Cannons of the Seventeenth Century
The main changes in the 17th century involved sizes and numbers. European ships were now carrying as many as 100 guns on three separate decks. 42 pounder guns were often the standard gun on the bottom decks. Special shots or artillery rounds were being developed especially for naval use. Barshot, chain shot, were rounds designed to destroy rigging and sails. Bundle shot, canister, grape shot were used against personnel. Cluster rounds and Sangrenel rounded out the variety of shots fired from the Cannon. (See below for a fuller treatment)

Cannons of the Eighteenth Century
Ships of War had improved dramatically by the opening of the 18th Century, In fact, the Golden Age of Piracy was probably the Golden Age of Sail as well. Cast Iron muzzle loaders ranging from the small 6 pounders to the large 32 pounders were the general rule. Elevation was adjusted by a modified quoin under the breech and the general science of trajectory was better understood. Fixed loads of powder were calculated for the guns improving accuracy and the guns were secured to the sides of the ships by heavy breech ropes passed through or around the casabels, limiting recoil and aiding in the reloading of the guns. Side tackles were also added as well as small ramps behind the guns to aid in pulling them back into firing position.

The Naval Artillery had unheard of range of about 2,000 yards (meters) by this time. Of course most engagements were fought at under 1,000 yards and sometimes within pistol shot (25 to 50 yards) The only innovation in artillery rounds for this time period was the art of heating solid iron shot to a red hot condition before firing the round. It was a tricky affair, because the heat of the hot iron could cause a cook off, that is an early discharge of the cannon, thus killing your own cannoneers. The usual method for firing red hot iron was to swab the barrel with water then dry the inside, add the powder, followed by a plug of wood and then the loose fitting hot iron. The purpose of using the hot iron was to set the other ship on fire.

The art of explosive shells also came of age. An explosive cannon ball fitted with a timed fuse would be fired from the gun. If the timing was done properly, the shell would explode when it reached the other ship. Some of the cannons began using a flintlock mechanism for firing instead of the flaming torch that is used in so many movies. The torch could be used but the flintlock was more reliable and much safer. The mechanism worked by pulling a lanyard instead of a trigger.

The term "pounder" refers to the size of a gun. A six pounder fired a solid shot of lead which weighed approximately 6 pounds. A 32 pounder fired a ball of lead that weighed approximately 32 pounds. Although this makes the identification of a cannon's power very simple, it says little about the approximate weight of the cast iron gun. For Instance:
 

Type	Bore Size	Gun Weight	Shot Weight
2 Pounder	2.5 Inch	600 lbs	2 pounds	3.5 pounds
6 Pounder	3.0 Inch	1,000-1,500	6 pounds	6 pounds
24 Pounder	4.5 Inch	3,000-4,000	24 pounds	14 pounds
32 Pounder	5.0 Inch	4,000-5,000	32 pounds	18 pounds

As you can see the weight of the cannon had to significantly increase as the size of the shot increased. However the weight ratio of powder to shot decreases as the shot gets larger. Most of the weight of the gun is centered around the breech of the gun where the explosion takes place and most of the pressure is exerted. Guns wore out relatively fast, usually being good for 500 to 1,000 shots before being rendered unsafe to use anymore.