Zeroing and bench lens distortion

[JCN]

So I was testing a PMM barrel for a P365 today and noticed significant vertical stringing from a rest.

Turns out the RMSx has quite a bit of shift distortion towards the top and bottom that changes POA/POI.

All the shots were perfectly in line, just strung.

So I changed to an EPS Carry and I really paid attention. I could see about a 2” shift at 25 yards in where the dot was when it got closer to the upper 1/3 of the lens.

This speaks to what @GJM was saying about head position really mattering.

So I played around with dot placement in the window to find the area that was least distorted and took shots using that part of the lens.

I’m happy to say that answered the question of whether my PMM barrel shoots well with 124 +P Gold Dot.



@YVK ymmv

@GJM I know you still have doubts of a 3 shot group, but I shot a lot of 124 Federal and a handful of rounds of the 124 +P Gold Dot testing this hypothesis.

No fliers. Just vertical stringing when the dot was in a part of the lens with distortion.



So for red dots, this is a thing. @SoCalDep Something I didn’t really appreciate the amount of contribution.

With the EPS it wasn’t even super close to the edges, even using the top 1/3 of the lens put me in a zone that had 2-4” shift with even a small movement. @Clusterfrack

[JCN]

Tomorrow I’m going to use a B8 and the circle dot reticle to try and get even more consistency in placing the zero in the center of the window. I can use the outer ring to be a little more consistent in relation to the front sight and the top of the window to see if I can get things more centered.

[YVK]

I've been dry firing my 365 nearly daily and I am pretty confident in my trigger press. I am even more confident in my ability to call bad trigger presses off the dot when shooting slow groups. Tomorrow I should get a replacement of my S&B ammo, that I shot a 2 inch group with out of PMM last week. Maybe I'll make it to the range over the weekend, maybe not. If I do, I'll keep my dot centered.

Independently, Charlie Perez posted on Enos something about POI shift when the dot is off the center. Some optic he's using, supposedly better than other.
I've no time to test everything I want to test.

[Archer1440]

For literally decades, various manufacturers have claimed "zero parallax" for various reflex sight devices. I think that has created a general sense that there really is no parallax that needs to be considered, in the minds of many less experienced users.

The truth, however, is that every reflex sight (I am not talking about holographic reticles here, but reflex sights) has some amount of real-world parallax error when the dot is viewed out of the center of their respective objectives at various distances.

The question is, "is it enough to make a difference", which comes down to time, distance, and the precision required to accomplish a specific task.

If you have time, then you will always get the most precision by keeping the dot close to the optical center of the window, regardless of the reflex optic being used. If distance is shorter, and time is less, you can still accomplish certain tasks adequately, though with less precision.

Of course the same principle applies to ANY sighting system. Red dots are not "magic bullets", sight alignment and the principles of marksmanship still fully apply.

In the case of RDS systems, this specifically means centering the dot in the window as best you can, given the circumstances of time and distance for the particular problem.

That will be obvious to most of the more experienced users here, but I often run into shooters who really don't know that.

[CCT125US]

You can also observe shift with a bore sight using the relative position of the two dots.

My Swampfox Sentinel M would shift the size of a B8 9 ring at 25 yards if I worked the dot off the outer edge of the optic body. Interestingly, the Riton MPRD will only shift the 10 ring.

[JCN]

My Swampfox Sentinel M would shift the size of a B8 9 ring at 25 yards if I worked the dot off the outer edge of the optic body. Interestingly, the Riton MPRD will only shift the 10 ring.

In the case of RDS systems, this specifically means centering the dot in the window as best you can, given the circumstances of time and distance for the particular problem.

That will be obvious to most of the more experienced users here, but I often run into shooters who really don't know that.

I think the thing that I didn't realize is how different the amount of shift is with different optic brands and models.

I've been spoiled with mainly using SRO and DPP which don't shift very much to matter... but the RMSx was terrible and the EPS carry was still significant!

[LittleLebowski]

Do you have corrected eyesight?

[JCN]

Do you have corrected eyesight?

I do! I try and view the optic through the same place in my eyeglasses.

I specifically picked the model of regular and shooting eyeglass frames to have larger lenses and closer to eyeball fit so that my eyes stay more centered in the lenses.

[Archer1440]

Do you have corrected eyesight?

It should be noted that, contrary to “common sense”, the specific parallax shift of any given reflex optic is not related to optical distortion from corrective lenses. Counterintuitive but easily proven.

[ViniVidivici]

Very interesting, but not surprising. I always figured for zeroing, keep the dot in center of window.

Consistent head position is one of the lessons I've had to learn when it comes to precision at farther ranges, especially when applied to rifle. My groups 200 yards and out shrank when I really welded my head to the stock for the entire string

It IS surprising to see the amount of variation between brands. Makes sense though I guess if you really think about the minute structural differences in them.

And heck yeah, Speer 124gr GD, both +p and standard, are like laser beams out of my guns, amazingly accurate load. That and good ole' 9BPLE are the most accurate factory loads I've yet shot.