Advanced Marksmanship POI Shifts From Different Surfaces

[ARobinson]

First Time poster here and fairly new member. I wanted to see what people have observed on POI shifts from different surfaces.

My set up
Prone
Bipod with Ski Feet & rear bag

Dirt/Grass - This zero has not moved in 5 months, Very slight changes from breaking down and rebuilding positions but only 1/10 mil from center

Wood Deck. - I was practicing a prone off of a wood deck and I noticed a POI shift about .3 mil high and .3 mil right (I checked at 100yds to eliminate environmental factors and observed the same POI shift, tight group high right) . Went back to dirt and zero was perfect, tight group in center.
Shot a match the following weekend. Prone stage was off the deck 500yd KYL rack hit to move on. First shot high right. Made correction 3/10 low and 3/10 left remembering the POI shift from practice. Impact 4x in a row on Know Your Limits Rack from 2 MOA to half MOA at 500yds. Wind was very slight, while i know that could be a contributor to the miss right at 500, my elevation was clearly off by 3/10. BIPOD legs were NOT loaded at any angles so i do not think there were any NPA issues.

Concrete - I have not tested this yet

Anyone else observe POI shifts high on hard surfaces?

Thank you for your advice.

 

[Diver160651]

If usually is NOT the surface but how you’re driving the gun.

Some people load really hard into the gun on shooting matts, grippy dirt and grass. Slippery surfaces does not allow the same kind of load. You’ll probably end up shooting high as well off of a barricade that does not allow you to load the same as you do on the grass.

 

[Lowlight]

 

[ARobinson]

Thank you for the reply. Ill try to match the rear pressure from my firing and support hand on both surfaces instead of loading the bipod into the ground next time out.

Thanks again,

 

[Bigwheels]

As a side question to this. What do you see when switching from a longer leg Bipod @ 45* to a shorter one at 90*? As in if I've been shooting an old short Atlas @ 90*. If I'm driving it right will I see a POI change going to the longer leg Atlas @ 45*?

 

[CharlieNC]

Perhaps ski feet are not the best for your shooting situations, they are designed to use for free recoil as in Fclass using the same surface every time.

 

[Diver160651]

I do not, but it is not a bad idea to grab a thick jacket, a bench, mat and on the raw dirt and run the gun in various positions, heights with thick and thin clothing as you selfspot..

You’ll notice some might be more comfortable than others or result in a large offset, these you can practice..

The offsets should not be large if you focus on making sure the parallax, cheek weld and load are similar.

 

[ARobinson]

If usually is NOT the surface but how you’re driving the gun.

Some people load really hard into the gun on shooting matts, grippy dirt and grass. Slippery surfaces does not allow the same kind of load. You’ll probably end up shooting high as well off of a barricade that does not allow you to load the same as you do on the grass.

Diver,
I was traveling for 3 weeks and didn't get a chance to practice and check my groups off a barricade. BUT...shot my club match this weekend for fun and to get back on the gun. They set up a barricade kneeling stage with 3 targets 3 shots each with wide short target (aka wind call)

SO..... Ran the stage and went 2/9 and the misses i could see were all high. Used a mulligan and ran it again BUT aimed at bottom of target and went 7/9....

100% correct, high impacts on barricades.

I have two full days training this weekend and will get this worked on.

Thank again for the reply

 

[ARobinson]

Perhaps ski feet are not the best for your shooting situations, they are designed to use for free recoil as in Fclass using the same surface every time.

Thanks for your reply, I guess ski feet is a bad description. Its a sako bipod, claw feet may be a better way to put it. They grip hard on grass.

 

[m1match]

I have a bad habit of loading the bipod heavily when I'm prone on a matt. The Atlas bipod and grippy rubber on my mat make it easy to do. I'm now making an effort to load minimally and my results in matches where we're prone, on barricades, and on tripods have gotten better.

 

[ARobinson]

I watched a lot of Franks training videos on how he loads Atlas vs Harris bipod. Also worked with Jacob at Rifles Only this weekend and got a nice tune up on my fundamentals.

Before this weekend I was leaning into the bipod with pressure, pulling the bipod into my shoulder pocket with both support hand and firing hand and impacting lower than other positions but getting excellent groups and used this for my zero.

This weekend I was just taking the slack out of my bipod and using the bottom three firing hand fingers for a snug pull into my shoulder pocket. I also worked on the floor grid with Jacob has to make sure elbows, hips, all squared up and rifle lined up straight, trigger finger at 90deg. Prone groups off dirt moved up 1/10 or 2/10 mil and left 1/10 mil and tight enough to hang on the refrigerator. This POI matches up much better with my wood deck and barricade results. Exactly what i was looking for.

Hopefully if weather holds out will hit the range this weekend and shoot 100yds from all positions and surfaces to check, but think its looking good.

Thanks for all the comments above