ES and SD

[Rhovee]

I would say anything around a 20 es and sd of 10 would be considered ok.

 

[Pdvdh]

I'm trying something a little different with my newest project. My sample consists of only cold bore velocity readings over a range of environmental temperatures to see how much temperature affects my first shot velocity with RL26 in a 300 WM.

It has been eye opening. For those of you worried about temp swings with RL26, you really shouldn't be. My Berger 215 load has shifted 2 fps with cold bore shots ranging from 28° up to 56° so far.

Have you checked POI also. I did this with 5 different rifles last winter. Good way to collect Temp Vs MV data. I ensured the rifles and ammo both came down to ambient temps. I ran the tests down to 0F, even though I don't hunt in those temps. RL 33 was good until the temps dropped below ~25F.

But the #1 lesson for me was the minor POI shifts from routing outing to routing. I did this over about a 4 month period of time. Not large POI shifts. One scope click was pretty common @ 300yds. 2 clicks was not uncommon. Learned either the lighting or the temps or both, contribute to minor POI shifts with my rifles. One rifle was more stable than the rest. But not immune. All custom rifles.

And to clarify, I mean most every outing, which was normally different weeks, temps, and lighting conditions, I observed minor POI shifts with most all rifles on paper at 300yds.

 

[brentc]

I've encountered strange POI shifts in the past in different conditions with some of my rifles. I always attributed it to load variance, but for me, it came down to parallax and specifically the rifles with NF NXS scopes. Once I moved away from the NXS, POI shift was no longer a problem.

 

[Greyfox]

I've encountered strange POI shifts in the past in different conditions with some of my rifles. I always attributed it to load variance, but for me, it came down to parallax and specifically the rifles with NF NXS scopes. Once I moved away from the NXS, POI shift was no longer a problem.

I have experienced this as well. What scope/s are you using?

 

[cjl2010]

Brent, keep us posted on temp swings above 80°.

 

[Pdvdh]

I've encountered strange POI shifts in the past in different conditions with some of my rifles. I always attributed it to load variance, but for me, it came down to parallax and specifically the rifles with NF NXS scopes. Once I moved away from the NXS, POI shift was no longer a problem.

Thanks for sharing your experiences.

No Nightforce scopes here. Never owned one.
The scopes on my rifles are:
2 - Swarovski Z5 3.5-18X 44mm
3 - Sightron SIII 6-24X 50mm

Parallax would be a possibility, and could be the culprit. All 5 scopes have parallax adjustment.

One more piece of information: After 5 times out, I more or less concluded that the POI shifts were some sort of background noise due to shooting at/under differing temps/lighting/times. Because the POI shift didn't continue to walk away from the bullseye, and the shifts were all relatively small, compared to what one would expect with broken scopes or other flawed equipment. Left one day, right the next time, or up and then down the next time out. When all was said and done, it was minor shifting around the bullseye and I stopped adjusting the turret and just collected/recorded the POI data. POIs were more or less shifting around the rifle's true zero. The POI shifts from trip to trip created groups sizes substantially larger at 300yds than each gun will shoot in a single session at that same target/range. So..., after considerable time, thought, and evaluation..., ultimately I gave up. The scopes aren't broke. The rifles aren't broke. My loads aren't broken.

I experienced this with each rifle. One (338 Lapua Imp.) rifle showed less POI shifting than the other 4. But still, it was there. This is something a lot of guys wouldn't notice. I'd never confirmed it before after 40yrs of rifle shooting. But I'd never tested my rifles for POI shifts with single cold bore shots in various temperature conditions like this before. I think I went out about five different times with all rifles when the temperature was right to collect a new Temp versus MV test. I was specifically also testing POIs, because I think I had a suspicion that minor shifts in POI have been part of my life experience. I also wanted to learn exactly what cold bore accuracy to expect from each rifle over time.

