If you want an easy target for open sights, go to Wal Mart and get some of the bold colored 3"x 5" index cards. You draw a X from corner to corner, tape that to a box and then shoot for the center of the card.

This card was the first time I ever shot my flintlock a .54 caliber Lyman Trade Rifle. I wanted to see where it was hitting and this was a good indication of what I could expect.. They make an excellent target and easy to see.. Keep your shots on a card and a deer has no chance.