Shooting over moving water...

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GuyBFF

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About the easiest place for me to find 500 - 1000m open areas where I live is over the river we have. Weird thing is, if I shoot on land 300m I get sub 1" groups with my Timberwolf. As soon as I go out to 5 or 600m, groups are opening up drastically .. about 8".

On the days I've shot lately, there's been almost no wind, but I'm starting to wonder if the river / water turbulence is creating it's own weird wind, I can't feel it in the boat, but it's the only thing that can explain the extreme group differences.

Any thoughts?
 
Might be a bug hatch. I've also noticed while fishing, that the constant horizonal movement doves weird things to the eyes. Alders bow in the middle in the direction of the current.
 
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"...300m I get sub 1" groups..." Are you saying you're getting sub inch groups at 300 meters? If you are, you should be in the Olympics.
 
Right now, I'm mainly trying to get my dopes figured out with the new stick. I can shoot 1" groups at 300, but I think the guys and gals in the Olympics aren't using a Bipod and Bag, I know I can't shoot anything near these groups otherwise.
 
I can't say I'm a ballistics expert,but I know something that might explain your observations. Have you heard of "Convective turbulence"?

You see...I helped my dad get his private pilots licence by making study tapes for him and I learned a few interesting things.

Different surfaces absorb, release and radiate heat very differently, providing lift or downdrafts.

For example, hot tarmac on a sunny day gives great lift, which can be a problem while landing. An aircraft going from vegetation to the beginning of a blacktop runway, can suddenly gain ten or twenty feet of altitude in a second, and it can screw up a landing causing overshoot, or if the pilot overcompensates, or foolishly tries to make the landing anyway...can result in a crash.

Conversely, if you are flying low over a large parking lot, or sandy area, you have artificial lift, which can disappear when you reach vegetated area, or turn into negative lift over a body of water, plunging the plane into powerlines or other obstacles that you thought you had enough altitude to avoid.

These problems can be magnified if you are in a bank (turning) while making transitions from one land type to another because of reduced lift and altitude control while banking.

Could these "Convective turbulence" effects perhaps start to explain your observed loss of accuracy? perhaps it isn't the moving water itself, but the transitions from hot/cold/hot air, that are disturbing the flight stability of your bullet.

I mean...if a hot road, or a cool pond can make an aircraft weighing several thousand pounds drop ten feet in a single second...perhaps one or more of those transitions can seriously affect accuracy, by a few inches or more?

currents.gif
 
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Moving water creates it's own wind, it's not always strong and often shifts directions due to waves, eddies, etc... Depending on the conditions such as other winds, sun, heat, humidity, and so on the moving water winds will be at different height levels, velocities and directions too.

Makes for interesting shooting conditions...

Troutseeker
 
Luckily .... the lakes are frozen now :) .... everywhere I look is a 1-1.5km range ... hoorah.

Going to play more with the theory that the water has lift by shooting in different conditions in the summer (sunny/warm vs. overcase/cool) to see if that could be the issue.

Thanks guys!
 
I dunno about the rifle he has but I get 0.5" at 100 meters with stock Savage 111 in 30-06.
Oh, the scope is Nikon ProStuff 3-9x40 BDC.
 
Not too sure about shooting over water having an effect on a bullet. How does the rifle/load group over land at 500-600 yards?
 
Humidity will be much higher over the water so the air will be more dense. A 1-2moa drop could result. temperature will drop too. Try run the differences through a ballistics program. The air movement over water would also have a play at the end result depending on how close to the water level your shooting. This would make for a great test to see what the effects are.
 
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Catnthhatt and I set up measured 1000m and 1 mile ranges diagonally across the Athabasca River a few years ago. Groups did vary some, but were around 8-10" at 1000m (bench/bipod/bag) with 6.5 WSM, and I did get one half decent group 11" with my TRG-S in 338 Lapua from the monkey humping a log position.(okay, so the .338 group was only a 3 shotter).

I think Maynard has the right of it when he asks how your groups are at these ranges "dry"! Once you get out there, the wind has much longer to deflect bullets and its a whole different game.
 
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