Go to the Google advanced search page. On the first line type in "civil war artillery", on the second line "grease bucket", and on the third line "image. Several sites will pop up that show period grease buckets up for auction. Grease and water buckets were usually straight walled and very heavy construction. And all I've ever seen had a lid as the ones in the photos will show. Grease buckets had one side of the lid pinned to the top so it slid to one side to access the contents. A lot of water buckets I've seen have a lid attached with a chain and can either hang outside of the bucket or drop into the water. In the water is how we usually use ours. There are two ears on each side of the lid that line up with cutouts in the bucket top that allows the lid to fall into the bucket. This feature also eliminates the possibility of losing the top. Your bucket looks of period construction but not like artillery. Just my opinion.

Keith