as the guns heat up. Now, I'll say there is some ulterior motive here as this account in this fictional book is actually quite similar to some results I got testing a medieval Steinbusche (we got steadily more force as we fired and the gun heated up and on about the fifth shot she dismounted from her sled), but at the time I was not aware of this phenomenon. Now that I have heard it, I am wondering if this is something that is real or anyone has heard or read about in any sources I could pursue for future testing.

Bob

Patrick O'Brien's series is and was totally accurate in every detail. Fiction it may be, but completely based on reality.

 

[64Springer]

Seems to me that the proof testing of the barrel far and away exceeds any minor incremental heating up/pressure increase in a cannon barrel.

It ain't like cannons are rapid fire weapons.

Sea cannons take a day and half to reload. How hot can those barrels get?

With ground pieces, I'd think the wheels would take up the additional pressure by the piece rolling rearward a bit more. But not enough pressure to dislodge the barrel from its trunnions/mounts.

I don't see any cannon anywhere blowing up due to the barrel getting warm and in turn warming up the powder charge.

Defective manufacturing and cast flaws is another story.

.02

 

[IanH]

Sea cannons take a day and half to reload. How hot can those barrels get?.

Where'd you come up with that? Deck cannon were able to be reloaded, aimed, and fired in a couple of minutes by a trained crew. He who could fire the most broadsides usually won.

 

[64Springer]

Where'd you come up with that? Deck cannon were able to be reloaded, aimed, and fired in a couple of minutes by a trained crew. He who could fire the most broadsides usually won.

Your sarcasm detection meter requires calibration.

 

[IanH]

Your sarcasm detection meter requires calibration.

Your sarcasm transmitter requires a frequency adjustment.

 

[springfield art]

Day and a Half to reload? How did they do sea battles with broadsides? This is incorrect, you must look further into that, respectfully. The English were so successful at sea due to constant drill of the gun teams; see Master & Commander movie where they're timed with stopwatch.

 

[springfield art]

Your sarcasm detection meter requires calibration.

Totally missed any sarcasm!

 

[64Springer]

Of course it doesn't take a day and a half to load a naval cannon.

But they are slow to reload. And that's the point. The excessively slow reloading process prevents the barrel from getting excessively hot.

Though not as slow as folks who can't recognize humor or sarcasm when they read it.

Gee Wilikers, Batman.

 

[springfield art]

Cannons were always thoroughly swabbed with the sponge in order to kill embers, too.