Okay Michael, Wes, Terry, Mike, Jim, R.J. and all. I've resisted staying out of this one simply to avoid the lashing that will undoubtedly ensue. Please be as gentle as possible.
Back in the 1980's I was fortunate enough to dig several of these from two small cavalry camps at Crystal Hill (AR) one of which is featured in Tom Stelma's book. One of the most noticable features of these bullets is that all seemed to be "out of round" to some degree or another.
The way I was taught to measure the diameter of a bullet was to take several different measurements and then take the average. The bullet in Tom's book measured anywhere from .519 to .541 hence an average of .530. The skirts on these bullets are very thin so they are easily distorted. Taking just one measurement in such cases will not neccessarily give you the true dimension of the bullet. I believe they are all .54 caliber.
Now for the beating. I think that this particular projectile was cast in a modified .54 caliber Gardner mold at the Arkadelphia Arsenal. The mold would have been cut off at the base so there would be no excess to crimp. This would explain the shorter base than on a Gardner and the thin skirt. The bullets are of the same shape, they have the same number and type of grooves and both are nosecast... OR the bullet could have been cast and they figured some way to cut off the bottom part that would have been crimped but doing this without deforming the skirt would have been a difficult task.
Granted this is just a theory and there is no written documentation that I know of but it does make sense.
Now for the whipping...