A small spherical projectile made of glass, about 1/4 inch in diameter, would be too influenced by wind to much to go, consistantly, the farthest.  On the opposite hand, a larger spherical projectile made of glass, say 6 inches in diameter, would not be affected by the wind, but may be too heavy and have too much mass to travel to far..  Say the pressure was 10 psi for all sizes of projectiles, what size would the projectile be for optimum distance?

I hope that the changes in the description and the question clarify some things.

a projectile dropped from a height and reaches the ground in  3 secs and the same body thrown with such a velocity that a body moves parallel to the ground for 3 secs. I  think the time will not be the same.