Scope temperature shift fixes

[scotton]

Well, could this be a Sightron issue? I mean, here is another person claiming POI shifts due to temperature using a Sightron scope.

Don't get me wrong, I am not doubting either the OP or the poster I am replying to. It is just something I have never noticed or even considered as I found solutions that never involved the temperature of the scope. However, maybe the fact that I simply didn't consider it is also a factor. (smile)

Anyway, again, the fact that it ONLY seems to affect ranging and not windage has to make one wonder... (smile)

I don't think we are talking about POI issues, we are talking about ranging issues. So if you set your scope range marks at 50 degrees, then go out when it's 100 degrees, the marks are off on the parallax wheel. I have a scope that shifts about 10% when hot, so the mark for 10 yards is a little off and the mark for 55 yards is 4 or 5 mm off.

 

[BackStop]

I don't think we are talking about POI issues, we are talking about ranging issues. So if you set your scope range marks at 50 degrees, then go out when it's 100 degrees, the marks are off on the parallax wheel. I have a scope that shifts about 10% when hot, so the mark for 10 yards is a little off and the mark for 55 yards is 4 or 5 mm off.

I don't think we are talking about POI issues, we are talking about ranging issues. So if you set your scope range marks at 50 degrees, then go out when it's 100 degrees, the marks are off on the parallax wheel. I have a scope that shifts about 10% when hot, so the mark for 10 yards is a little off and the mark for 55 yards is 4 or 5 mm off.

POI or "ranging" it is really the same thing. If your POI changes, then your scope ranges marks are incorrect at that time. Same difference.

And as far as 50 degrees vs 100 degrees... You are obviously not a pilot. Air density affects your shots more than most people even consider.

Air is denser at lower temps which is why airplanes can take off at shorter distances in colder temps. And it also affects your shots the same way. There is more air resistance in colder temps, so you get a slightly lower POI at 50 degrees than at 100 degrees. And I won't even get into the dew point and relative humidity. The difference you quoted, 5mm is roughly 1/5 of an inch.

I am an amateur, but I have spent a lot of time in pursuit of precision. (smile)

 

[BackStop]

You are asking good questions. The issue is a ranging issue, not really a POI shift issue.

The issue is that: You ranged your tape at one temperature at 30 yards. At a new temperature, the range says 28 yards, but you are really at 30 yards! So, you shoot at a target you think is 28 yards, so you miss. You have to find your temp shift range, so that you know once you get to another temperature and it says 28 yards, you effectively have to put in the adjustments for 30 yards, because you are really sitting at 30 yards.
If you are not side focus ranging for distance, but instead using a laser range finder, you wouldn’t have the issue. You would know you are at 30 yards and make the adjustment for 30 yards and hit your target.

As I said in previous post, POI and ranging are the same thing.

I don't click for range or use "range tape". Only recently did I start to have the opportunity to shoot farther than 63 yards. Now I have a limited opportunity to shoot to at least 96 yards safely. This is using a .177 Akela tuned to ~868fps for about 28 shots with a high and low of 867 and 870fps.

I have a limited time frame to shoot, so I take up to 3 "sighting shots" to confirm my elevation. I don't click for range, only holdover.

If the wind is calm, I can hit a blade of grass at 93 yards. Of course, the wind never stays calm when I have a pesting (chipmunk) target. (chuckle)

Anyway, my point was that POI changes and "ranging" exactly the same thing.

Now let's talk about inclinations... or not... (smile)

Yeah, that get into another whole can of worms.

All my best!

 

[Sqwirl57]

As I said in previous post, POI and ranging are the same thing.

I don't click for range or use "range tape". Only recently did I start to have the opportunity to shoot farther than 63 yards. Now I have a limited opportunity to shoot to at least 96 yards safely. This is using a .177 Akela tuned to ~868fps for about 28 shots with a high and low of 867 and 870fps.

I have a limited time frame to shoot, so I take up to 3 "sighting shots" to confirm my elevation. I don't click for range, only holdover.

If the wind is calm, I can hit a blade of grass at 93 yards. Of course, the wind never stays calm when I have a pesting (chipmunk) target. (chuckle)

Anyway, my point was that POI changes and "ranging" exactly the same thing.

Now let's talk about inclinations... or not... (smile)

Yeah, that get into another whole can of worms.

All my best!

POI does not equal ranging. You don't get sighter shots on a field target course. You range with parallax (or bracketing but parallax is common) and if you're off, you miss. These shots aren't taken at known distances and with a 12ftlb gun it matters quite a bit how accurately you range your target. If its off 5mm (or 1/5" as you said) on the parallax wheel at 50yds, you would be ranging the target at either 45 or 55yards which is upwards of a 2.5 MOA difference in hold. Thats a problem on a target thats only 3 MOA and even more so if there is wind in play, which there usually is.

We all know about incline and weather variables fyi. You should see some of the dope cards people use on a course.

 

[scotton]

As I said in previous post, POI and ranging are the same thing.

