Would it ever hit it? Pressure in front of the bullet should push it out of the way, correct?
Correct. Based on reports from competitors, every now and again you can get a bullet to hit a rain drop (probably a really large drop, at that) that throws off the POI by a bit, but it's a very rare thing.
The pressure wave in front of the bullet, combined with the short TOF, both favour the likelihood that the bullet never touches a drop of water when you go shooting in the rain.
If the pressure wave pushed the rain drop out of the way, Sir Isaac says that the reaction on the bullet has to be equal and opposite the reaction of the rain. That a bullet moves in the wind whose air molecules are proportionately so much less massive says the bullet will move. Because center mass of the rain drop may be randomly distributed around the axis of the bullet means the deflection may be random. Whether or not the bullet's pressure wave moves the rain drop or the rain drop does indeed hit the bullet is not relevant. A bullet fired n the rain may deflect less than a bullet fired into grass or brush, but it will deflect in the same manner with the same random dispersion.
Having found a fair number of Barnes bullets butt first embedded into trees behind my targets I suspect that a very small upset is possible and may cause them to tumble and restabilize going backwards because of the drag of the upset. I doubt the stability is very good. Of the bullets found embedded, it looked like maybe 80% went in butt first. It might well be that this sample is not representative. It may be that only Barnes TSXs are prone to doing this. It might be that only a specific kind of upset triggered by very specific conditions can cause this.
The chances of a bullet fired at a deer hitting a large raindrop and deflecting enough to matter are remote. Deer are not usually out in the open presenting longer range shots in rain that has big heavy drops. Light mist, light drizzle with small drops and snow, yes. BTDT. Never seen or heard of a deflection.
