Low impacts in low light (update)

[Slash0311]

Short version. Ive got a good zero at 100 yards at my States Sniper School. Ive passed 7-8 quals up to tonight. We did a night shoot. One qual couse (passed) 16 rounds on 4 targets total (all impacted about 1/2" low) and then another qual. I failed the last one because 3 rounds were 2"-3" low and outside the scoring box. The only adjustment i made from daylight shooting to tonight was lower magnification.

I spoke to an instructor on the range. One suggestion was possible cheek weld change for lower mag. Or shadow.

I plan on asking more on it tomorrow and won't be able to check replies here till tomorrow evening. Anyone from the brain trust have any ideas?

Ruger Precision .308, 20" barrel
NF ATACR 4-16x50 F1
FGMM 168

 

[Deleted member 113831]

Short version. Ive got a good zero at 100 yards at my States Sniper School. Ive passed 7-8 quals up to tonight. We did a night shoot. One qual couse (passed) 16 rounds on 4 targets total (all impacted about 1/2" low) and then another qual. I failed the last one because 3 rounds were 2"-3" low and outside the scoring box. The only adjustment i made from daylight shooting to tonight was lower magnification.

I spoke to an instructor on the range. One suggestion was possible cheek weld change for lower mag. Or shadow.

I plan on asking more on it tomorrow and won't be able to check replies here till tomorrow evening. Anyone from the brain trust have any ideas?

Ruger Precision .308, 20" barrel
NF ATACR 4-16x50 F1
FGMM 168

What were the zeroing conditions? Lighting, mirage and height above ground?

 

[Slash0311]

Zero conditions were daylight, mirage was fairly low. Wind was about 5-8 hslf to full value. Nothing too crazy. That was Monday.

We have shot the same qual, relatively same conditions each day several times and each time I had no issue. Groups opened a little but all were passing... until last nights qual.

 

[Deleted member 10043]

Your simply shooting at what you can see.

 

[diverdon]

NF ATACR 4-16x50 F1

Could be a lotta things but NF's have problems none of the fanboys want to talk about. One is that several NF's I have used have changed the POI .2-.4 Mill depending on if the the last adjustment to the magnification was to increase vs to decrease. Of course perhaps I'm only imagining things.

 

[Slash0311]

Thats something I was thinking to check. Here on another qual or at home. Every qual I had ran till last night was on 16 mag... last night was at 4. Except for night, nothing else OBVIOUS changed...

 

[Deleted member 113831]

At first I was wondering if there might be a zero shift due to mirage, but that is a huge zero shift at that range. Given what you told me about zeroing conditions I don't think that is it. I would expect any mirage shift to be in the opposite direction going from day to night anyway. In other words, I would have expected you to hit high, not low.

IMO there is most likely a zero shift due to the magnification change.

 

[phlegm]

The first place I'd look for a mystery shift like this is parallax error - either adjustment on the scope or from a change in cheek weld.

 

[Slash0311]

Ive been conscious of parallax. Can't rule it out 100% but I'm still thinking it's related to cheek weld

 

[plidenbrock]

My first thought was the mag change zero shift, as @diverdon noted it happens more than folks want to admit, or perhaps even realize.

This is strictly my personal experience, but if you are assuming your FFP in the dark, things get a little weird.

Getting settled in perfectly becomes difficult to impossible in the dark, particularly if you are finding and assuming the FFP completely new in the dark. If your position has been found / used during the day, it's a touch easier.

You said the only thing that changed was mag range, so I guess that means you didn't utilize reticle illumination...but one thing I've learned is the value of illumination which lights the entirety of the reticle. The little detail that makes that important is that if you are properly focused and zeroed in daylight, then a reticle lit completely will show you an improvised "scope shadow" on the periphery which will allow you to obtain a proper cheek weld in total darkness.

For me, the thing I found was that my eye could see the hash marks lit up, and I can visually see which sides of the reticle were longer or shorter by the illumination, and can therefore adjust my cheek-weld in order to obtain proper centering. I've found that this mitigates the difficulties of perfect cheek weld and properly adjusting parallax in the dark.

That's just something to consider. I personally don't care for NF's illumination system for that very reason, but you may not even be using it.

Or who knows...since it was all low, it could be something as simple as dramatically reduced ambient temps of night-time cooling the ammo itself, leading to reduced muzzle velocity and a lower impact. That's something you'd have to consider. A seemingly small temp reduction could still account for some significant impact changes.

Just some more ideas for your consideration...

 

[Slash0311]

I was finally able to get to the range when the weather cooperated.

I shot a few rounds at 16X magnification and was spot on. I dialed my power back to 4X and fire a group. Point of impact did not change. I dialed up to 16X and shot another group. Again, spot on.

Granted this was daylight shooting but I feel I can rule out any shifts due to magnification. Id say it was me not mounting up correctly in the low light. Once I can hit the range at dusk, I'll try again and see for certain.

Thanks for the imput!

 

[Lowlight]

was it all 100 yards ?

Didnt see it posted

 

[Slash0311]

Yes. 100 yards.

 

[RTH1800]

Be interested in seeing how this mystery is solved. ???

 

[Milo 2.5]

I was finally able to get to the range when the weather cooperated.

I shot a few rounds at 16X magnification and was spot on. I dialed my power back to 4X and fire a group. Point of impact did not change. I dialed up to 16X and shot another group. Again, spot on.

Granted this was daylight shooting but I feel I can rule out any shifts due to magnification. Id say it was me not mounting up correctly in the low light. Once I can hit the range at dusk, I'll try again and see for certain.

Thanks for the imput!

For me, on all NF scopes I have owned, from NXS to F1 Atacr's, at about 45 min before dark, reticles start to fade away( not totally sure how to explain this), and for around 20-25 min it I struggle bad with it. Then about 20 min before lights out it comes back nicely, and usually the sun is at my back. I do not know if it is the scope, or my eyes. It would be rare for me to be shooting at 100 yards though. All my scopes I own are illuminated, a feature I never use.
I have gravitated to Kahles optics today because of this.