Scope & Temp Shifts

Am actual Question about repeatable temperature shift?

It's like saying you know your reg creeps with the first shot after stored then you compensate to always hit dead on for that first shot?

Some scopes range long in the cold, and short in the heat, others are the opposite. March scopes for example, usually range long in the cold, and shorter in the heat. Most optics I have tried for FT are actually the opposite though, where they will range short in the cold and long in the heat. It's something that is usually consistent among the same brand, but not across all scopes.

But in general, if a scope is temp sensitive (and most are to some degree) that shift will always present itself in the same direction for that optic. The bigger question that must be tested is how much shift occurs based on temp change. For example, I set up a scope at 70F, between 60F and 80F it's stable and ranges the same as my initial markings. When the temp drops between 50F-60F, the scope ranges long by 1-2mm on my sidewheel compared to my "normal temp" markings. But then when the temp drops below 50F, I notice the scope now ranges another 2mm longer than my "normal markings", so 3-4mm total. Flip that around, and when it's between 80F-90F, I am ranging 1-2mm short, and then anything above 90F, I am ranging 3-4mm short. This is a more extreme example, but one I experienced with a March 10-60x52 many years ago. Fantastic scope, but I had to learn the temp shift to really get comfortable with it and have success. And thankfully the shift was consistent enough where I could correlate the shift and my ranging to an on-board temp gauge and that system worked pretty well for me.

Hopefully that made some kind of sense. Test for yourself with your scope and see what you see.

Great info from Tyler there.

If it matters for the job at hand, bear in mind whatever shift you experience is the combined result of a variety of factors. Not just due to the scope but also the expansion and contraction of a number of different components (scope mounts, receiver, barrel, etc.), any temperature sensitivity of the powerplant (springer’s piston seal or a PCP’s hammer and any lubricant) and so on. As a practical matter, about all you can hope to do is characterize the gun & scope combination as a complete system. 

In other words if you had an interest in testing scope A and scope B to see specifically how much shift each contributes for X change in temperature, that would be better accomplished by a purely optical means. For example, you might mount the scope to a rigid object and focus it onto a grid on a cold day, and then take a heat source (hair dryer) and warm it up and see how much it moves against the grid. Whatever mounts are holding the scope is of course still a contributor to the total POA shift so steel would be preferable to aluminum (approx. half as much thermal expansion). And a camera instead of your eye to help weed out any parallax error that remains.

Just food for thought…I expect that second part goes way beyond what you’re looking for.

My Field Target scope is Schmidt and Bender 10-50 first generation. It got bad press because it was temperature sensitive. In all other respects, it's a real nice high end scope.

To compensate for temp changes I bought a adjustable 3D printed pointer from Maestro in UK. He has several models. Mine was made for the Schmidt and Bender. I can now calibrate for current temperture conditions. It works just great.

My Burris R/A (Rimfire/Airgun 8-32 scopes allow you to also calibrate with their factory printed yardages. Why don't all mfg's do this?

Fixed power scopes like my Nightforce 36X are never affected by temperature. I am fortunate to own 3 Nightforces and 4 Burris R/A's.

LMK when you get tired of the 4 Burris R/A scopes.