Additional info about the civil war Gardiner Explosive bullet you dug:
It was invented by Samuel Gardiner of New York, and he received US Patent #40,468 for his invention on November 23, 1863. (Strangely, the Patent wasn't issued until nearly a year after the US Army began issuing his explosive bullets to troops.) Unlike the typical lead civil war bullets we dig, the Gardiner Explosive bullets we dig always have a darker color, because they were made of pewter or a "hardened-lead" alloy, which doesn't form the white-ish oxide/patina that lead does.
You can view Samuel Gardiner's US Patent (with diagram and explanation) here:
http://www.pat2pdf.org/patents/pat40468.pdf
If that link doesn't work, go here and type the patent-number (40468) into the search-box:
PAT2PDF - Free PDF copies of patents: Download and print!
In my previous reply-post, I told you its value was $100+. I did some websearching for you, and found a dug Gardiner Explosive bullet listed on several civil war bullet dealers' website. Their ASKING-prices range from $145 to $190.
Lastly... I should mention, be sure to notice that Samuel Gardiner's name has an "i" in it. That is important because there is a Confederate NON-EXPLOSIVE bullet whose name is very similar... a Gardner bullet, which doesn't have an "i" in the name. So, if you do a websearch for other examples of your bullet, be sure to include the "i" in its name.