Nicely done --- the gun carriage is American, 2 tails, and was heavily influenced by late 18th century French design. By this time, the British gun carriages were more advanced, lighter and had a better weight distribution with a single tails --- making them more mobile. At the same time, the quality and understanding on how to manufacture high quality iron cannon was increasing - saving considerable weight, when compared to "bronze" cannon. The 8-pounder is an American/French gun. The British would have been using a 9-pounder.
In the late 17th century and early 18th century, bronze cannon were considered to be much more dependable than iron cannon due to an incomplete understanding on how to best manufacture a iron cannon. Both the bronze and iron cannon could misfire and explode, but the resulting shrapnel from an iron cannon failure was much more deadly than with a bronze failure. If I remember correctly, the British at Fort William Henry lost more the 50% of their iron cannons due to misfires and exploding barrels.