Thanks Carl. You know, this is an older picture of the base, and the ruler is not placed very well. I'll have to, at some point, go dig the thing out of my boxes of relics to check, but I'm thinking it will measure to 3.67, but that's just a guess, since 6-pdrs were there (I've edited my previous posts while you posted, mentioning this fact).
To your "wood" part in regards to the sleeve: Don't know, but it was found in a plowed field. To be honest, I thought it reminded me of two things: 1) charcoal 2) the rubber or leather gasket in a sectioned 12 pounder I have. To RipCon, he felt it resembled very old, dried rubber. As to me hitting it a lot with my shovel -- LOL. Plows hit it over the years!!! That's my story and I'm sticking to IT!!!! Thanks!!!