They are both percussion guns and both flint and cap locks have vents.
Well not exactly, definitely not in the same sense.
A cap lock ignites from the hammer hitting a cap containing percussion powder. It thus ignites from the percussion.
A Flint lock does not ignite the powder from percussion. It strikes a spark of red hot steel which ignites the priming powder.
Some cap locks were drilled with vents, others were not. The onky "Vent" any of my cap locks have is through the nipple. As the hammer stays down on the fired cap, which is not blown off, there is little if any escape here.
