Newbie question: Expected zero change from ground to bench

[rogerg12]

I frequently go to my indoor range to shoot to 100yds, especially when I've modified my rifle to re-zero things in, before I head to my outdoor range. The indoor range only allows a bench setup for shooting (no laying prone). I'll get my 100yd 0 in tight, perfect. Then on a different date, I'll head out to my longer outdoor range which has targets up to 2000 yds. I'll often take a few shots at 100yds laying on the ground and usually find that I'll have to make some minor adjustments (just a mil or so) to regain that tight zero.

Is this expected?

Does the few feet change in elevation (from ground to bench) change things that I have to account for or am I just being a newbie shooter and not either zeroing like I should or not shooting as well as I should?

 

[JBoomhauer]

A mil? Hope you mean a tenth.

In short. Its likely just you.

 

[orkan]

If you're using correct positions... there should be no shift. In the below video, the first group was shot prone, the second group was shot standing over a bench. The adjustment to the scope was exactly what the conditions called for, and shots landed exactly where expected.

 

[W54/XM-388]

If you are a full mil off something is very, very wrong
If you are 0.1 mil or 0.05 mil off then it's your eye position relative to the scope's exit pupil.

 

[rogerg12]

A mil? Hope you mean a tenth.

In short. Its likely just you.

Yeah...sorry...at tenth...single click

 

[rogerg12]

Thanks everyone

 

[KnowNothing256]

Typically small POI shifts like you describe have to do with the surfaces that are supporting the rifle. If you have sandbags in front and back both indoors and outdoors, I'd expect zero shift as long as your body position and parallax were good in both seated and prone. If you're shooting with bipod in front and bag in back, and the bench is hard/solid and your outdoor range is in dirt or loose gravel, I'd expect your outdoor POI to potentially be slightly lower than indoor. The reason for this is, with relatively hard bipod feed and a bench that doesn't move, any vibrations in the gun during the internal ballistics phase can't move the gun anywhere but up, typically affecting the muzzle the most. This means the muzzle tends to "bounce" up, raising POI slightly. If you then take that system outside onto softer dirt or gravel, now those vibrations can be dissipated with less bounce, and your POI will be lower than your bench zero.

An alternative situation has to do with loading the bipod: if you're really leaning into the bipod in the prone, and less so on the bench (a pretty typical scenario), then you might see that POI shift in the opposite direction. Many bipods flex enough when loaded hard to actually lower your forend just a bit, then when recoil occurs the gun moves back, the bipod feet don't, and the muzzle lifts (imagine standing up a framed wall). If you are loading the bipod less on the bench, then this effect will be reduced or eliminated, and your bench POI would likely be lower.

 

[TheOE800]

There’s a @lowlight article about changing POI based on positional zero.

 

[pineoak]

Likely you're pushing the rifle differently in diff positions, loading the bipod differently, and without enough pressure behind the buttstock allowing recoil to redirect the rifle more.

as mentioned above, if you mean 0.1 mil or 1/10 of a mil, then this is normal and likely your positioning/technique

if a full 1.0 mil... either your equipment is suspect or you are not fully supporting the rifle from the back in a manner that controls recoil effectively