Thermal shifting while ranging

In FT it is soooo important to range correctly (know your distance) for correct holdover or POA. I have experienced the frustration of setting up various scopes - hawke, sightron, athlon, Aztec, Swfa and even a March in my heated and cooled cave/shooting lair @74 degrees, where I can range focus from the comfort of my shooting bench out a window for at least 85 yards. I then go outside to practice my FT game on bucket and sticks in 80-95 degrees weather; only to discover my range wheel markings are now “off” 🤔
Comfort be damned - looks like I’ll have to set up my ranging wheels outside or figure out a way to know how much the thermal shift is throwing off my distances.
Thoughts?
 
In FT it is soooo important to range correctly (know your distance) for correct holdover or POA. I have experienced the frustration of setting up various scopes - hawke, sightron, athlon, Aztec, Swfa and even a March in my heated and cooled cave/shooting lair @74 degrees, where I can range focus from the comfort of my shooting bench out a window for at least 85 yards. I then go outside to practice my FT game on bucket and sticks in 80-95 degrees weather; only to discover my range wheel markings are now “off” 🤔
Comfort be damned - looks like I’ll have to set up my ranging wheels outside or figure out a way to know how much the thermal shift is throwing off my distances.
Thoughts?
Yeah unfortunately, you gotta range in different temperatures to calibrate your scope. If you google, you'll see some competitors have two different pointers for their side wheel for different temperatures (I heard the earlier Schmidt Benders were notorious for thermal shifts). They also taped those aquarium temperature strips onto their scope to tell them what the scope temperature is and which pin to use.

1687011028255.png

I don't shoot hunter class, so I don't know how critical ranging is at different temperature at 16X.
But shooting at 50X and ranging the longer distances 40-55 yards...I do see 2-3? yard shifts at higher temperatures at these distances (but I haven't calibrate my scopes at higher temperatures).

This discussion prompted me to look at my data for all my matches. I was looking at my miss percentage for FT matches from January to now (45- 55 yards). 50-100% miss rate hmmm could be wind related?...could be ranging error?... might be the next project? After I research and make a decision on weighting and lubing pellets (another rabbit hole).
 
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We see thermal shift at our club esp in winter when we shoot indoors and the scopes are coming up to temp from “truck cold”. It has shown as a sudden shift in poa.

I too have heard March are highly resistant to it. Fortunately their scopes do focus down to 10y so if that’s a big concern for you, that’s a workable solution.
 
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In FT it is soooo important to range correctly (know your distance) for correct holdover or POA. I have experienced the frustration of setting up various scopes - hawke, sightron, athlon, Aztec, Swfa and even a March in my heated and cooled cave/shooting lair @74 degrees, where I can range focus from the comfort of my shooting bench out a window for at least 85 yards. I then go outside to practice my FT game on bucket and sticks in 80-95 degrees weather; only to discover my range wheel markings are now “off” 🤔
Comfort be damned - looks like I’ll have to set up my ranging wheels outside or figure out a way to know how much the thermal shift is throwing off my distances.
Thoughts?

I have known that the zero parallax setting changed with temperature for at least 30 years, but it didn't have any impact on range estimation since I never used the parallax setting position on a riflescope to estimate range. I am sure there was some POI change due to temps but I wasn't a good enough shot to tell the difference.

This explains why the yardage markings on a parallax dial are just "ballpark" distance markings and also why some makers don't put actual yardage numbers on the dial, just larger to smaller markings indicating longer to closer distances, since the actual zero parallax setting is constantly changing with various temperatures.
  • Which March model do you have? The March High Master glass system is said to have less temperature shift than their regular ED glass. I have not tested it myself.
  • Did you ever find that you could not focus at 10 yards at some temperatures and could at others? Some of my scopes travel closer than the 10 yard marking, some do not.
  • How much off were the settings on your dial compared to the marking from indoors to outdoors at higher temps?
  • Was there more of a distance on the dial shift at closer or longer ranges?
  • If a parallax dial stops abruptly at 10 yards, have there been instances where you could not dial out the parallax completely at 10 yards because of that? Some of my scopes have movement past 10 yards in the closer range, some do not.
  • For the highest precision, it sounds like you would need to calibrate your dial for several different temperature ranges.
  • It would be interesting to see how much of a change on the dial there is with every 10 to 20 degrees in temperature. I don't have an oversized dial yet, so can't experiment with it myself.
Feel free to ignore the rest of this as it has nothing to do with the original thread. :eek:

For long distance ranging I had a 300 to 30,000 meter Wild optical rangefinder made by Deutsche Optik and some Russian made Newcon rangefinder binoculars that ranged to 2500 yards IIRC which was the longest ranging electronic device under $2000 at the time - in my early years of 1000 to 2500+ yard shooting back in the 80s, I remember reading in an owner's manual for some high dollar scope where it explained why the parallax focus mechanism markings traveled beyond the "Infinity" symbol, because there is no exact yardage associated with the dial position for a zero parallax point - always shifting due to temperature changes. They explained that as the temperature shifts, so does the parallax free set point - thus the extra movement past infinity. I can see how that might mess things up when ranging for Field Target based on calibrated markings.


