Tom
Rifle Ball generally refers to an elongated-conical projectile.
Buckshot wasnt as commonly used as others, but it was still out there. Ord records and battlefield excavations tend to suggest it was used more than most people think of it. Many have assumed it was favored predominately for close in use when guarding fortification causeways, bridge crossings, or massed enemy within short range. Also what we would sometimes call shock-troop assaults. Might not inflict immediate fatal wounds, but definately ruined the day for a couple guys with one pull of the trigger. Stunned, disabled or stalled from being able to immediately shoot back at you. Buck from Buck-in-ball did scatter somewhat but not as much as normally expected.

Many have examined medical and casualty records before, each taking a different task or angle for research study (Myself included). The further you dig, the more varibles come to light and into play.

One can get a general idea of what the mortality rate could be from a given projectile type hitting a specific part of the body based on the surgical case reports. When taking the angle of an overall given engagement it gets a bit muddy. Main reason is that yes you have a chunk of the pie (medical reports), but most times its difficult to assess how much is missing (KIA) via what weaponry, in order to reasonably make a good calculated overall guess. Sometimes you can figure out a feasible guess but knowing that it will have an inherited range of error nonetheless. Worse part of it is that what was the most lethal, is the part thats normally missing.

Ive used information on excavated dropped & fired rounds in a given battle area to try to determine the general position of a given unit. What was found dropped... what was found fired around their immediate area from the opposition. Ord records of who was armed with what, at least prior to the engagement, to make a reasonable guess at it. Was looking to try to find the inital battleline position, which was a Mass regiment. They were known to have been armed with Enfields. Found dropped enfields, enfield rifle parts, eagle buttons, in a specific line. All in front of and around it fired 58 CS 3-ringers, and gardners. Which told me a given Virginia brigade was most likey their inital contact. An Alabama brigade on the flank was armed mostly with 69 calibers. None of those found where the Mass unit was dug in. However many times it isnt quite that clear, and you find a hodge-podge of mixed rounds in and around a given spot, as battle lines tend to shift and move along, and multiple units tread across a piece of same ground before its over. Adding more confusion...lol..

Even this can be muddy since a given regiment might have several different types of weapons and calibers within its ranks at the same time. Same as the guys on their left and right. Most tried to standardize it for simplicity of ammo issues, but didnt always happen as good as desired.
A given troop position could have been cross fired on by different enemy units from different positions. Not always just the guys in their immediate front.

At Gettysburg itself there are many reports of units "upgrading" their weaponry in mass due to the many thousands of excess muskets laying about in short order after the fighting kicked in. What they had in their hands on July 3rd, might be different than what they carried on June 28th...
In the case at G'burg at the stone wall, there are accounts that after the fighting along that line on July 2nd, many of the federals gathered up hoards of extra muskets, many picked up from the enemy. They put these in mass leaning and loaded against the wall. In some cases reported that individual soldiers had as many as seven muskets at the ready before him. Since they were stationary, and if the Confederates made another dash across that field they could deliver a steady fire without the need to pause for reloading at least for a couple good rapid volleys. What was fired across that field in the inital opening rounds on July 3rd as the Confederates reached the fence, was most likely a wide range of mixed rounds and calibers.

What your doing is interesting and fun to do. One tends to uncover many lessor or unknown items about a unit or engagement along the course of the research. Which if like me uncovers other mysteries and ponderings that spawn other research treks. An endless circle...lol.. Certainly not implied as a waste of time by no means. Just sharing my prior research and experiences with same for general reference. Can be frustrating at times when one places so much effort into something when it at best might only end up with a 60 or 70 percent accuracy level on a good day. If one is aware of the potential varibles that exist, and taken into consideration along the way as you dig further.

Respects
Frederick

PS: Tom are you in the Richmond area?