I couldn't deny that the POI shifts were real. I was left with the conclusion that it may simply be the nature of the beast. I live in Alaska also, and you know we get some unusual sunlight angles during the winter, with the sun being so low in the sky. Others have expressed their suspicion that differing sun position can cause these minor POI shifts. Some experienced and capable marksmen claim they've experience this when comparing POI from morning to evening shooting events. I wish I knew the cause so I could prevent, or at least minimize, the POI shifts. Dunno...

As it is, I expect some minor POI shifting. I try to shoot my rifles to confirm zero after arriving at my hunt location, shortly before walking in for the spot and stalk hunts so common in the mountain terrain I frequent/hunt. That's the best I can do, until and unless I can otherwise determine the cause and adjust for it.

 

[brentc]

I couldn't deny that the POI shifts were real. I was left with the conclusion that it may simply be the nature of the beast. I live in Alaska also, and you know we get some unusual sunlight angles during the winter, with the sun being so low in the sky. Others have expressed their suspicion that differing sun position can cause these minor POI shifts. Some experienced and capable marksmen claim they've experience this when comparing POI from morning to evening shooting events. I wish I knew the cause so I could prevent, or at least minimize, the POI shifts. Dunno...

This is interesting and worth looking into more. There might be something to this. I know mirage wreaks havoc on POI.

My observations were from shooting groups at different distances during the same shooting sessions on different days, not just cold bore shots over a period of time.

As it is, I expect some minor POI shifting. I try to shoot my rifles to confirm zero after arriving at my hunt location, shortly before walking in for the spot and stalk hunts so common in the mountain terrain I frequent/hunt. That's the best I can do, until and unless I can otherwise determine the cause and adjust for it.

This is common practice for me too.

 

[brentc]

I have experienced this as well. What scope/s are you using?

I replaced my NXS scopes with two Vortex AMGs and a March.

 

[Pdvdh]

I replaced my NXS with two Vortex AMGs and a March.

Dang! I hope that eliminates any problems related to your scopes.

My scopes are in the category where I think I can still blame them, rather than myself!

 

[brentc]

Brent, keep us posted on temp swings above 80°.

Will do.

 

[Greyfox]

I replaced my NXS scopes with two Vortex AMGs and a March.

Interesting. My hunting rifles have March 2.5x25x52, and two Huskemaw 5x20x50's. My PRS rifles have Vortex AMG and NF ATACR/F1. These all have "fast ratio" parallax/focus turrets in common, and I experience no zero shifts with these scopes.

 

[Rhovee]

Personally I would have a hard time with varying cold bore shots and poi shift and not have the shooter come into play. It happens to me for archery as well. Always better when you warm up. After you get some shots down range, do you find yourself adjusting your scope back to where you started?

 

[Greyfox]

Personally I would have a hard time with varying cold bore shots and poi shift and not have the shooter come into play. It happens to me for archery as well. Always better when you warm up. After you get some shots down range, do you find yourself adjusting your scope back to where you started?

I will very rarely, if ever touch my scopes zero. I'll work with my rifle to the extent that I trust it's accuracy MORE then I trust my shooting capability. Whether in the field, or competition this forces me to concentrate and focus on "one shot". I'm rarely able to get any warm ups when I hunt, and can find my shot coming up after sitting motionless for several hours in freezing temps.

 

[Pdvdh]

I was taking 3-5 rifles out each shooting event. Allowing each rifle and ammo to come down to outdoor ambient temps, and then shooting each rifle one time while recording velocity and POIs. Sometimes I'd shoot a rifle a second time.
So I'd be firing ~5-7 shots each trip.
Not trying to convince anyone of anything. Your rifle outfits may be flawless. The minor POI drifts I observed were the norm, and repeated with a 2nd shot, in some instances. Not enough to be problematic on large game out to 450yds. I concluded it is what it is. Have any of you ever done this before? Take 5 rifles out 5 different times in variable temperatures and lighting conditions, over a period of several months? Run this test?
Didn't think so... It takes a fair amount of time and effort.