From the Designer's Notes:
"I wanted a rules set that could simulate this incredible conflict, yet still be easy to learn and fun to play. I also attempted to keep casualties realistic. That is why I chose the D20 as the combat die. It is not easy to inflict casualties in Guns of Liberty, but morale plays a decisive role in the game. The quality of forces can make up for lack of numbers, while militia poses a wildcard. With they stand and deliver or will they scatter at the first sound of the guns? The variable Fire, Melee, and Morale values allow to make mild, yet significant, differences between troops."
More information:
Guns of Liberty is designed for 15mm miniatures. One inch on the table equals 25 yards. Each figure represents 20-25 infantrymen, 10-15 cavalrymen, and each artillery crew represents one gun, with the artillery gun itself notating the location of the section.
For 15mm, infantry and cavalry stands are 1" with with two figures. Alternative basing is given for 6mm and 25mm figures.