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Thermal Expansion, Riflescopes and POI changes ? ?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 11:16
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  Don't believe I'll be torching my scopes any time soon to test his findings!!!!!!!!!
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Heating the scope with a torch is a "non-operational test" , anyway.  Unless one was testing for the LIMITS of the system to withstand extreme temperatures, it mkes no sense.  Again, I can find no situation where the bedding block would help minimize thermal expansion of the scope itself... unless you hooked it up to a Dewar and cooled all the metal surfaces.  Then, there would be another set of non-operational problems to overcome.  The "bedding block thing" may improve the accuracy of some rifles, but it has nothing to do with thermal expansion. 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 12:15
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Smoke and mirrors.  "Look at this hand, and pay no attention to my other hand in your pocket taking all your money."

It is a way to convince the ignorant that they are getting something to superior to everything else.  I have never shot one of their rifles so cannot give first-hand details, but if it is a 700 5R in a B&C stock with a Loopy on top, $6000 seems borderline theft.  Maybe this magical bedding block is solid gold, then maybe it'd be a fair deal.  maybe.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 12:45
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Maybe his stuff is assembled by Umpa Lumpa's!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 13:38
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One of the dumber things I've read in a long time.  He calls that "testing and Engineering?"  Uh huh.

All that does is show how much your zero will move if you take a torch to your scope before your shot on the hunt.  I don't plan to do that.  By heating the scope and action to different temperatures, naturally things will happen.  They will with a steel tubed scope as well.

For 99.9% of hunting scenarios I can think of, the scope and action will be normalized to the same temp (ambient).  The only thing that should be of concern is if the differences in rates of expansion of the different materials makes any measurable difference between actual operating temps when the entire gun is normalized to that temp. 

To test this, you'd set the entire gun outside in the cold long enough for it to reach ambient then bringing it in to room temp.  Keep in mind the Leupold boresighter is not perfectly repeatable so in order to get accurate results you need to leave it on the muzzle and ensure it doesn't move at all between measurements.

It would be a lot more productive to use scopes that have accurate click values, don't have canted reticles, track well enough you don't need to turn the turret 1/2 turn past where you want it and turn it back down every time just in case it "sticks," etc, than worrying about (or trying to confuse possible customers with) such minutia.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 14:11
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A guy on one of the other forums did a test on barrel heat and POI shift. The test is a bit in reverse where the rifle was heated by leaving it in the sun. The scope was covered. So I guess there was different temp on the two systems. Scope cold, rifle +100 deg F.
He then put 20 rounds through it at a target 600 yds away and hit small steel plates.
He then took a shot at a small dot at 200 yds and was dead nutz.
No shift in POI.
So two different temps on the two parts made no diff.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 17:32
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Edited by Roy Finn - September/20/2010 at 17:35
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 18:23
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Originally posted by Roy Finn Roy Finn wrote:

I found his testing methods...
 
 
I am going to give a methodology that everyone here can use to see how much temp change can affect zero. I don’t believe any other gun maker has ever discussed the subject and I suspect many of you are skeptical of any real effect.

Equipment needed:

1. Scope mounted rifle
2. Gun cradle to securely hold the rifle
3. Bore sighter or collimator
4. Heat source, a propane torch works but it requires care not to damage your scope


Steps

1. Make sure your rifle is unloaded
2. Place in cradle and attach collimator to muzzle
3. Adjust scope to a zero reference point on collimator
4. Apply heat to optic
5. Watch zero move

The reason I am posting this is to show some of the testing and engineering that has gone into our stock and shooting system.
 
You got to love #1 under steps.!!!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 18:45
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I bet the blow torch test would make the retical move differently depending on which side you heat unevenly. I think I will volunteer to be an independent tester on his rifle scope combo. All he needs to do is send me one for free and I will test it.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 19:17
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Notice how he over-doped, then came back, classic Leupold.

Any it was a nice shot, no doubt; but many rifle/scope combos costing far less than $6000 could have made that shot.  And, no telling how many shots he missed to get the video of the one he didn't.

I''ll give him credit for a clean kill, but that doesn't make him a great shot or the rifle a tack-driver.  A broke watch is right twice a day.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 19:23
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I noticed the classic over dope also.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 20:24
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Originally posted by 8shots 8shots wrote:

