Hard rain and POI?

[BANG...ping]

OK, so today I am at the range punishing the little black dots at 100 yards. After 5 groups of 5 my elevation and windage is on or very close to a 5/8th inch target. Then it starts to rain hard (not much wind). My next group is fantastic (about.5), but evevation on all shots is about 9/16" high. Still a great group (slight horizontal string) but all shots high. So I go sit in my car and after about 15 minutes the rain stops and I resume shooting. My next group is the best of the day with all 5 rounds completely inside a 5/8 inch dot. I then shot 4 more groups of 5 with elevation and windage dead on (all groups .7 or better). I did not touch the zoom ring, parallax setting, or elevation knob, and all ammo is factory Hornaday 140 ELD Match from the same lot. All shots prone at a slow pace, barrel was warm but not hot. I checked later on and nothing is loose. My rig is RPR 6.5, Nightforce 5-25 F1, Nightforce rings, Harris bipod, about 1200 rounds on the great factory barrel. Is this normal? I am starting to shoot PRS matches and am sure at some point I will be shooting in the rain so I am trying to get a feel for this. I know 9/16 is not much, but this is only 100 yards. I have the gun for about a year and it alwas holds zero. Any input?

Thanks,
Bang

 

[Griz44Mag]

EVERYTHING has an effect on the flight path. Distance, direction of travel, temperature, humidity, barometric pressure, barrel temp, powder temp. etc.....
At 100 yards these effects are minimal, but they do exist. Rain can cause very erratic behavior. But dang, it's fun shooting in the elements!
Download an app called BALLISTICSARC. It's free for the basic functions, but the 12 bucks for the registered version opens a lot of doors that will answer a lot of the questions you just asked.
I consider it a must for hunting and shooting long range matches.

 

[morganlamprecht]

i dont change anything for the rain, especially at 100 yds, no problems hitting everything so far...its likely the effects of the rain were affecting you in some way not obvious (if youre actually uncovered shooting in it, or the degraded scope image if looking thru hard rain fall, etc)

 

[MarinePMI]

I'd add that the rain itself isn't probably affecting you, but rather the associated change in temperature and barometric pressure. I'm pretty sure Frank put up an article/video on this very subject not too long ago...

Intermittent rain/squalls is where a Kestrel is worth its weight in gold (IMHO)...

 

[TheOE800]

Just this weekend I shot through a rain storm. Dope before the storm and during were about 300DA apart, I suspect largely due to the pressure change.

 

[morganlamprecht]

DA changes...@ 100 yds...well, alright then...

 

[TheOE800]

DA changes...@ 100 yds...well, alright then...

Well, I was shooting 800...but DA changes at 100yds should be imperceptible. Change in POI will be smaller than the bullet hole at that distance.

 

[morganlamprecht]

Well, I was shooting 800...but DA changes at 100yds should be imperceptible. Change in POI will be smaller than the bullet hole at that distance.

exactly, 800 is one thing, but the OP is at 100 yds and already has 3 replies about atmospheric changes...trying to keep him out of the rabbit hole he's being shoved into

 

[TheOE800]

Likely a positional issue then. I've had groups vary by more than a half inch from POA based on my position being wonky.

 

[PRDRIVER]

Is your ammo getting wet before you load it into the rifle. I got stuck shooting some horrible weather matches a few years back. There was nowhere to hide from the rain. I found that my rifle had a POI shift when shooting ammo with water on it. Increased pressure signs were obvious as well.

 

[Lowlight]

If the ammo got wet at all there is the problem.

The shock wave of the bullet moves any rain drops out of the way so they really never hit the bullet. In short, they vaporize the rain.



Rain tends to bother us first, and the bullet last, especially at 100 yards.

But a wet bullet in the rifles chamber will increase the pressure and cause a shift. Water does not compress, so you can see it increase velocity, pop primers, and even break triggers.

 

[MarinePMI]

DA changes...@ 100 yds...well, alright then...

Well crap. I missed the 100yd data point...

 

[Rob01]

Rain, heavy or not, will not effect POI. It will effect the shooter. I have shot matches in heavy rain and didnt change any data especially at 100 yards.

 

[BANG...ping]

Thanks Low for the input. I always try to keep my ammo dry, but now that I think back, the ammo may have been wet. Like I said about my barrel being warm. I load 5, shoot my group, remove the mag, load it and then wait for the heat to dissipate from the barrel while the mag sits on the bench (there is no roof over my shooting point). It had just started to rain hard when I began my group. I would never put a dripping mag in the gun, but it may have been a bit wet as it started to rain. I just don't remember. It was just weird that it was such a tight group, but high. I know I didn't yank the trigger the same way 5 times. All of my shots felt good. All of my groups before and after the rain were good. It is likely that a higher pressure may have accounted for the temporary elevated POI. Real world testing pays.

Thanks to all for the responses,
Bang

 

[TheOE800]

You owe it to us to go out, pour some water on your mag and let us know what happens. ;-)

 

[jakelly]

Water in the barrel can change things, too. Doesn't sound like the case here, but just FYI.