A Question On Gunnery

If you’ve read, CS Forester, Patrick O’Brian, etc., one phenomenon you read about over and over is the notion that a hot cannon tube shoots farther than a cold one.

I’m hesitant to challenge a recurring theme in naval fiction but I find it hard to believe that this is true.

By way of biography, I’m a former infantry officer with quite a bit of experience in cannon gunnery both as a platoon leader for a 4.2″ (or should I say 27-pound to stay within the spirit of this blog) mortar platoon (that is not me in the photo) and in calling in artillery fires.

There are various interior and exterior ballistic factors which determine how far a gun will shoot. Primary among them are weight of the projectile (or projo, in the vernacular), the amount of propellant used, length of the gun tube as a factor of the projo diameter, etc. In the age of muzzle loaded cannon, gunners also had to contend with variations in the bore of the cannon caused not only by imprecise manufacturing techniques but the erosion of the bore caused by the hot gases produced by burning powder, variable diameter shot, different grades of gunpowder, etc.

When dealing with one gun, one can assume away most of the ballistics as mathematical constants, leaving us to ask why would a hot gun toss a projo farther than a cold gun. A hot gun tube, especially a brass or cast iron one, is going to expand increasing the bore diameter in a small way and thereby increasing the amount of hot gas propelling the projo down the tube. The only factor I can see that a hot tube would positively affect would be propellant temperature. Warm propellant burns hotter and more efficiently than cold propellant. I doubt whether a powder charge would be in a tube long enough to become heated before it was fired.

With modern artillery it is axiomatic that a cold tube will shoot farther than a warm one. One wonders why this would be different with a muzzle loaded cannon.

1 Comment

Filed under Naval Weapons

One response to “A Question On Gunnery

  1. Ben

    Could it possibly be that when hot the metal expands slightly, it expands inwardly and outwardly, in fact reducing the windage of the gun? Which in turn would increase efficiency and thus range?

    I’m no expert though, just a thought…

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