It's important to report a few relevant historical facts on the subject of this so-called "8-pounder ball."
In the following report, I use the term "gun" because it was the civil war artilleryman's term for a long-barreled Smoothbore cannon... for example, the Napoleon 12-pounder Gun. Terms for the shorter-barreled Smoothbore cannons were the Howitzer and the Mortar.
1- The 8-Pounder Gun was a French smoothbore cannon, from the Colonial Era. The British and Americans had no equivalent for it.
2- As some of you already know, the "Pounder" designation for a cannon is based on the weight of a Solid-Shot projectile for that cannon. However, in the case of the 8-pounder gun, its Solid-Shot did NOT weigh eight British/American "Avoirdupois" pounds... it weighed eight French pounds. (I can't recall the French pound's exact name... I think it was the "livre.") The French pound-weight was slightly heavier (1.097 pound) than our US/Brit Avoirdupois pound.
See the "DeValliere System," here:
https://en.wikipedia.org/wiki/Florent-Jean_de_Valli%C3%A8re So, France's 8-pounder Solid-Shot weighed about 8 pounds 13 ounces, just slightly less than a British/American 9-pounder Solid-Shot. An 8-pounder cannonball was about 4.05-inches in diameter, and the US/Brit 9-pounder ball was 4.10-inches. The British army was delighted to discover that captured French 8-pounder cannonballs fit very nicely into Brit 9-pounder guns.
An additional heads-up, for RevWar cannonball collectors:
The American/British 12-pounder gun's bore diameter was 4.62-inches.
The French 12-pounder gun's bore diameter was 4.76-inches (121mm).
3- In four decades of civil war artillery study, I've never seen a report of an 8-pounder gun being used in the American civil war. But, if one was used at Shiloh, its projectiles could be identified by being just .05-inch (1/20th-inch) smaller in diameter than Brit/US 9-pounder cannonballs (4.10-inches, according to the US 1861 Ordnance Manual's Shot Tables at:
www.civilwarartillery.com/shottables.htm.
And as I indicated above, the 8-pounder gun's Solid-Shot weighed about 8.8-to-8.9 American pounds.
4- According to the Shot Tables, there is no Grapeshot ball or Canister ball which is anywhere close to 8 or 9 pounds / 3.65-to-4.0-inches. Any Solid iron ball in that weight/size range is not an artillery ball... but instead, most likely is a rock-crusher/ore-crusher ball.
Speedenforcer, I second Relicrunner's suggestion... those Shiloh balls' precisely-measured diameter and very-exact weight (pounds & ounces) will tell us what they are, or aren't.
After-posting edit:
I modified the previous version of the text above to include the precise diameter of an actual 8-pounder cannonball, which necessitated some modification of the text.
Regards,
Pete