The vent is the hole in the side of the barrel, where the flash of powder from the pan ignites the charge inside the barrel. The heat & burning of the flash, sets off the barrel's charge.
On these old guns, the vent or hole in the side of the barrel is usually 1/8" in diameter.
Appears the pictures, with pan closed on the one above and the second gun it's only partially open, so no picture at an angle where the vent can be seen.
The newly made Indian guns, do not have vents, so are incapable of being fired, therefore they are not firearms as per shipping, mailing regulations.
I realize in the States, that black powder firearms are not firearms at all.
Same here with flint locks, as far a possession licensing goes.
Someone here who has a firearms ban, can own and shoot flintlock guns, cap locks, no.