Your bullet is a 4.7 inch Gun Model of 1906 or Howitzer Model of 1913 shrapnel projectile of WWI vintage. It is very characteristic of shape and the groove at the base of the projectile and the fuzewell details are the key identifiers. I have attached some photos of a sectioned projectile like yours next to a slightly different variation. Most of the 4.7 inch U.S. projectiles (there are 4 types, Gas, Nose fuzed HE, Base fuzed AP-HE, and shrapnel) have bases with just two crimping grooves like the black projectile. But for some reason there is a variation of the shrapnel that has the big groove like yours. I have the sectioned example and a fired one like yours.
As you can see in the sectioned projo, these are filled with lead balls for shrapnel, that sit on top of more than a pound of black powder and a pusher plate. A filled projectile weights close to 50 Lbs.
The fuze used in these is the Model of 1914-15. These are fired from a straight brass case. Complete rounds look like ovrsized 105 Howitzer rounds. By the numbers, the gun was invented and began use before the fuze that is shown was developed. This is one of the few U.S. designed artillery pieces that was used in WWI. We used a lot of French ordnance in WWI due to lack of preparation on America's part.
Lastly, no need to appologize. You did everything right: You posted good in-focus photos with measurements.
