Thanks! You're right, one should always give the specs on these. It's 6.65g and 26.5mm, RIC 231, issued late summer 307, just before his (re)-elevation as Augustus. Here are some snippets from RIC describing successive weight changes at the western mints. Cloke & Toone give a much more detailed account of the London changes in their book.
RIC VI, 66 CT 4.04.009. Constantine as Caesar, struck at the London mint. A large, un-reduced coins with no mintmark on the reverse. Probably from the very first issue of coins in his name. These are, I think, very scarce in Constantine's name. It is a tad bit rough. One of my favorites!
Great coin!! Jealous. (Note that you can insert the image anywhere into your post by clicking on the "Full image" button after you've uploaded the file. It's placed wherever your text cursor is. Most of us prefer to have the image right in the post like that... if you edit your post, you can even do this now.)