1687015003176.png


My Wild looks just like this one. Quite accurate for a 60 year old mechanical / optical device. It weighs more than quite a few of my long range rifles and is not fun to carry. If it was deployed at some shooting ranges, I am sure the rangemaster would be running over to stop us from shooting that RPG or Bazooka!

The bar with the squares on either end at the bottom of the photo were used for calibration, which I assume likely reduced errors caused by the current temperature, though I didn't calibrate it in the field very often. In use it is perpendicular to the line of sight and you look down into the eyepiece to take a reading.

This video on YouTube, is on a 1942 WW2 vintage Barr and Stroud brand, but the function is similar to the Wild. Another video on Youtube that talks about the mechanics a bit used in this type of rangefinder. The Wild uses a split image type of display like what is found in older cameras.
 
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The refractive index of air changes with temperature, so the focus points will change too. Also the parts expand and contract and change dimension altering focus as well. I suppose with more careful design choices and materials much of the temperature affects can be mitigated at a higher cost and weight penalty. That's why even some high end scopes don't put range markers on the parallax knob, it would be misleading at best.
 
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I used a sightron 4-20x50 for a while. The ranging on that scope shifted quite a bit in large 30° temp shifts. I haven't noticed this as much with Hawke or Athlon scopes. On the west coast where I shoot, the avg temps I shoot at are between 50 - 100°. I usually just try to range a scope in the middle around 75°. I have enough things to consider when shooting FT that I really don't need another :p
 
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Today, it's Fathers Day, and I reset my entire FT ranging and target course from 10-55 yards; all clearly marked in a variety of optical bliss (ha).

i am going to leave my Tsar FT with my Sightron SIII 10-50x60 outside in the 90 humid air for a couple hours but under cover. After this i will begin parallax focusing / ranging and marking my range wheel anew. I will mark the scope wheel left in 90 Degree temp's with a fine tip red perm ink - RED to indicate HOT, at first my biggest focus will be in 5 yard increments.

I will then return the Daystate Tsar to the A/C of my indoor 75 degree mancave, and after 2 hours of cooling down I will repeat my ranging from inside the comfort of my shooters box window set up with emphasis on 5 yard distances, but this time i will mark the wheel with a green fine tip perm marker.

I can then turn the A/C down to 60 BRRRRRRR and after 2 hours of acclimatizing i will repeat the process but this time i will use a fine tip blue marker (indicating cold) with emphasis on 5 yard intervals. Actually there is no rush on cold weather markings as December - February are a long way off.

This should prove enlightening.

Note the Athlon scope in the picture predates my New Sightron. If this exercise proves useful i will repeat with my other primary FT rigs.

Of course i could set one complete rig up for 50 degree weather, another for 60 degree weather, another for 70 degree weather, another for 80 degree weather and so on.... glad i don't live where its always cold or gets into the 100 plus temp often.
Can we obsess ? Yes!
Afterall it's Fathers Day.
IMG_5640.JPG
Perhaps the Frankenraw will need the same love:
90ED803E-3D9A-4C92-86AD-4BC493C0B84F_1_105_c.jpeg
 
I have known that the zero parallax setting changed with temperature for at least 30 years, but it didn't have any impact on range estimation since I never used the parallax setting position on a riflescope to estimate range. I am sure there was some POI change due to temps but I wasn't a good enough shot to tell the difference.

This explains why the yardage markings on a parallax dial are just "ballpark" distance markings and also why some makers don't put actual yardage numbers on the dial, just larger to smaller markings indicating longer to closer distances, since the actual zero parallax setting is constantly changing with various temperatures.
  • Which March model do you have? The March High Master glass system is said to have less temperature shift than their regular ED glass. I have not tested it myself.
  • Did you ever find that you could not focus at 10 yards at some temperatures and could at others? Some of my scopes travel closer than the 10 yard marking, some do not.
  • How much off were the settings on your dial compared to the marking from indoors to outdoors at higher temps?
  • Was there more of a distance on the dial shift at closer or longer ranges?
  • If a parallax dial stops abruptly at 10 yards, have there been instances where you could not dial out the parallax completely at 10 yards because of that? Some of my scopes have movement past 10 yards in the closer range, some do not.
  • For the highest precision, it sounds like you would need to calibrate your dial for several different temperature ranges.
  • It would be interesting to see how much of a change on the dial there is with every 10 to 20 degrees in temperature. I don't have an oversized dial yet, so can't experiment with it myself.
Feel free to ignore the rest of this as it has nothing to do with the original thread. :eek:

