Great pin, congrats. It appears nearly identical to my Great Grandfather's US Army Spanish American War hat pins, 1898-1902. I am sure militaria experts will fully advise shortly. You had a great hunt! Sub
During the civil war, the Infantry insignia was a hunting-horn. In 1875 the horn was replaced by crossed flintlock muskets -- which is still the US Army Infantry insignia today.
The Company-letter and/or Regimental-number were not physically part of a hat or collar insignia during the civil war, and not until 30 years later. That construction began in 1895, and continues today. Your US Army Infantry insignia appears to have a pin-&-clasp attachment form on its back. That dates it from 1895 to 1905, because the flintlocks were changed to breechloading rifles in 1905. (The rifles were changed back to flintlocks in 1923.) From 1923 until World War 2, the attachment form was a screw-pin. During WW2 and up to today, various forms of clutch-pins have been the standard.
Thank CannonBall. Hey I kinda work part-time for Nicky Harris he told me little bit about you and that you really know you're stuff and he says get your butt up to his shop and look @ more of his Virginia Buckles