This assumption is based on the condition of the gun when the ammo exits the barrel. At ammo exit, the average velocity of the gases is basically 1/2 the muzzle velocity. Why? Because the gases directly behind the ammo can not be moving any faster than the ammo. The gases at the breech end of the gun are not moving at all. Neglecting things like friction, temperature gradients etc., the velocity of the gases is linear with the distance from the breech (for a gun of constant chamber/barrel diameter like a real rifle). Since velocity is linear with distance then the average velocity of the gases at ammo exiting the barrel is half the muzzle velocity.THUNDERLORD wrote:Also you state to "assume the air is moving half velocity of projectiles" the gas propelling the projectile is moving faster in some cases and actualy overtakes the projectiles in some slow speed photos so you are the one who's wrong again.
For a momentum calculation all you need is the average velocity of the object. Very basic physics and probably more than accurate enough for most spudguns.
1) Einstien plagarized things he saw in a patent applications for his various theories? Care to find the patents the he copied from? Having an opinion on something is one thing, pulling stuff like "he plagarized" out'a your ass is just a sign of ignorance.
2) Einstien was not an average student by any stretch of the imagination. He published his first paper before he entered college. How many scientific paper did you publish while in High School?