I also wondered why the range tables always gave the range at a 5 degree elevation. Since this question was never answered in any artillery book that I read, I finally concluded that this was their traveling position for the tube and was also the most used elevation when they went into action, in effect their fighting position. You mentioned 4,200 yards of range, Civil war artillery seldom fired in the high elevation settings. This type of field artillery was a line-of-site weapon, they had to see their target to lay the shot and to make corrections for following shots. General Henry Hunt, the artillery commander of the Army of the Potomac said a human figure could not be seen after 1,200 yards so to fire at a greater range would be undirected fire with very poor results. Actually, during the civil war, 80% of all firing missions was at ranges less than 800 yards, despite having the ability to fire at longer ranges. The most common range used was 600 yards. Field artillery remained limited by sight not range until the invention of the field telephone. This occurred in world war one. With the research and improvement in the guns, the lack of a cushioning system for the guns was solved by the invention of recoil cylinders. Thus was born the modern field artillery of today.