Does anyone know the technical difference between a gun and a cannon? While this sounds obvious, I recently visited a fort with some multi-ton guns that are NOT cannons (circa late 1860s), but I forgot to ask what the difference is! Maybe some Civil War buff-SDoper may know… - Jinx
I was told the difference is that while a cannon is a smoothbore weapon, a gun has lands or grooves which impart stabilizing spin to the projectile.
I don’t think there is a complete distinction between cannon and gun. Automatic guns mounted on aircraft get called cannons. Howitzers and other mounted artillary are often called cannons, but ship board gun systems are generally called guns.
I have seen dictionary definitions that describe guns as being large-bore rifled weapons, but that is contradicted by the multi-barreled cannons on aircraft. Also I’ve seen a definition that anything over 20mm is a cannon, but naval and coastal guns are generally not called cannons.
My own working definition, if the distinction is really important, is that they’re both large-bore weapons but cannons are used in direct-fire mode (aimed) while guns are used in indirect-fire mode (plotted).
The ‘anything over 20mm is a cannon’ thing might arise because 20mm is generally regarded as the smallest practical caliber for explosive shells. (Cannons generally fire ‘shells’, guns generally fire ‘bullets’, not vice versa; there are other terms for their ammunition, though.)
Whether or not something is rifled doesn’t, AFAIK, make it a gun or a cannon. I’ve even heard the term ‘smooth-bore rifle’ for a gun that looks like a rifle and has a caliber of around 5-8mm but lacks a rifled barrel.
Howitzers are called that because they are fired at high elevation, resulting in a high trajectory but a shorter range than something fired at a lower angle. Most likely, a howitzer is anything that fires above 45° elevation, since the maximum range for a projectile is achieved at that angle. Mortars are also fired at high elevation, but they’re an entirely different type of weapon.
NattoGuy: It might be possible that the ‘cannons’ on aircraft were called that to distinguish them from machine guns; many WW2-era aircraft had both cannons of around 15-30mm (most often 20 or 30mm) and machine guns (.30 cal or .50 cal or something close). Modern multi-barreled guns on aircraft are cannon-sized, though. They generally don’t fire explosive shells, although WW2-era cannons usually did.
The “real” answer is liable to be based a lot on context.
I have seen, for example, one definition of cannon indicating that it is a gun on wheels. Based on the OP, I am wondering if the distinction made was that coastal defense guns are often mounted on fixtures, rather than on wheels. It is not a very common distinction, however. (And I have been to any number of historic sites where the guides and the information displays are in error, so that is a possibility.)
The more likely explanation for a fort from the 1860s would be a distinction between “cannons” (smoothbore) and “rifles.” With rifling being a new technology (for large bore weapons) at the time, the various weapons were often referred to by that nomenclature. I do not know of a cannon vs gun distinction, however.
I suspect that the distinction of terminology referring to the weapons aircraft carry (and the land- or ship-based anti-aircraft weapons) are distinct from the rules defining heavy ordnance. (I’m pretty sure that the earlier posts are correct that above .50 caliber/12.7 mm, automatic weapons were called cannons by analogy because they were capable of firing exploding rounds, not because there was anything intrinsically “cannonish” about them, and, as noted, the technology for automatic weapons has undegone a great change since the early 20th century when the terms were established, making some old definitions obsolete.)
Among large bore weapons, there are three general classes. Long guns or cannons have a longer barrel and shoot a round in a flat trajectory. Howitzers have slightly shorter barrels (which means the round moves more slowly) and are generally fired in a higher, curved trajectory (good for shooting over hills). Mortars are short barreled, low charge weapons intended to shoot very high trajectories. The mortars of the Civil War era were short, squat bowls of iron with incredibly thick walls used to bombard forts. Modern mortars are generally infantry support weapons: the light charge means that they can be built lighter (the barrel does not need to be so thick) so that troops can drag them into the field with them. The high trajectory means that they use the earth, itself, to absorb recoil, so there is no need to build in recoil dampening fixtures (with more weight).
But which is better for hunting Wascally Wabbits? Guns or cannons?
I agree.
The military has/had a tank-looking thing called a “self-propelled gun”. It’s a huge gun one can drive around apparantly.
I’ve always called anything really huge with Fixed Ammunition, a Gun. No matter how big, or whether it was rifled.
If it gets stuffed, I call it a cannon. Except those WWII things that were towed by Jeeps. I don’t know what kind of ammo they use, but I call them cannons.
Rule of thumb: You can call anything a “Gun” if it is larger than a pistol or a rifle. People will accept that, I’ve noticed. But if something is popularly referred to as a “Gun” and you call it a “Cannon”, some people will freak out on you. Oh… but don’t call your M4 or M9 a “gun”. You have to call those “rifle” and “pistol” respectively or people will freak out on you.
Man. . . I hate these people.
Cannons are guns but not all guns are cannons. Cannons are mounted guns as opposed to ones you carry around. In German, the most generic term Kanone refers to either such as the dreaded Kartoffelkanone.
Potato Gun?
A few years ago, a German TV program, Der Spiegel TV, televise a story about potato gun - Kartoffelkanone, causing mischievious pranks and vandalism. Overnight, its website crashed because of the number of kids logging on to find out how to build or buy one. Very similar to what 60 minutes did in the sixties - they did a segment on glue sniffing, the following months, gluesniffing had become a phenomena across the country.
So an ATG (Anti Tank Gun) is a cannon 
Just to add to the confusion I have heard of a battleship’s main batteries (the really big guns) referred to as naval rifles.
cannons although they fire explosive shells, they generally have a slower rate of fire than your average machine gun. and since wabbits are quick and tricky creatures, the high volume of fire would be a definite plus. since ww2 has come up, i recommend the p-47 thunderbolt fighter plane, with 8 machine guns, it could put over a pound of lead on a target with a 60 second burst, or so my memory recalls.