That's a very nice collection of finds! The buckle is really interesting. I can't help you with a rough date, but I'm sure someone else with chime in. Congratulations.
Some people will try & tell you, you have a rare 18th C batwing buckle from the Rev War. It's not, both the buckles you have found are circa mid-19th C horse harness buckles, somewhat back up by the fact that you have found 2 different types of the same function & period (in the same general area, I assume).