Lighter 38 bullets shoot lower or higher?

[halfmoonclip]

Wrong handed, I'm with you 'till the gas exiting the barrel making any difference; blanks have negligible recoil, and a narrow air jet is a different critter.
If we put a straight edge across the sights of a revolver, you'll see that the barrel bore and line of sight diverge; the bore is actually aligned somewhat below the target until the shot breaks; the bullet exits as the gun rolls up in recoil.
This is the basis of internal ballistics; the long, looping arc of a bullet's flight path is external ballistics, and that is a whole different thing. A slower moving bullet will hit low at greater ranges.
Moon

 

[JohnKSa]

So recoil is not an effect of the bullet exiting the muzzle but leaving the casing and entering the bore??

Recoil is due to motion. If the bullet moves in one direction then the gun must move in the other direction. That means as soon as the bullet starts to move, so does the gun. If you want to know the total amount of recoil, then you only have to look at the numbers in terms of what comes out of the muzzle. If you want to know what's going on while the bullet is in the bore, you have to consider that the gun starts moving at the same time as the bullet.

As the bullet leaves the barrel, so do all the gases that created the pressure to force the bullet from the barrel. This also causes recoil.

That is correct, however the recoil caused by exiting gases does not affect point of impact of the bullet since the gases exit after the bullet is out of the barrel. It also tends to have a much smaller effect on recoil than the bullet since the bullet is so much heavier than the gases.

The overall effect on the gun is due to the momentum of the ejecta which is everything that comes out of the muzzle, not just the bullet. The effect on the point of impact is due only to the effects that occur while the bullet is still in the barrel--due to the movement of the bullet.

Technically there's some recoil caused by the gases moving down the bore behind the bullet before the bullet exits, but that is a very small effect since the gases weigh so much less than the bullet and are moving at the same speed as the bullet. Once the bullet exits the muzzle, the gases are no longer constrained and at that point they exit the muzzle behind the bullet at very high velocities--overtaking the bullet.

For example, let's say that the load is 4grs of powder behind a 124gr bullet with a muzzle velocity of 1100fps. If we break down the individual effects, it looks like this:

Bullet momentum is 93-94 % of the total momentum.
Gas momentum (movement of the gas in the bore before bullet exit) is 1-2% of the total momentum.
Jet Effect momentum (exit of the gas from the muzzle after the bullet exits) is 5-6% of the total momentum.