I have some time this morning, so I could muse a bit..
here is what I got to say, mind you I might be wrong..
==== case 1 ===========================================
==== assuming the rain does hit the bullet ========================
Here some assumption are taken :
- the projectile is a cylinder with straight wall from meplat to heel
- the bullet flight duration is 1 second
Rainfall is measured by a gauge which have a funnel to catch rain and a measuring cup under the funnel.
The measuring cup surface area is usually exactly 1/10 of the funnel catchment area,
and the measuring standard should be height of catched rain / hour.
Statistically anything below 2.5mm (0.1 inch) of rain is classified as light rain,
2.5 - 7.5mm (0.1 - 0.3 inc is moderate rain
and higher than 7.5mm (0.3 inch) is heavy rain.
Ok, having established the rainfall measurement, lets forward to the next step.
2.5mm / hour rain is 2.5mm / 3600 seconds or 0.000694mm / second .
A very heavy rainfall
of say 15mm/ hour, the rainfall is 0.00416 mm/ second.
Ok, now lets get a large and heavy .308 woodleigh of 200 grains length for our study case
The projectile length is about 25mm (1 inch) (I dont have one handy to measure, so I used what I have in memory - 25mm)
It is a good projectile to use for this study because it have a meplat area of about 0.270,
Or we could even say it is roughly a cylinder from meplat to heel.
So, we have a surface area of 7.62 x 25 mm = a bit less than 200 sqr mm projected from its side.
so if we take the standard rain gauge, the measuring cup should be 20 sqr mm cross section.
Ok, now the actual rain that will be catched by the projectile in 1 second would be 20 x 0.00416 = 0.0832 mm cube
with the weight of water at 1g / 1 mm cube, the weight of water that may hit the bullet in 1 second is 0.0832 gram
now with 1 gram is approx 15.4 grain, so 0.0832 x 15.4 = 1.28 grain
So by all the above lengthly calculation, I can deduce that the actual rain that may
hit the bullet in 1 second is 1.28 grain.
At my projectile weight of 200 grains, that represent 0.64% of the total weight.
I believe the tolerance of factory made projectile is about that..
so here I proof that there is NO difference in trajectory due to rainfall
==== case 2 ===========================================
==== assuming the rain does NOT hit the bullet =====================
Due to the high rpm of inflight rotation of the projectile, it would be covered by a laminar layer of air.
Thus will deflect any rainfall that may came close to the projectile.
Thus no difference in trajectory may occur.
==== case 3 ===========================================
==== Gelan need some beer ================================
This morning I donated 2 cases of my thoughts to you, now please donate at least a case of beer to the cause.
Seriously, you may get more effect from the wind that almost always accompany rains than the actual rain itself..
So here I rest my case