Fullstock's deduction (he said "looks like") is correct. Both objects are broken pieces of the same brass stirrup. The curved-frame strap attachment at the top is a distinctive feature. Here's one on a US Army Model-1833 Dragoon strirrup. That feature suggests yours is also from the early-1800s. That being said... I haven't seen a Military stirrup with the decorative seashell shaped arm yours has. And THAT being said... I do not believe I've seen everything.
Thanks TheCannonballGuy. I can offer that the cart path up the side of this hill has a property marker just beyond the end of the path. I went back yesterday afternoon and recovered another target from the path, a portion of a horseshoe, which was down about 18 inches. The stirrup pieces were deep as well. The property marker I mention is now the third I've found associated with this old estate that was purchased from Charles Ridgely of Baltimore County by Robert Gilmor. Gimor's estate consituted about 1000 acres. The Gilmor home was built in the 1830s.