Pardon me if I find it hard to understand why the Gatling Gun is included in the game and the Williams Gun is not.
The only Gatling Guns to see service were those 12 guns purchased directly by Gen. Ben Butler for $1,000 each and confined to the Petersburg front, where only 2 guns were used, of these 8 seemed to have been mounted on gun boats. These guns had a rate of fire of 150 rounds per min. and not the later 350 of the 1865 model that was not delivered in time to see service.
The Williams Gun was brought into Confederate service in the autumn of 1861 and 7 Batteries were fielded. The gun had a rate of fire of 65 rounds per min. but it had a 1 lb projectile of 1.57 inch caliber. Roughly 3 times the size of the .58 Gatling Gun which would make it far more effective against fortifications, buildings, and so on.
These were 6 gun batteries except for one 4 gun battery. It was seemingly better than the early Gatling Guns, having only a problem with overheating at high rates of sustained fire, where as the early models of the Gatling had quite a few draw backs. Remember this is not the gun the US Army excepted into service in 1866.
It was light and usually drawn by only a single horse and was said to be an excellent Cavalry support weapon.
Sometimes it is odd that we have one impression of history when in actuality it was much different.