Stan,

In responding to this I realized that I neglected the key difference between a howitzer and gun: the howitzer has a powder chamber while the gun does not. At one time such characteristics went hand-in-hand with the high angle fire of shells instead of solid shot, but by the time of the war these distinctions were breaking down in a multitude of ways. So it would have been more accurate for me to refer to the Woodruff's as guns because they lacked powder chambers rather than because of their caliber length.

Technically, the ACW period "gun" was 15 calibers long or greater (with 27 calibers being the upper limit because it began to have negative effects.) It also was not supposed to have a powder chamber. "Howitzers" were less than 15 calibers in bore cylinder length. Sounds simple enough, but this rule was being heavily violated in the years just before the war and of course throughout the war itself as I'll point out below.

There was the Napoleon, a "gun-howitzer". Its cylinder bore was 14 calibers long. However, it lacked the powder chamber. So it was a marginally too short gun. Smoothbore "guns" of the traditional definition were obsolete. They were replaced by the gun-howtizer and rifled artillery.

The really big pieces like Columbiads got even more confusing. The original types in the decades prior to war were chambered seacoast howitzers. Then came the "New Columbiads" produced just before the war. They were not chambered, but their cylinder length was only 10-14 calibers. The big Rodmans had no chambers, and bore lengths of 10-14 calibers. So they were not howizers but they didn't fit the traditional criteria of guns either based on length.

Then there are the big naval Dahlgrens shell guns. These had gomer chambers rather than the smaller cylinder chamber typical of howitzers. They were short tubes of as little as 8.7 calibers on the 15 inch.

And there are more bizarre combinations as well, but I'll stop here with the short tube length guns.

Mortars had far shorter caliber tubes than howitzers of course. They had chambers in the older types--a shared feature with howitzers. (The newer 1861 models had a hemispheroidal chamber such that it doesn't look much like traditional howitzer/mortar powder chambers--and was both more efficient and stronger than the old pattern.) Mortars were designed primarily for firing with varying powder charges at fixed elevations of ~45 degrees.