At what temp does your scope shift ?

[chasdicapua]

It seems to me like the person who started this thread is relating the range finding shifts with their scope to the sport of Field Target. His 55 yard target limit and referencing the WFTF video in is post leads me to believe that. 

So, while in general, range estimating may not be the intended purpose (maybe it is, I don't know) of the parallax adjuster, in the sport of Field Target the parallax adjustment is absolutely intended to be used for range estimation. 

So, let's just be clear on that so that folks who may be thinking about getting into Field Target or are just getting into it don't become confused by reading this post. 

Chas

 

[pewpewfever]

Air rifles tend to be temperature sensitive too. That’s why you put it out in the sun fir a bit before shooting, sighting in. If you take it outdoors and start shooting away, you will see changes as the air chamber heats up. Mike says he’s solved that problem recently and the Thomas rifle is now immune to temp changes.

So I would suggest, unless you have a newer Thomas, don’t look at pellet drop as an indicator of scope ranging changes with temp. Instead, just have some fuzzy or coarse objects set up at known ranges and just work up wheel markings for different temps.

 

[waynebo]

As temps change the rifle itself contorts particularly if the sun hits it

 

[kaylaindy]

I saw that interview about the scope temp markings on Homeboy's rifle in

https://youtu.be/dqH6eVem9dw?t=3831

Great video. I'm going to try that out checking my scope. Thanks for sharing! -Nate

P.S. The link above skips to the full interview with Jack Harris.

 

[bettega]

Sorry to revive this thread but I'd love to get more info out there as there only has been attention paid to this on the net for the last year or so and this is a huge reason why I am going back to open sights for not just my air-weapons but my powder burners as well.

In my experience all scopes shift with temperature and the reasons are as explained above. I have never had a scope not shift on me except when used at an indoor range or for my CO2 airguns (Hammerli and QB79) which are outdoor spring/fall only guns within certain temp ranges.

Not only do the internals of the scope shift but also pieces of the rifle, stock, barrel and even the scope mounts. You get tolerance stacking and the tolerances as well as varied heat expansion or contraction can definitely change your point of impact. Also hotter temps can lead to higher velocity which means more rotational spin drift. All guns swage pellets, shot or bullets to a certain degree and so the faster the projectile moves the faster it will wobble (even if just a little) affecting point of impact.

Lastly one very important point that needs to be made is with temperature changes the shooter will also have, well, clothing changes. If you're shooting in a T-shirt the gun will be held differently than sub-zero weather with multiple layers of jacket, parka, fleece, long johns and God knows what else you keep warm and everything in between.

So there are so many factors that if you want to have fun and keep it simple you're far better off just getting rid of your scopes whether they cost $50 or $3,500. And yes I had a S&B PM-2 and didn't care for it for one of my rifles bought on a whim. Wish I had tried it, was thinking of getting into long range precision rifle many years ago but that was a bad decision, long story, didn't end up liking it. Scope was too big, too heavy, too much magnification, reticle wasn't well visible at low magnification and it had scope shift just like the cheap ones. Now I use iron sights 99% of the time and only use scopes when I know what I'm in for and sight them in every time I shoot. For some reason iron sights don't have rings and mounts that seem to change as much. While it's harder to print smaller groups, open sights give you very predictable POI's. If you can hit a man sized target at 200 yards on one range trip, you'll be able to do the same in 3 months regardless of the temp as long as your marskmanship is still up there.

Said another way why do you think all competitions allow you to sight in your gun and they always recommend before hunting you do the same? Funny to say I've never had issues with iron sights like that. Ever. POI is much more predictable. As the ranges extend your groups will never be as small as with an optic but generally while less precise shot to shot, irons are far more "accurate" as they always are in the vicinity of where you're aiming from shooting session to shooting session.

 

[azuaro]

Been noticing changes in range finding esp in hot weather. Never really occurred to me that there is such a phenomenon until I read an article in hardairmag a few months back. When the gun would suddenly shoot high or low, my initial reaction was to blame the gun or the scope not holding true. Temperature was the least of my suspect. 

Decided to wake up early one day when the temp was in the low 60s and the day would heat up to high 90s. I'm lucky to have targets in 5 yard increments to 55 yards.

