It looks like No. 4 is a cap lock. (looks like)In the following link, go to the second photo of a group of locks. Look carefully at number "(3.) A flat British export pattern having a distinctive right angle in the lockplate forward of the frizzen and a panoply of arms engraved on its tail (c. 1730-1760)." Notice the hole through the Top Jaw Screw?
Hunting Guns in Colonial America (ladybemused.com)