What do you think 2.7 to 3 inch bore? Trunnions are so long that it must put a lot of strain on whatever means of attachment he is using. My 10 pdr Parrott has a three inch bore, but the barrel weighs 900 lbs which helps to dampen the recoil.
Cat, you are right in that the recoil systems changed. The recoil system for the old guns was for the carriage to take up the recoil as it rolled backward. The obvious problem with that is that you had to roll the gun back into battery and re-align and sight it which took time. The advantages of having the gun roll back would be that if you were firing from an embrasure or gun port you have access to the muzzle of the gun for sponging and loading. Also in field artillery if you were hard pressed by the enemy you could retreat by recoil, which is to fire let t he gun roll back reload and fire again each time from a position further to the rear (about 5-10 yards each time depending on the ground).