For long distance ranging I had a 300 to 30,000 meter Wild optical rangefinder made by Deutsche Optik and some Russian made Newcon rangefinder binoculars that ranged to 2500 yards IIRC which was the longest ranging electronic device under $2000 at the time - in my early years of 1000 to 2500+ yard shooting back in the 80s, I remember reading in an owner's manual for some high dollar scope where it explained why the parallax focus mechanism markings traveled beyond the "Infinity" symbol, because there is no exact yardage associated with the dial position for a zero parallax point - always shifting due to temperature changes. They explained that as the temperature shifts, so does the parallax free set point - thus the extra movement past infinity. I can see how that might mess things up when ranging for Field Target based on calibrated markings.


View attachment 365331

My Wild looks just like this one. Quite accurate for a 60 year old mechanical / optical device. It weighs more than quite a few of my long range rifles and is not fun to carry. If it was deployed at some shooting ranges, I am sure the rangemaster would be running over to stop us from shooting that RPG or Bazooka!

The bar with the squares on either end at the bottom of the photo were used for calibration, which I assume likely reduced errors caused by the current temperature, though I didn't calibrate it in the field very often. In use it is perpendicular to the line of sight and you look down into the eyepiece to take a reading.

This video on YouTube, is on a 1942 WW2 vintage Barr and Stroud brand, but the function is similar to the Wild. Another video on Youtube that talks about the mechanics a bit used in this type of rangefinder. The Wild uses a split image type of display like what is found in older cameras.
Wow - that’s a lot of questions!
What I discovered yesterday while working with the Sightron was the longer the scope was outside or coming up in temp, the greater the change in focus / ranging became! 3 yards from 74 degrees to 84 degrees-this amount of change varied at different distances but I can clearly tell that an FT gun relying on parallax to determine distances really needs to be set up for the temperature it will be operating in, especially on a day of competition.
 
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Wonder if it's worth it to Red Neck a temperature controlled scope "case/sock" with a built-in heater/AC with fan to encase the scope. Then just remove the scope case when ready to shoot. Or if it's a light weight sock type design...shoot with it on.

OR

A temperature controlled gun case. Just set it and forget it. Might have to shoot quickly once out of the case before the heat or cold affect the scope... then quickly back in the gun case. (WFTC Italy 2022 would have been a great test site for this device)

--
(Now I'm really going crazy...too much time on my hand)
A solar powered climate controlled umbrella/tent with heater/AC and fan built in. With battery back up for those rainy days. Keep your fingers, toes and scope toasty (or chilled) while you shoot.
--
That temperature controlled gun case is highly doable with off the shelf components (temperature sensor tied to a heater/AC fan) . Wondered if someone already patented and are manufacturing these...or am I the first?
 
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Wonder if it's worth it to Red Neck a temperature controlled scope "case/sock" with a built-in heater/AC with fan to encase the scope. Then just remove the scope case when ready to shoot. Or if it's a light weight sock type design...shoot with it on.

OR

A temperature controlled gun case. Just set it and forget it. Might have to shoot quickly once out of the case before the heat or cold affect the scope... then quickly back in the gun case. (WFTC Italy 2022 would have been a great test site for this device)

--
(Now I'm really going crazy...too much time on my hand)
A solar powered climate controlled umbrella/tent with heater/AC and fan built in. With battery back up for those rainy days. Keep your fingers, toes and scope toasty (or chilled) while you shoot.
😵‍💫
 
Solution-! Buy JD Garland’s parallax wheel x4 but just one hub. Mark/calibrate the 4 different wheels for 4 different temperature ranges. This is an example:
50-65 degrees
65 to 75 degrees
75 to 85 degrees
85 to 95 degrees
Once the hub is installed you can pop your wheels on and off according to temperature range on day of competition because the hub always puts the wheel back in the exact same spot. Now knowing the actual temperatures where the shift occurs is another rabbit 🕳️.
 
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I changed my big parallax wheel on my Athlon Talos 6-24 to use a stick on measurement tape. It is marked in mm. Then I have to determine what mm = what distance. For casual shooting, I have a stick on label on the inside of the objective scope cap with the mm, distance, and hold over (at 6X and 16X). If I ever actually shoot hunter FT my plan would be to have a more detailed card with more detail than I can put on the little sticky disk.

It seems like that system would be an advantage relative to temperature shift. The mm for a distance might change a little but with multiple cards prepared that vary by temperature I would be set.
 
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Simply KNOWING in which direction shift happens, or better wrapping ones mind around which directions the ranging errors happen ( Zero range & Closer / Zero range and farther ) you stop aiming in the center of KZ :oops: And place your POA in a corrected position to mitigate the most error probability if present.