Just some quick history on the guns.
6-lb
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12-lb "Napoleon"
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12-lb Howitzer
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6-lb Wiard
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Both sides called the new 12-lb the 'Napoleon', after Napoleon III (gun designed in France).
I classify the 6-lb as 'smoothbore' as it represents the gaggle of different 6-lb smoothbore artillery used by the South (veterans of the Mexican-American war, and earlier), which were generally discarded by the North.
The Confederates tended to base artillery batteries off the mix that used to be commonplace in the Mexican-American War (so many 6-lb field guns, and 12-lb howitzers). The Union was better able at replacing its artillery (no 6-lb or 12-lb Howitzers served out East, and only a few out West), as the 12-lb Napoleon was a field-howitzer, capable of filling the roles of the 6-lb and old 12-lb, and do both jobs better.
The 6-lb should almost be exclusive to the South, representing their mixed batteries of 6-lb field guns and 12-lb howitzers.
Most Southern Artillery ended up being captured Northern Guns (Their produciton was dwarfed by Northern production, and individual quality was much poorer). This is why armaments between the two ended up being so similar.
Another issue, not discussed yet, is the fact that the majority of Confederate batteries were of 4 guns, while the majority of Union batteries were of 6 guns. Also, Union powder was more effective (longer ranges, more accuracy, greater amount, etc.). Currently, Union Artillery has slight strengths over Confederate Artillery, but I think it may need to be greater. Also, their artillery men were renowned. One Confederate General said, take Southern Infantry, and Northern Artillery, and that commander could conquer the world.