Different density than air!!! The straight head-on collision impact would create a sudden drag, slowing the bullet's V a little!! 1) Drag changed the bullet velocity!!
Not only did the different momentums in the head on collision slow the bullet, it also caused more friction in the rotational surface cause a change in the rotational inertia!! That little sudden change caused torque which opposed that fictional force!! That torque would tip the bullet's rotational axis!!
2)The frictional force of the water on the bullets surface would tip the bullets CL axis!!
That rain drop is falling straight down for this scenario!! That droplet has inertia (momentum) and is at 29 f/s (terminal velocity) downward (Vector pointing down)!! That droplet vector will shove the bullet down!!! Think sectional density!!!
3) Collision downward would push the bullet flight path downward!!!
The total effect of the bullet/raindrop collision would be the vector sums of 1)-3)!!!!
In reality, not knowing bullet RPM before the collision, V at the time of collision, mass of the bullet, SD (Sectional Density), droplet mass or volume, I'm going to make an educated guess!!! It would be like a Semi hitting a dear!!!! If that collision occurred within the 1st hundred yards, it would, not could, open impact at long range!!!
I'm going to tackle this problem with brut force physics and math just to get a rough idea of what is happening and it will be close, but not exact!!! We have the perfect rain droplet falling straight down and having a VECTOR at 180°, or 3), and a bullet traveling perfectly horizontal having a VECTOR at 90°, ie 1)!! Using a 2 body collision model (Conservation of Momentum), the trig results are around 0.075 MOA bullet deflection with a 150gr bullet traveling 2500f/s and medium or average droplet size of 3.5mm diameter at 29f/s (Term V)!!! Now the big droplet of 7mm diameter (hail soon to follow if more heat is sucked into the cell) would deflect that bullet 0.75 MOA!! Hit 10 of those bad boys and it could deflect more than 7.5 MOA!! Why are we out shooting in this shit??? In snow, mist, light rain with small droplets, just chance the humidity and temperature settings in your ballistic calculators!!
Keep in mind, you have to establish where the collusion occurred and know the remaining distance of flight to the target in order to calculate how much deflection will occur on the target!! Adjustments in velocity lost at collision must be used to finish the remaining distance to the target!!! Medium droplet at the muzzle and target range of 100yd would deflect 0.075"!! If collusion occurred at 50yd, deflect would be 0.035". 75yd, 0.018"!! 1 foot from target, assume 0 deflection!!! Just multiple by 10 for 1000yd!!! These figures are within 10% scientific error (probability, not statistical)!!!
BILL
AIM SMALL, HIT BIG!!!!