A guy on one of the other forums did a test on barrel heat and POI shift. The test is a bit in reverse where the rifle was heated by leaving it in the sun. The scope was covered. So I guess there was different temp on the two systems. Scope cold, rifle +100 deg F.
He then put 20 rounds through it at a target 600 yds away and hit small steel plates.
He then took a shot at a small dot at 200 yds and was dead nutz.
No shift in POI.
So two different temps on the two parts made no diff.
8's, though there are some good indicators there, an anecdotal event like that (a set of one) does not do much good for providing data for trend analysis.  You cannot really say if there were differences induced due to the temperature differential... it doesn't have to be a large difference, and you don't know what the original "sighting in" conditions were, what the "change in the system" is due to the current configuration.  However, the original question was concerning thermal expansion of the scope itself.  Is POI changed due to thermal expansion of the scope...  The math says it exists, but is insignificant compared to the other variables contributing to POI dispersion. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/22/2010 at 21:56
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Several things I notice. Weatherby uses an aluminum bedding block in the Bell & Carlson stocks of the Accumark, and Sub-Moa Vanguards.... of course they make no mention of it being for thermal expansion of the scope. I have more fear of atmospheric conditions affecting my stock to action mating than my scope. I don't know if the bedding block helps or not, but it sure feels like a solid thing to epoxy, or fiberglass bed your action into. I have no doubt that John Burns puts his time in behind a rifle, and is probably a very good shot. That means nothing to me as far as his rifles are concerned. The thermal expansion theory of his sounds like it was thought up by Counter Sniper's engineers. I would also like to see Mr. Burns come make that shot here..... A 2 MPH wind!? We have less than 6 days a year where the wind blows less than 10 mph. A 35 mph variable gusting wind would have messed that video up pretty badly.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2010 at 21:03
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Aluminum bedding blocks and scope mounts have a Coefficient of Thermal Expansion that is 9.1-13.0 (10-6power/degree F).  Steel has a Thermal Coefficient of 5.6-6.6.  What this means in the real world is that aluminum will move twice as much as steel per degree F.  With aluminum bedding blocks and scope mounts, this movement of Aluminum at 100degrees F., could as be much as one, ten-thousandth (.00010) of an inch more than at 30 degrees F.  Steel would move half of that amount.  This commutes to 2.16 inches at 600 yards, per inch of scope mount thickness or bedding block length.  It is not negligible, although it is small.

Edited by Oldtrader3 - September/23/2010 at 21:07
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2010 at 21:47
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I understand that the scope can expand but how does the aluminum bedding block negate this or have any impact on what is taking place with the scope that is anchored to the receiver that is made from either CM or stainless.  If the gentlemen from GreyBull said that he feels that the bedding block was a more stable platform than say pillar bedding, it would have made more sense to me. Frankly, I think he's got caught up in some BS theories and is just trying to talk his way out of something that doesn't make any sense. What he said last was if you placed a heat source on the scope you could see a POI change on a collomitor through the scope. OK, fine I'll buy that. But the bedding block counter acts this somehow ? I'm calling BS on that one.

Edited by Roy Finn - September/23/2010 at 21:56
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/23/2010 at 23:21
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Originally posted by Oldtrader3 Oldtrader3 wrote:

This commutes to 2.16 inches at 600 yards, per inch of scope mount thickness or bedding block length.  It is not negligible, although it is small.

This is not correct.  This assumes the difference in length results in a perpendicular distance change between the centerline of the scope and the centerline of the bore at each ring location.

That would be the case if, for example, you had a steal base and steel ring on the front of the scope and an aluminum base and ring on the rear of the scope.  Then, any delta between the change in lengths due to an increase in temperature would push the rear of the scope perpenicularly away from the bore line, resulting in the sight alignment error you state per inch between the rings.

Of course nobody does that.  While the stackup thicknesses will differ a bit, if the base and ring and action are the same in front as they are in back any perpendicular difference will be negligible. 

The "problem" of the aluminum scope tube and steel action results in a difference in length change along their lengths, basically parallel to one another.  That would be no problem at all except for the fact they are bolted together in the front and the back.  This can result in a small amount of stress and resulting deformation between the two.  While possible, it's still just a tiny fraction of a problem compared with something that would put all that change into a perpenicular movement between the scope and the bore line.

The only affect an aluminum bedding block could have is to "stretch" the bottom of the action the same way the aluminum scope "stretches" the top of the action in such situations.  I guess that's the theory....  In any case, when you look at the relative stiffnesses between aluminum bedding blocks (which are not only aluminum, but very thin for most of the length between action screws around the mag well) and steel action makes the idea it will have any significant affect rather silly.

There are many variables which can cause a change of zero and I've always said one should try to zero (or re-check zero) in at least relatively close to the same temps as he expects to hunt in (no 100 degree zero then going hunting in 30 degrees) just in case one of these variables wants to bite you.  That's just commons sense.

But the idea an aluminum bedding block will make a rifle immune, or even significantly better and any other properly bedded rifle, or that toasting a scope with a torch is a realistic way to replicate anything that'll happen in the real world is pure salesmanship and nothing else.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 00:03
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Agreed. Besides the action is not welded to the bedding block, it is only sandwiched by two action screws.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 15:30
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Hi Guys

 

Sorry to but in on this but over on our side of the pond temperature shift is a BIG issue.

