Virginiaguy, please pardon the delay in replying... due to relentless Insomnia, I haven't logged on to TreasureNet recently. Your finds are very interesting. I've never seen anything like them which is that size. What I have seen is, much larger (4.62"-caliber) FIRED canister top-plates with ball indentions caused by firing blast. My thoughts:
(1) As specified above, the indentions in the 12-Pounder caliber canister plates were caused by firing-blast. Your post didn't say whether you found the plates and balls "scattered" from firing, or in a close group from deteriorated unfired canister ammo. If you did find them in an unfired grouping, the indentions in the sheet-iron disc were manufactured that way... and in my 40+ years of closely examining civil war artillery ammo, I've never seen any like that.
(2) As you may already know, the method we artillery projectile collectors use to determine (with certainty) whether or not an unidentified object is an artillery projectile or not is to do super-precise measuring of the object's diameter, and then see whether its size matches up properly with the bore-diameter of any known cannon. If there is no match-up, the object is not an artillery projectile. You say the plate's diameter is about 1.75-inch. That size doesn't match up with any cannon's canister ammo used in the civil war.
All of that being said... your find sure does closely resemble canister-ammo components. Please tell us whether you found them as an unfired group, or "scattered" from firing.
Also, since you live in Virginia... if possible, please bring them to the big civil war show in Richmond on July 21 & 22. I'll be there (at my sales-table), along with several other very-advance civil war artillery projectile collectors. Perhaps some of those other oldtimers have seen something like your find.
