I'm using Sash and Saber guns for my armies, as no other manufacturer's guns are big enough to pass for Civil War artillery. (Foundry comes close, but Foundry guns are $15.50 each!) Look at these Federal officers with this 3" rifle. The wheel comes up to their shoulders.
I'll be using "Guns at Gettysburg" for my 28mm tactical ACW battles. GaG is very specific about performance of particular guns. It really does make a difference if that gun section is armed with a 10-pdr Parrot or a 3" ordinance rifle. I don't want to paint up 60 gun crews to cover all the possibilities, so I settled on painting a crew base with no gun!
When I need a specific gun, I can add it to the base. Fortunately, Sash and Saber uses the same carriage for all its guns, so figures who are interacting with the guns (like the man here stopping the vent) will look natural with all of them.