I think I marked my scope wheel back last fall when it was colder (not sure at what temp though). Started to range find the 55 yard mark before the sun was fully out with temp at the low 60s. It was spot on. I then continued to range find as the day got warmer. At bet 68 and 70F, the shift occurred. The scope shifted about 5 yards more. The 55 yard was now focusing sharp at about 60 yards. It stayed this way to the high 90s.

Tried to google topics on scope shift but not too many I can find. But in the last video posted by AEAC titled "Pyramid Air Cup the Movie", an interview with the WFTF champion Jack Harris was a revelation. He has 3 sets of scope wheel marking for 3 specific temperature ranges (48F and below, 48F to 77F and 77F above). The interview is about 1 hour 10minutes into the video.

I use the inexpensive Tac Vector 10-40 scope. For temp reading I use an aquarium stick on thermometer. 

From the video interview, it seems a digital thermometer is the way to go for a more accurate reading. 

So if you have observed temperature scope shift, maybe share your experience and how you resolved it to shoot better.

My game plan now is first get a digital thermometer. Then observe at exactly temps the shift would occur with the digital reading. Will there be one or 2 shift points ? Then verify if I have to make a different holdover cheat sheet for the different shift points. Plan on shooting a pellet drop profile at 5 yard increments.

Does it sound like a sensible game plan ?





Travelbike:

First we need to differentiate scope shifts with velocity shifts...Temperature changes the velocity of your pellets, cold air is denser and your velocities will be lower, warmer-hot air has less density and your velocities will be higher, temperature also affects the air pressure in your gun and this is reflected also in the velocity...Elevation is also a factor, higher elevations means less dense air implying higher velocities.

I mention this because many shooters tend to confuse a shift in the POI and blame it on the scope while in reality it is derived from the change in velocity...Now, if your velocity or density of the air has not changed and your POI has shifted, you then have a problem with the turrets of your scope, or your range finding was deficient and your holdover was wrong. Very seldom you will find that the problem is derived from the optics which is also possible but not is high grade scopes.

Now, if temperature affected your range finding by using the parallax wheel to the side of the scope, you should understand that ALL scopes (some more than others) will have a minor shift in the range finding scale...The reasons for these are mainly optical illusions outside the scope and the discrepancy of the different thermal expansion/contraction coefficients of the metals and materials used in the range finding mechanisms: Brass, SS, Aluminum, Titanium, Plastic/synthetics, etc. all contract and expand at a different rate. Optical illusions outside the scope refer mainly to mirage even thou you don't see the waves it will be there... Heat waves exist even at close range and they tend to make us believe that objects are farther (naked eye and though the scope optics)...So if there is a shift is in the parallax you can blame it on the optics outside the scope and the thermal coefficients of the materials used in the mechanism...

Keep an eye and record at what temperature you marked your parallax wheel and verify the temperature when you noticed the shift...Good scopes should never shift if the temperatures were the same (when you marked distances and when you shot) but I have seen exceptions...One of them was a very high end Schmidt and Bender 10-50 x 60 (30 mm) that was sold as the FT scope...I bought one of these that sold for around $3,500 -3,700 US back in 2014 or so...This scope was a beauty and came equipped with all the bells and whistles but ended up being a lemon and an abomination compared to the Exceptional S&B PMII with the same power range...This FT scope shifted for any reason and for no reason and the company opted for discontinuing this model...Recently S&B launched their new version of the same scope with a 34 mm tube and it seems they corrected the problem....I have 2 S&B PMII's on my 2 impacts: A .22 carries a 5-25X and the .30 a 10-50X and both are exceptional scopes. The "PMII" models are designed for police and military use and you don't play with these markets...Exceptional repeatability, no shifts with temp changes and outstanding optics characterize S&B PM II's. 

Lastly, if the shift is derived from the turrets of your scope, you might as well use your WARRANTY and have the factory fix the problem, no high grade scope should shift with temp changes (within normal parameters of course).

Best regards,

AZ

 

[Guest]

Your choice to use iron sights in self defence and hunting scenarios is spot on. When the competition, FT in this case requires the use of a scope, learning how it works, and doesn't is absolutely necessary. Otherwise it's going to be a practice in frustration at a match. So we try different scopes and narrow down those that are easy to use and stable as possible.