Mostly officers and cavalrymen. Early in the war many infantry on both sides had personal sidearms or even big bowie knives (for the Confederates). After a long, hot, tiring march, they learned to toss it away as excess weight.
Infantry had enough to carry without the weight of the personal weapon.
This is so very true. I have read a bunch of Civil War Autobiographies/Reminisces. Just finished one by General E P Alexander.
http://en.wikipedia.org/wiki/Edward_Porter_Alexander Very few CW reminisces were written by privates.
Officers were primarily expected to direct and lead their men. For that reason Infantry Officers typically carried swords as a badge of office, and revolvers as a personal weapon. Infantry Officers more often used their swords slapping slaggers with the flat of the blade then they did cutting or stabbing the enemy. General E P Alexander often “borrowed” a service rifle to pot shot at Union soldiers when he was not aiming Napoleons at them.
Cavalry had their horses and while sword use happened quite frequently, in mêlée combat the most dangerous weapon was the pistol. Later, as the war progressed breech loading carbines starting pushing the engagement distances of Cavalry out and that firearm began to change Cavalry tactics.
In today’s world were we sit on our butt and drive everywhere weight is not an issue. However back when you carried everything and marched 10 to 20 miles a day, weight was a real issue. Lucius Barber, a Union Private who wrote "Army Memoirs" added up all the miles he marched, and it came to be 10,897 miles. If you are going to march 10,000 miles carrying a combat load of 60-100 pounds, you sure are not going to add weight if you don’t absolutely have to.
As to what caliber was carried the most, someone would need production records to determine that. From what I have read, Cavalry were happy to have either. Infantry, if they carried a personal side arm, was very likely to carry a pocket pistol. There are lots of 22-32 rimfires around from that era. These were small underpowered pistols, but the important thing was they were small.