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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/19/2010 at 12:49
Roy Finn View Drop Down
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On another site there is a guy who owns GreyBull Precision Rifles who is stating that thermal expansion of the riflescope itself effects the POI change in LR shooting. Huummm, a scope stretching in length enough to change your POI ? I figured we have enough scientific minds here such as with Dale Clifford, Koshkin, RifleDude and some others I'm probably missing to discuss this and possibly give this some merit or not. The owner further states that his rifle "turnkey system" has an aluminum bedding block that somehow counter acts the thermal expansion of the riflescope and this to me seems pretty far fetched to say the least. I mean really, how in the world will a aluminum bedding block attached to a steel receiver with steel mounts counter act this theory of thermal scope expansion ?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 13:10
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Given the difference of atmospheric temperature ranges, the affect of direct sunlight on a scope surface can cause the expansion of the scope to have a miniscule affect on the poi. If zeroed at 30 deg in the shade, and shooting in 100 deg in the sun. The range that would have to be shot at would need to be vastly greater than is appreciable by even the longest ranges attainable today for it to be noticeable. Add into this the human err, and how much is one versus the other is actually moot in my opinion.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 13:23
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  First off I'm not going to weed through the posts in the thread where this "discussion" is taking place. BTDT but no more!  Does he say where the heat that causes this expansion is coming from?  From the reciever?  I can't see anyone shooting enough rounds fast enough to get a receiver hot enough to affect the scope.  From the air temp?  I could see a scope getting very hot if the firearm was left in direct sunlight more so than heat from the receiver.  As far as the bedding block goes I'm guessing it is to act as a heatsink to absorb heat from the receiver and disipate it before it reaches the scope.  So I guess I may have answered my own original question.  Whacko    He's meaning the heat that affects the scope is coming from the receiver.  And just when I thought I had heard it all about adverse affects of external sources on accuracy.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 13:24
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if occurs and does it affect long range shooting, two different things. From experience the answer is no. things like a right hand shooter to pull the shot to the right, ES of the loads used (ambient air temp effect on poi changes cooling and heating of powder charge), and simple stacking error in the elevation thread pitch would have more effect. (I'm sure there are others ). Giving the benefit of doubt for a moment to the guy, it could be set up as some sort of heat sink, but if that is the case why doesn't he use copper?

Along another line but somewhat similar, I once came accross an (Handloader about 15 yrs ago) article where the guy said that bullets going to sleep and becoming more accurate at longer range was due to parallax error in the scope. This theory was interesting because it approached the problem from the optics angle rather than the pitch and yaw of projectile movement. Could this and your topic be related??, Anyway to continue I was reading a post by Litz on SH (this morning) where he brought up the optics relation to the sleep problem and was asking shooters for twist rate, gun etc. to build a data base. Does history repeat itself or what??
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 13:50
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I can't find the thread, but we had this discussion around here a few years back.
All materials change volume with changes in temperature. Steel has a lower coefficient of thermal expansion than aluminum. I believe that having the aluminum block would do the opposite in terms of reduction change.
Secondly, I hunt and would be far, far more worried about condensation regarding temperature changes than any possible deflection of material due to heat.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 14:04
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  Just looked at the prices of scrap metal so I can see where using copper rather than aluminum as a heat sink would be cost prohibitive.
  Steel may expand less than aluminum with temps being equal but aluminum absorbs and disipates heat at a quicker rate.  Hence one of the uses of aluminum over cast iron in high performance intake manifolds.  It absorbs and dispates the heat from the engine and minimizes the amount of heat reaching the fuel and carb or injection system. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 14:05
Roy Finn View Drop Down
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This guy's name is John Burns and is the owner of GreyBull Precision Rifles who is selling a "turnkey" long range system that is made up from a 700 action, match barrel, B&C stock, tactical type mounts, a Leupold scope and his own turret design that correcspondes to the round the rifle is chambered for. You only have a choice of 3 or 4 chamberings and he charges 6 grand for the setup. Anyone who has put together a similar type rifle knows there is about 2500 to maybe 3000 tops in that system with the scope. Anyway, that's not what my post is about.
 
The "thermal expansion" he's referring to is from outside temps, not barrel or receiver temps and for the life of me I cannot see how an aluminum bedding block can have any effect on what may or may not be taking place to a riflescope that's attached to mounts and a CM or stainlees action. Alot of very rigid metal between the scope and the bedding block. I'm thinking snake oil salesman more than anything else.
 
An excerpt....
 
"Think of the scope and block being an aluminum sandwich. When one expands so does the other as long as each reaches the same temp.

If you take a cool rifle and let the sun beat down on the optic you are going to see a measurable zero shift. Keep it in the shade and all the parts will stay at the same temp.

I am not claiming a necessity concerning the bedding block but merely pointing out an area where the aluminum bedding block has an advantage.

I also am doing this to show the level of experimentation that has gone into the system we sell.

No one else in the industry has ever brought this to light. I am either full of crap or maybe I obsess about ways to make bullets land on targets far away".


Edited by Roy Finn - September/19/2010 at 14:14
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 14:17
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  Outside temps?  Can't see a use for a heatsink if he's not concerned with heat from the firearm itself.  And it surely wouldn't be there for rigidity.
  Anything being mentioned about how long he's been in the business or anything on his background?  I think I'll go take a look at his web site.
 
  So he says,"Think of the scope and block being an aluminum sandwich. When one expands so does the other as long as each reaches the same temp."
  
  But as Doug pointed out they two materials don't expand the same amount when the temp is the same.
 