I don't click for range or use "range tape". Only recently did I start to have the opportunity to shoot farther than 63 yards. Now I have a limited opportunity to shoot to at least 96 yards safely. This is using a .177 Akela tuned to ~868fps for about 28 shots with a high and low of 867 and 870fps.

I have a limited time frame to shoot, so I take up to 3 "sighting shots" to confirm my elevation. I don't click for range, only holdover.

If the wind is calm, I can hit a blade of grass at 93 yards. Of course, the wind never stays calm when I have a pesting (chipmunk) target. (chuckle)

Anyway, my point was that POI changes and "ranging" exactly the same thing.

Now let's talk about inclinations... or not... (smile)

Yeah, that get into another whole can of worms.

All my best!

We are going to have to agree to disagree here. POI and ranging are absolutely not the same thing. How can you have a POI issue before you fire a shot? If you have a laser rangefinder that shifts 10% when it gets over 90 degrees, is that a POI issue?

This is a field target issue (which is why it's in the field target forum) that has to do with using your parallax to range find. We are all aware of temperature shift causing POI issues, especially with springers. Again, that isn't what we are talking about here.

 

[BackStop]

Let me apologize. I take "sighter" shots when I am shooting at ~93 yards.

From 10 to 63 yards, I know my hold overs and since I know my velocity within 5fps or better for ~28 shots...

Well, I think I might do OK in FT. My kill zone is .33" and my PBR is ~22-44 yards.

Until recently, all my shooting/pesting (last 6 years) was much lower power. Not exactly 12fpe, but close shooting out to 63 yards. So, I don't see a huge transition for me shooting 12fpe. I only recently purchased a laser range finder and found that my eyeball estimates were very close. Even the range finder is +/-1 yard.

I completely understand about that first shot. That is why I will never own another regulated gun. I would rather have a sweet spot that I can count on than depend on a regulator that WILL fail.

Yes, we will have to agree to disagree.

 

[Smok3y]

As I said in previous post, POI and ranging are the same thing.

I don't click for range or use "range tape". Only recently did I start to have the opportunity to shoot farther than 63 yards. Now I have a limited opportunity to shoot to at least 96 yards safely. This is using a .177 Akela tuned to ~868fps for about 28 shots with a high and low of 867 and 870fps.

I have a limited time frame to shoot, so I take up to 3 "sighting shots" to confirm my elevation. I don't click for range, only holdover.

If the wind is calm, I can hit a blade of grass at 93 yards. Of course, the wind never stays calm when I have a pesting (chipmunk) target. (chuckle)

Anyway, my point was that POI changes and "ranging" exactly the same thing.

Now let's talk about inclinations... or not... (smile)

Yeah, that get into another whole can of worms.

All my best!

I will have to disagree too. When your clicks are the same and you sit at the same distance, the temperature is not affecting the scope in a way that is changing your POI. The shot actually goes in the same place. The problem is that your ranging changes so you only aim for 8 clicks instead of 10, so you missed. If you had clicked 10 for the correct yardage you are sitting at, your POI would be correct. Your point of aim was wrong for the correct distance, so then your shot went where you aimed which was incorrect.

 

[drsquall]

I will disagree as well. It's a field target issue when ranging. If we could walk our shots in that's totally different. And regs do fail but a regulated gun is more consistent.

 

[Cloud9AG]

The issue is that: You ranged your tape at one temperature at 30 yards. At a new temperature, the range says 28 yards, but you are really at 30 yards! So, you shoot at a target you think is 28 yards, so you miss. You have to find your temp shift range, so that you know once you get to another temperature and it says 28 yards, you effectively have to put in the adjustments for 30 yards, because you are really sitting at 30 yards.
If you are not side focus ranging for distance, but instead using a laser range finder, you wouldn’t have the issue. You would know you are at 30 yards and make the adjustment for 30 yards and hit your target.

@Smok3y has the correct description of the root cause.
@drsquall you need a pointer for hotter temps and cooler temps or just remember to add +n clicks above XXF temperature. I just remember to add clicks.

 

[scotton]

@Smok3y has the correct description of the root cause.
@drsquall you need a pointer for hotter temps and cooler temps or just remember to add +n clicks above XXF temperature. I just remember to add clicks.

Or, now that you are a ScopeKnob expert, you can add extra lines to your wheel tape, blue for cold and red for hot.

 

[steve123]

Thankfully I don't hassle with using a scope to range with anymore/Freestyle/Unlimited.

Hmmm but how did I win 5 or so state matches never taking any of this into consideration when I shot in Open division in Arizona I'll never know???

 

[Sqwirl57]

Thankfully I don't hassle with using a scope to range with anymore/Freestyle/Unlimited.

Hmmm but how did I win 5 or so state matches never taking any of this into consideration when I shot in Open division in Arizona I'll never know???

Is this a rhetorical question or do you want an honest thought on why it didn't matter so much for you?

 

[steve123]

Is this a rhetorical question or do you want an honest thought on why it didn't matter so much for you?

