Because you asked for ID and time-dating of your buckles:
1- The brass "oval frame" buckle is from anytime in the entire 1800s through the early-1900s, and is Civilian, not Military.
2- The rectangular brass buckle with a "backset" center-bar is from the mid-1800s through early-1900s. Those are "utilitarian" strap-buckles, meaning they are so broadly useful, they were utilized by both the Military and the civvies. I've seen that same form of brass buckle on civil war cavalry carbine "saddle-thimbles," and on civil war through World War One US Army McClellan saddles, but ALSO on civilian saddles and other horse-harness straps. That means there's no way to time-date with absolute certainty -- unless it was dug a foot deep in a civil war trench or winter-hut.
3- A 20th Century civilian-usage strap-buckle.