Bench rest effects zero?

[DeepFried]

Recently installed a new optic on shadow 2 OR. Zeroed at 15 on the bench and confirmed it at 25 from the bench. Never got a chance to shoot it much after. 
 

today I was shooting it at 10-15 and was consistently low 1-2”. Did a quick group at 15 standing, no bench rest, and decided to go ‘up a few clicks’ because group was certainly low. Now POA = POI

 

before leaving decided to do a 5 round group at 15y bench resting on a chunk of 4x4 to confirm one last time. 
 

im hitting high! The exact amount I was low earlier. The exact amount I adjusted. 
 

in theory I can maybe understand resting the pistol on something effects POA, POI, accuracy..but I’ve never seen this in my previous plastic gun shooting and the dust cover on shadow 2 is super heavy duty. 
 

Anybody experience this?

Edited August 15, 2023 by Seoderus

[Joe4d]

angle of face to dot different ? You getting dot in middle of glass ? When you say bench what are you benching ? Is the gun on the block or rest ? When I confirm zero I only have my arms on the  rest, nothing touching gun

[Dr. Phil]

You might see a difference if you were to rest on a sandbag or similar. The gun will tend to recoil (lift off) of a hard surface. 

Worth a try to know in the future.

[DeepFried]

Gun rail/dust cover touching wood block or sandbag (sandbag when I did initial zero and block for quick check yesterday). 
 

bottom of mag/my hands sort of touching the table. And forearms mainly doing the ‘bracing’ on table edge. 
 

have used this method on all other red dot pistols, mostly Glock, never any difference in POA POI. Very confused. 2” at 15 is huge

[858]

Which optic? Parallax?

[DeepFried]

5 minutes ago, 858 said:

Which optic? Parallax?

507comp

 

maybe? Dot is centered in window since I am taking my time to shoot best groups. Have zeroed other holosun offerings no issues..

 

do want to replace with 5moa SRO though, prefer it. 

[858]

26 minutes ago, Seoderus said:

507comp

 

maybe? Dot is centered in window since I am taking my time to shoot best groups. Have zeroed other holosun offerings no issues..

 

do want to replace with 5moa SRO though, prefer it. 

 

Parallax is from changes in eye position behind the optic, not necessarily where the dot is observed in the window. All of these sights have parallax to some degree, some worse than others. I don't know if that is what you're experiencing though, I'd probably just confirm zero the way you would shoot the gun at a match. FWIW, I struggle shooting pistols from bags regardless of the sight.

[fbzero]

I've typically viewed shooting from a rest as a way to determine the accuracy potential of a reload, but always sighted in free style.  Might just be a logical thought that has no basis in reality, but my assumption has always been that since the firearm is likely to recoil differently and I will be braced differently, it may alter POI.  If I sight in free style with my normal grip, then this should not be an issue.  

 

 

 

 

[shred]

I see small zero changes with comp guns off a rest, but it's minimal.  Much larger factor is where I'm looking through my glasses-- the benches around here are about 4' tall so I have to hunch down and lean over to use a rest-- which puts my eyes looking through a different part of the glasses than standing on two feet, so I do accuracy tests off a rest, but final zero standing.

 

Also if you have prescription glasses, occluded vs not-occluded dot can change POI.

 

 

[DeepFried]

All good points and make sense. The thing I can’t figure out is why I’ve never experienced this before. It must be related to the optic or my eyeballs not the pistol

[hlsccsfa]

On 8/15/2023 at 6:24 AM, Seoderus said:

Gun rail/dust cover touching wood block or sandbag (sandbag when I did initial zero and block for quick check yesterday). 
 

bottom of mag/my hands sort of touching the table. And forearms mainly doing the ‘bracing’ on table edge. 
 

have used this method on all other red dot pistols, mostly Glock, never any difference in POA POI. Very confused. 2” at 15 is huge

 

Same with my S2, and in the past, with my M&P. With my experience, in order to simulate standing off-hand shooting when zeroing with bench rest, I rest my upper arm on my range bag to provide support, and my elbow, forearm, hand, and the pistol touch nothing. Not sure how to explain it in a scientific way, but this way the POI is the same as standing off-hand shooting.

 

[tim_w]

It's not the gun/rds mechanically POA/POI or parallax even though some of the RDSs have TERRIBLE parallax (MRO as an example).  It's usually recoil management of the person in the situtation presented.  You will even see this shooting FTR Class  1k, especially 308 trying to use the heavy 200-230gr.  Even with fancy bipod, rear bags, etc  on a precision bolt gun.  Shoot a few rds not coming off the rifle.  Then stop, get up, reposition the rifle and yourself, put those crosshairs on the same spot and fire.  You will likely see a small change in POA/POI.  Even the slightest changes effect POA/POI relationship. Now, imagine with handgun going from fixed rigid bench support to freestanding with arms not supported at all.  Recoil management is going to change significantly. How the gun moves on intial recoil will be different before bullet clears the muzzle. 

[DeepFried]

I changed optics and the problem no longer exists. 
 

not sure if ‘parallax’ is the right word but there was obviously something going on. 
 

as mentioned in previous posts I’ve used this method on many pistols to sight in dots and never had an issue. The replacement dot also has no issue. Make of it what you will.