It's a honest internal question of mine.
The why's
Because I'm not a especially good shot.
Also foremost the mental mistakes and getting the wind wrong were the main reasons why I missed.
I used the old B&L 6-24 or 8-32 and also a 40x Leupold to range with.
And I never compensated for temps with my scope. Some other national champs had their temp tapes, ect, when they came here to shoot a state match.
Also as we all know its the positional stages that most often determine the winner.

Maybe Sightrons are really that sensitive to temps but I wouldn't know because I only had one for a few days which was sent back.

But feel free to say whats on your mind.

 

[Sqwirl57]

It's a honest internal question of mine.
The why's
Because I'm not a especially good shot.
Also foremost the mental mistakes and getting the wind wrong were the main reasons why I missed.
I used the old B&L 6-24 or 8-32 and also a 40x Leupold to range with.
And I never compensated for temps with my scope. Some other national champs had their temp tapes, ect, when they came here to shoot a state match.
Also as we all know its the positional stages that most often determine the winner.

Maybe Sightrons are really that sensitive to temps but I wouldn't know because I only had one for a few days which was sent back.

But feel free to say whats on your mind.

Well I think it just boils down to a few things:

A) You're a good shooter who understands and excells at the key points of field target. Stability, holds, wind reading, etc

B) You said Open Class so I'm assuming a 20ftlb PCP? Ranging is important but let's be real, its not really THAT important at that power level. Being off a few yards on the higher end won't make a huge difference and you really aren't going to be that far off on the closer end. You've also got a pretty wide point blank range which really negates the problem from 20-40yds or so.

C) This is WILD speculation because I've never been to Arizona so I'm basing this on what I've seen on TV

Arizona is basically hot and without shade. By the time you leave the practice range your scope is up to temperture. All the shift has basically happened already and unless its given time to cool off out of the sun, shouldn't shift back.

 

[John "spysir" Blount]

Just for clarity when I said "fish tank like" I did mean " Medical Temp Strips" a search shows they cost about $10.00 for a bunch.
john

 

[steve123]

Well I think it just boils down to a few things:

A) You're a good shooter who understands and excells at the key points of field target. Stability, holds, wind reading, etc

B) You said Open Class so I'm assuming a 20ftlb PCP? Ranging is important but let's be real, its not really THAT important at that power level. Being off a few yards on the higher end won't make a huge difference and you really aren't going to be that far off on the closer end. You've also got a pretty wide point blank range which really negates the problem from 20-40yds or so.

C) This is WILD speculation because I've never been to Arizona so I'm basing this on what I've seen on TV

Arizona is basically hot and without shade. By the time you leave the practice range your scope is up to temperture. All the shift has basically happened already and unless its given time to cool off out of the sun, shouldn't shift back.

Yes 20 fpe.

I suppose I can see your point with WFTF and 12 fpe. That I couldn't comment on since I've never shot in this division.

Where the state matches were held most of the time there are a bunch of shady spots as well as in full sun because we shoot in the poderosa's and oaks. When I started setting up the courses I got in trouble a few times for not making sure most of the lanes were in the shade of the trees. Even still the sun is always making its arc so the shade is fleeting.

Come to think of it there is a home advantage thing.....

 

[cavedweller]

I will disagree as well. It's a field target issue when ranging. If we could walk our shots in that's totally different. And regs do fail but a regulated gun is more consistent.

Compensating For Riflescope Temperature Shift In FT Competition

In Field Target matches, ranging with the scope’s parallax is critical to hitting the kill zone. Riflescope temperature shift can cause big problems!

hardairmagazine.com

 

[drsquall]

Compensating For Riflescope Temperature Shift In FT Competition

In Field Target matches, ranging with the scope’s parallax is critical to hitting the kill zone. Riflescope temperature shift can cause big problems!

hardairmagazine.com

Thanks

 

[drsquall]

POI does not equal ranging. You don't get sighter shots on a field target course. You range with parallax (or bracketing but parallax is common) and if you're off, you miss. These shots aren't taken at known distances and with a 12ftlb gun it matters quite a bit how accurately you range your target. If its off 5mm (or 1/5" as you said) on the parallax wheel at 50yds, you would be ranging the target at either 45 or 55yards which is upwards of a 2.5 MOA difference in hold. Thats a problem on a target thats only 3 MOA and even more so if there is wind in play, which there usually is.

We all know about incline and weather variables fyi. You should see some of the dope cards people use on a course.

Nailed it!

 

[OkAirgunner]

I use a Sightron now but started with a BSA Platinum. The Sightron has temperature shift in the parallax knob affecting ranging. I resolved this with Plumbers Teflon tape under the rear ring. I shot in a match that when I left the hotel my car was covered in ice but with my tape did not have issues. Now for the BSA I had POI shift, I would get everything zeroed in before the match on my TX200 and after 5 lanes I would miss the entire faceplate at the farther targets. I would go back to the sight in range and find that at 25 yards I was 3" to the right. the turret springs had just given up. I have searched for someone to fix it but to no avail. The purpose for was to show that a scope can have two different issues one affecting ranging and one affecting POI.