Rifle Scopes Optic/Scope hot/cold affecting POI?

[KiwiShtr]

I have a theory/question to get some opinions.
Lets say you have your rifle set up on the mound. Its 8am, over cast cloudy sky's and about 70f. You check your zero and all is good. Hypothetically, XX mins later, the clouds move off, sun comes out and it gets up to about 90-100.

Metals expand and contract in relation to temperature, some more than others. Most optics are also black thus absorbing heat. My scope (a S&B) can go from cool to hot to the touch quite quickly.

So theoretically all things being equal, would/could the change in ambient temp or shade/direct sunlight affect the optic and thus the POI?

I hadnt noticed it, but thought it could possibly happen. Any thoughts on this?

 

[sinister]

Re: Optic/Scope hot/cold affecting POI?

Shoot a morning match for practice and the same course of fire in the afternoon for match score after everything's warmed up.

POI will change. Will it matter with a full-size silhouette target (like a Figure 11)? Probably not. Will it affect your X-count (or whatever the Commonwealth calls their center ring)? Most certainly.

 

[Tactical]

Re: Optic/Scope hot/cold affecting POI?

Dave, they call them "V Bulls"

OP, its mirage and it causes a false aimiing point. Mkaes target appear higher than it actually is

Plus you have
normal shadow effects of different light conditions

Ammo/air temps causing higher velocities/point of impact

 

[prplhaz72]

Re: Optic/Scope hot/cold affecting POI?

It is a good question, good info you know.

The problem is, how do you know it is just the scope. Your barrel, action, rings and base, ammo, and scope all heat up. I am sure all of it can and does have a factor in a POI shift.

That is one reason I like to paint my guns and scopes a light tan color, they don't get near as hot. At least to the touch.

 

[felderthewelder]

Re: Optic/Scope hot/cold affecting POI?

I would say that you would get more POI shift from the gun heating up (and air heating up, and changing density etc.). I have seen people shooting competitions with a little shade over their barrel so that the top and bottom of the barrel don't warm up unevenly. But in shooting competitions you can go on forever with tricks to get ahead of the other competitors. I have no actual experience with testing to see how much the difference is with some of this stuff.

 

[Grump]

Re: Optic/Scope hot/cold affecting POI?

A LOT of these thermal expansion factors cancel each other out, or are most apparent on the LONGEST axis which happens to not change a thing on elevation or windage.

To the OP, you're not the first deep thinker to go down this line of inquiry. If it were a factor for zero shift, it would have been observed, noted and maybe even measured by now, and also as common knowledge here as the dreaded "spin drift" or mechanical physics-related coriolis effect.

But you would never have found this out without asking.

Data book, my friend, keeping variables isolated.

 

[KiwiShtr]

Re: Optic/Scope hot/cold affecting POI?

This mainly came to mind between shooting our first string of shots. I was shooting against BR guys who were under cover and out of the sun. I have a brake on my rifle so I relagated myself to outside the shooting shed on the ground (somehow I shoot better off the ground and my bipod than off a bench). As I was waiting for scoring, the sun came out and my scope became VERY hot to touch (forgot to put my rag over it). Then thought about what the metal was doing. Though I guess with all the heat, blinding sweat, mirage I was trying to deal with, the scope metal temp would have been the last thing to worry about.

You guys bring up some very good points. Grump, Data book inputs... very good point. Im good when it comes to some aspects but slack when it comes to others. I like your idea of isolating variables, keep apples with apples so to speak.

Theonetwo, I also like the idea of painting your wpn tan/lighter. I hadnt thought of that as a remedy/to help in heat absorbtion. Also another excuse to paint it haha. I actually asked the question (in another thread) why people with AI AW's dont paint them (either krylon or Cera/Dura/Guncote). I guess its a big call for such a pricey bang stick.

Felderthewelder, I think I know the barrel shade your talking about. Alot of BR guys use them. I was under the impression they were to keep mirage/heat from the barrel affecting sight picture through your optic? But what you say does make sence.

Thanks for your reply guys, sorry it took so long to re post back here.