 

This mainly concerns the sport of Field Target Shooting. Those of you not familiar with this sport, it involves shooting a series of small targets 0.75” – 1.25” at varying distances.

To range on the target we use the parallax wheel which we calibrate ourselves. Lasers are not permitted.

 

We have found that the ranging alters up to 1 yard per degree C change. Thus during a competition the atmospheric temperature can change up to 20C this means 20 yards out on your ranging. As this is high precision shooting a scope with this much shift will put you out of the competition.

 

 

For hunting purposes this precision is no big problem, if you hit the clean kill area you are fine: makes no difference exactly where it lands within that area.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 16:42
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Interesting, but firstly what is the total distance you are ranging. In other words what % shift are you getting?

Secondly is the shift not due to air density changing, rather then internal scope mechanics?
 
Dialing out parallax is bringing two focal points together, so I tend to think this has more to do with air density???
 
the index of refraction usually increases with the density of the medium.
 


Edited by 8shots - September/24/2010 at 16:50
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 17:07
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If the temperature shifts more than 5C, I keep having this problem with my CounterSniper:


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 17:18
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Originally posted by BEARCAT BEARCAT wrote:

Hi Guys

 

Sorry to but in on this but over on our side of the pond temperature shift is a BIG issue.

 

This mainly concerns the sport of Field Target Shooting. Those of you not familiar with this sport, it involves shooting a series of small targets 0.75” – 1.25” at varying distances.

To range on the target we use the parallax wheel which we calibrate ourselves. Lasers are not permitted.

 

We have found that the ranging alters up to 1 yard per degree C change. Thus during a competition the atmospheric temperature can change up to 20C this means 20 yards out on your ranging. As this is high precision shooting a scope with this much shift will put you out of the competition.

 

 

For hunting purposes this precision is no big problem, if you hit the clean kill area you are fine: makes no difference exactly where it lands within that area.




Admittedly, I am just a dumb ol' Marine, but how does a 1 degree C change in atmospheric temp translate to a 1 yard deviation in ranging?

With all due respect, you're do'in it wrong.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/24/2010 at 17:56
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Originally posted by Rancid Coolaid Rancid Coolaid wrote:

Originally posted by BEARCAT BEARCAT wrote:

Hi Guys

 

Sorry to but in on this but over on our side of the pond temperature shift is a BIG issue.

 

This mainly concerns the sport of Field Target Shooting. Those of you not familiar with this sport, it involves shooting a series of small targets 0.75” – 1.25” at varying distances.

To range on the target we use the parallax wheel which we calibrate ourselves. Lasers are not permitted.

 

We have found that the ranging alters up to 1 yard per degree C change. Thus during a competition the atmospheric temperature can change up to 20C this means 20 yards out on your ranging. As this is high precision shooting a scope with this much shift will put you out of the competition.

 

 

For hunting purposes this precision is no big problem, if you hit the clean kill area you are fine: makes no difference exactly where it lands within that area.




Admittedly, I am just a dumb ol' Marine, but how does a 1 degree C change in atmospheric temp translate to a 1 yard deviation in ranging?

With all due respect, you're do'in it wrong.

This is turning into a bit of an apples-to-ribeye comparison.

F/T shooters are dealing with very high magnification scopes and very short distances to the target.  They also use airguns which have a lot of drop at the distances they shoot.

They use oversized side-focus wheels for range finding: because of the ultra shallow depth of field of their scopes, they can tell the distance to the target by the side-focus knob's position when the image is in perfect focus.

The image focus adjustment changes considerably with temperature, so their marking on the side focus wheel end up being off and the POI also ends up being off.

However, the POA most emphatically does not change with temperature.

F/T argument aside, this whole Grebull business is far more Bull, than Grey.  The guy sounds liek a snake oil salesman.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2010 at 03:15
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Quote Koshkin "
The image focus adjustment changes considerably with temperature, so their marking on the side focus wheel end up being off and the POI also ends up being off.

However, the POA most emphatically does not change with temperature."
 
This my point as above, in other words refraction changes due to density of air changing.
 
If Bearcat is correct, and if Koshkin is correct about it being on an air rifle, what is the max distance they are shooting?
75 yds? Then 20 yds on 75 yds is a heck of a variation!
But let us wait for some more clarification from Bearcat.
 
Can Bearcat clarify that the point of impact does not shift? Simply the focussing wheels calibration alters??
 
We have the same thing with using refractometers. When getting a reading we adjust it by a factor for every degree above or below the calibrated temp of 20 Deg Centigrade.


Edited by 8shots - September/25/2010 at 03:18
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2010 at 10:09
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2010 at 12:04
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Originally posted by Rancid Coolaid Rancid Coolaid wrote:

RC, you've changed, Dude...
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