 


Edited by 300S&W - September/19/2010 at 14:22
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 14:21
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I think he was connected to the Best of the West guys several years ago. I have no use for those clowns.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 14:25
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 Oh.  I don't have access to cable/satellite but have read about them and their exploits.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 15:09
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DTIC, US ARL,  ABERDEEN PROVING /TESTING MDhmm hmm... have done extensive testing on this... Their is no solution to my knowledge, many many materials, alloys, and other various fabricated solutions were tested but all are subject to the thermal expansion and specific heat properties of the base metals, and or with the basic laws of thermo-dynamics unavoidable. 
The Optic cover (your eyes) is the best solution they have for this so far.
The Barrel is always the focus more than the Bedding or the Optics... 
 
I believe they came up with some silcon nitride ceramic bedding compound...
 
Kick Boxer can probably come up with something...


Edited by 338LAPUASLAP - September/19/2010 at 15:25
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 16:11
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It boggles my mind to think that a human being could hold a rifle steady enough or be a good enough shot to actually notice the difference! It would seem that projectile variance would have a greater effect. Heck, the phase of the MOON would have a greater effect! Loco Barrel heat; Sure! Big GrinBarrel/bedding block/receiver/scope mounts/scope heat? Shocked Is this even possible to the extent that a person could notice it??
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 16:20
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Looks like part of The GreyBULL name is correct at least.
 
Sure glad I'm out of the scope business and don't have to be current on all this mind boggling scientific stuff.............................
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 17:30
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Where are my after-market cooling fins? Or better yet, hydraulic cooling using your own urine.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 18:58
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Who cares when wind drift has so much more effect.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2010 at 22:21
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Sounds like another great marketing ploy to sell someone a 1000yd rifle system in a box. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 08:18
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A quick and dirty (which means there are a lot of assumptions that went into this) and I believe "worst case", calculation of the expansion coefficients of the "probable" materials (steel rings and mount, high grade aluminum alloy tube, quality glass, condition of scope being sighted in at a base temp of 72degF, rifle/scope heat soaked to 150degF) results in a possible POI change of about 1/2 inch... at 2000yards.  And, that is discounting linearity of expansion.  In the near field, the change is on the order of five10thousandths (remember that is with a 78degF change in temp from sighting in condition).  I don't know of any correction a shooter can make that will correct for that small a change.  There is thermal expansion and it does have an effect, but the effects are minimal.  If the rifle/scope were very cold and forced to heat up very quickly, the differential of expansion in the various materials might make a little more difference, but it still won't be very much and would not be "correctable" by human hands. 

I am now more confused than ever about the utility of the Greybull solution.  There is nothing that could logically be done via a bedding block that would improve the above number.  And I don't think it will matter in your overall calculation, anyway.  For one thing, unless you had some sort of instrumentation showing all the hot/cold spots, it would be almost impossible to determine the direction of change, if you COULD calculate the amount  I had to assume uniformity for most of the calculations.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 08:31
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Kickboxer,
Here is the formula you are looking for... works for me..
 
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 08:34
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Yea, what he said...Head Bang
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 08:41
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The heat flow characteristics could be calculated using partial differential equations and Finite Element analysis for the block assembly but the scope would be really difficult. Even if the bedding worked as claimed, why not get a new Savage with the same type of bedding?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 09:48
Roy Finn View Drop Down
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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.
 


Edited by Roy Finn - September/20/2010 at 09:51
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 09:54
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Based on the above post I really have to wonder what it is this guy thinks he's discovered. He heats a scope and it changes it's zero...........God only knows what takes place inside a scope when heat builds but I'm thinking it has nothing to do with the way a rifle is bedded.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 10:22
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I am always amused when an idiot like this tries to explain how a novice shooter can be a super secret squirrel sniper by simply buying his product.  Take out all the materials associated with rifle, optic, and ammunition: the novice shooter still has to provide eye sight, rifle support structure, and hammer release, and those are the variable parts that really mess up a shot.

A bad wind call at 1,000 yards and you are hell and gone from the target; rather than address that with the newbie, they talk about thermal expansion as the reason others cannot do what the buyer of this widget can do with ease.

There are crooks in every industry, selling promises no one can keep.  Just look at Counter Sniper optics.


In truth, I thought about setting up a shop like this a few years ago, not raping people on prices, just turn-key rifle/optic/ammo, decided against it, margins are too low - unless you way overcharge people and explain it away as proprietary thermal blocks and secret break-in procedures.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 10:39
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Now I am curious... Has anyone ever actually seen a change in POI due to heat?

The guy's experiment is easy to replicate. I would love to do it here, but it appears that this year in WI sun and heat are gone for the season - might have to wait until next spring:-) Is there anybody under sunnier, more southern skies who would just test that at the range?

I could see how you could get more parallax error from heat expansion. But, short of modeling the system like Kickboxer did, I am uncertain there would be a practical effect. I am not sure we need a heat flow analysis, probably a simple static linear expansion analysis would be enough.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2010 at 10:52
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The problem is attributing POI shifts to certain factors.  Over-all weapons systems absolutely have a POI shift with changes in temperature, but it is usually attributed to ambient rather than the temp of the optic or the barrel.  Hotter air is less dense, so bullets fly with less resistance; therefore every rifle should have a zero associated with each altitude in which it will be shot and each temperature range in which it will be shot.  As a barrel heats, POI can shift, but the barrel has to heat a fair amount.  (Cold barrel/cold shooter is something else - and a raging debate as well.)

Experiment control would be primary, and very difficult.

Or, one could do the shooting, not try to explain causation, and be happy that you can account for the shifts in POI.

At the end of the day, he is selling his widget, which is fine; but he is doing so in a less than honest and forthright way, which is not fine.
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