I was at the range today sighting in an upper
that I put together out of spare parts . It's
nothing special , but it does have a match grade
SS bull barrel 1-8 twist and was sub MOA in its last
configuration .

Anyway it was drizzling when I got there so I
didn’t want to set out paper targets . Instead I
tossed a dozen clays on the berm which is 125 yds
from the shoot house .

It only took a few rounds to get the glass zeroed
in using Black Hills 68 gr HP heavy match . Then I proceeded
to pick off the reaming clays . With the next 20 rd mag
I was picking off the bigger remaining pieces when it started to rain
harder . As soon as the rain got heavy I noticed that
the bullets were now hitting 2-3" lower then the POI I
was getting before it started raining hard .

Now here is the curious part . I switched to 62 gr 855
FMJ and the POI returned to where it was .  I thought
Hmmmm Odd . So I switched back to the 68 gr HP's and
the POI dropped again .... WTF .

To test my conclusion I loaded up a mag with alternating
62 gr FMJ and the 68 gr HP's in groups of 5 . Sure enough
the 62's shot to scoped zero and the 68's were 2-3" low
BUT only when it was raining moderately , when the rain
slowed they both shot MOA to each other ???

I have my theory , but I'm interested in what others
think would cause this variance .

So whatta ya think ??  

I shoot a 100 yard prone rimfire match tuesday afternoons.
We had set out targets,and set ourselves up under a covered fireing position when the sky opened and the hardest rain you could imagine began to fall . Target rimfire ammo is less than 1100 fps when it starts so time to the target is about 1/3 of a second. Thru high power target scopes you can see the bullet in most light conditions from 50 yd on out to the target . Wind usually knocks the bullet around some but in this horrible rain condition (with little wind ) the bullets were flying true and straight. Logic would seem to indicate some raindrop strikes but actual experience indicates otherwise . I must argue that a .223 with bullet speed 3 times faster (flight time 1/9 second at 100 yd ) has an much less chance of strikeing a raindrop .
Three of us were shooting that day and it is a 40 shot match. We had a difficult time seeing the target but none of us could  claim a bullet diffectled by a raindrop.

I would think that it has more to do with the density of the air/humidity = more resistance than anything else.  Less mass will lose less velocity and drop more than a bullet with more mass.  At least I was taught in bootcamp that the chances of a bullet hitting a raindrop are very slim to none.  That makes sence to me, but I'm not an expert by any means!

Quoted: Logic would seem to indicate some raindrop strikes but actual experience indicates otherwise . I must argue that a .223 with bullet speed 3 times faster (flight time 1/9 second at 100 yd ) has an much less chance of strikeing a raindrop .

The bullets were unquestionably hitting rain drops since it was coming down
pretty good . I had to back the scope down to 4x to see the
pieces on the berm , at higher magnification all you could see
was the rain .

The thing is . It was only effecting the 68gr bullets .

I remember reading something on this subject awhile back.  The just of the artical was that the bullet was traveling so fast that it would cause a type of drag or cusion around the bullet that the rain drops would just go around.

Just think if it as a car going down the interstate.  Yes it is getting wet but the faster you go, it seems like the rain just doesn;t make contact with the car as much.  Maybe this doesn;t make much sence as I sometimes don;t explain things well but that is my understanding.

I would think that something else was at work here.  

Well , here is my unscientific theory .

The more I thought about it . The only thing that
made sense is that the HP's were opening up
from the hydraulic pressure of the water as the
bullet struck the raindrops . The increased aero
friction slowed the rounds down enough for gravity
to pull bullets down 2-3" due to the longer flight
time .

If it were just the slowing effect of striking the drops
then it would have effected the FMJ to the same
amount , which it didn't .

So there it is , feel free to tear it apart

my theory is that since the 68gr bullet is longer than the 62gr so hence is takes more beating effect from the rain.  example would be a car going 60mph on the highway and a bus going the same speed.  the bus would be exposed to more rain because of it's surface area compared to the car or in this case, the chances of the 68gr otm bullets touching water is much higher than the standard 62gr round.

If you fellas are interested I can dig up an older article in Precsion Shooting that explored this subject. If I remember correctly, their findings were that rain drops did in fact penetrate the shock wave and flatten the nose of the bullet.

Can it be that the raindrops are affecting your line of sight?  Just like putting a stick into water.  Just a thought...

Quoted: I would think that it has more to do with the density of the air/humidity = more resistance than anything else.  Less mass will lose less velocity and drop more than a bullet with more mass.  At least I was taught in bootcamp that the chances of a bullet hitting a raindrop are very slim to none.  That makes sence to me,

1. Humid air is less dense than dry air.  (Look it up)

2. Less velocity loss = LESS drop,  not more.  (Think about it).

but I'm not an expert by any means!

Don't mean to be rude, but you're batting .000 here.  Perhaps you should limit the posting for awhile.