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Bill Myers
01-01-2009, 07:31 AM
After Reading Bills post on his scope mount system with only the front portion secured to the action,I thought that i would induce a few variables into the theory,If the aluminum base can move from temperature or pressure changes enough to actually put the action into a state of binding pressure,Then when it is only attached at the front of the action & the aluminum base starts to move,it will cause a POI shift because the action can not hold it.So in reality,a shooter would be chasing his tail when trying to get through a target ,while trying to determine if he missed a condition or his point of aim moved,After all ,if the base can move enough to influence the action,it can move enough to cause a shift in zero.How much,who knows,maybe none BILL PS Please,Do not throw me in that Brair Patch BRRR Rabbitt.

DonMatzeder
01-01-2009, 07:37 AM
The base is not what is expanding. The scope tube, being alum, expands lengthwise more than the action. This forces the scope tube to bow. Put a cool gun in the sun and on a rest. Aim it at the bull and sit and watch it for about ten minutes. It won't have the cross hairs on the bull anymore but the gun is still pointing in the same direction.

Bill Myers
01-01-2009, 07:49 AM
Don,Same result,If the scope is expanding enough to put pressure on the action & you only attach the base in the front,Then the scope will bend the base because the action is not holding in in position,& by the way,I have set up my rail gun ,With 3 scopes mounted off to the left side,indoors & watched the Reticle move around the target,No heat indoorsIts not the tube a moving,its the light refraction,A Rifle will shoot higher in bright light & lower in low light conditions. BILL

DonMatzeder
01-01-2009, 08:05 AM
By placing the rings adjacent to eachother, there is no tube between the rings to expand and cause the stress/bow. Again, there is no stress on the action in this configuration, it is stress on the scope that this fixes. On a weak action, spreading the mounts can also affect poi. This is demonstrated on many of the match airguns. One of the alternative fixes for the airguns is installing a heavy bridge over the loading port of the same material as the action. This stops the action flex. The scopes will still bow if the rings are spaced apart.

B. Harvey
01-01-2009, 08:16 AM
Seeing how sensitive the little slow 22 bullets are, there seems to be many other factors as to affect your POI than a scope slowly expanding/contracting.

A Zero is only good for conditions that you Zeroed for.
Temp, baro, RH, alt. bore condition, angle, tuner setting, wind/calm etc.

In 100-200 yard centerfire, you will see much less poi change due to atmospheric conditions (minus wind), than the rimfire sees at 50 yards.

I would have to think that something like the scope expanding or contracting would get lost in the noise of all the other things that affect the POI.

As Bill stated, set the rifle on a rest and just watch the target dance around.

Our POI is determined by what we SEE.

So now you have to ask yourself, did your POI change?
Or did you aim at the wrong spot because of what you saw?

DonMatzeder
01-01-2009, 08:22 AM
I'm not talking about a dance here. I'm talking about a steady march, away from the direction that the sun is hitting the scope.

dankillough
01-01-2009, 08:37 AM
How do you prove or disprove Calfee's theory? Do you get an action, base, rings, and scope all made from the same material and mount them in the traditional manner? This would at least get the same expansion rate.
Bill, could you use your rail gun mount the 3 scopes in each of 3 different ways and see what happens?

Beau
01-01-2009, 08:53 AM
Why would the change in refraction in varying light conditions be noticeable through the scope and not to the eye? There is no doubt that a rifle will shoot higher in increased light and the effect is immediate. But I've sat at the bench on days when there are those heavy clouds moving quickly so you have a bright/overcast switch all day and not been able to detect a change in POA. But the POI is still higher. I always assumed the refraction was affecting not only the scope but also my eye so the movement was not detectable. There's the old saying "lights up, sights up" that is really related to iron sights. That seems to indicate the refraction affects the eye as well.

B. Harvey
01-01-2009, 09:01 AM
In 06, I was shooting a 1k match and for 16 of my 20 shots, the sun was behind clouds, and I was hitting on my aim point. Then for the 17th shot, the clouds broke and the sun lit the target very hard. My first thought was to hold .5 moa low, but then I thought, I've been bit by this before, so I shot that round at the same POA, and the bullet went .5 moa high, just outside the 10 ring. I then of course held the .5 moa low for my next 3 rounds and they all were centered in the 10 ring. That one shot cost me an outright range record. Instead I tied it.

Still kicking myself to this day, and that lesson will NOT be forgotten.

Beau
01-01-2009, 09:11 AM
Yes, the POI will be high. But could you actually see the scope shift? What I'm thinking, at least from what I've seen, is the refraction shift is more with me than the scope, so I can't really see it just by using the cross hairs as a reference.

tim
01-01-2009, 10:07 AM
The base is not what is expanding. The scope tube, being alum, expands lengthwise more than the action. This forces the scope tube to bow. Put a cool gun in the sun and on a rest. Aim it at the bull and sit and watch it for about ten minutes. It won't have the cross hairs on the bull anymore but the gun is still pointing in the same direction.

That's because the erector tube inside the scope is moving in relation to the outside tube, essentially like applying a click or two.

Bill Myers
01-01-2009, 10:21 AM
Dan,I have already did the test with different scope base setups & then attached a scope to the action to see if everything works together,I even shimmed the scope to put it on one end of its adjustment range & see if the scope was still stable,They need to be close to center.Gotta go,Tony Blosser & my self are heading to Piney Hill to test my new Scope base for the Turbo,One Peice,4 Degrees offset & 5 Inches long.I have one on Inezs Turbo & put on on Tonys Turbo. BILL

Carp
01-01-2009, 10:45 AM
I've seen this scope movement before and can't make heads or tails of it. I've had my gun set up on a sighter bull (ARA) with dot over dot and waited on conditions to see amount of wind deflection for a particular condition and re-looked through the scope before touching the trigger off and seen the scope dot completely off the target dot without any movement of the gun or bench. Always assumed it was atmospheric but if POI seems to always be high in sunlight and low in overcast I just don't always see the perfect fit to that. I think if I did my scores would reflect some merit to it because I am sure that I pay very, very much attention to it. The ARA 2008 Nationals would be a real indicator for me. The more and more I adjusted my hold-off low it seemed I still seemed my POI went high. Don't know what I was missing...everyone elses scores seemed to be incredible. I think these two posts about the scope mounting are very informative and hope it helps many other folks other than me.

Carp

Kent Owens
01-01-2009, 11:50 AM
Bill Myers,
First of all, glad to see your name spelled correctly! Happy New Year!
You started a very interesting thread that a lot of shooters could learn a lot from to improve their scores this coming season. I think Tim hit the nail on the head about the scope tube expanding more than the erecror tube and causing a POI shift when it goes from 70 degrees to 95 degrees during the day. Then there's the light thing, sun and shade, and which are you zeroed for? That makes a difference now, or does it. Hopefully this thread will continue in a civilized manner, and allow some folks to learn some things to improve their scores, myself included. Looking forward to seeing what knowledgeable shooters will add to the thread.

David K
01-01-2009, 02:16 PM
I've had good results with my frozen scope because its mouthed in rubber at the front mount. Most solid mounted scopes seam to move from one day to the next but that has not been the case since I made the change.:rolleyes:

tim
01-01-2009, 03:13 PM
I see lots of guys that shoot under the roof in the shade and then go clean in the direct sun, back and forth. I suspect not all scopes are prone to this but I've been told by more than one scope guy that on certain days there are a few parts moving around in there after direct sunlight heats it up real nice.
The erector tube pivots on one end, kind of like a hip joint. One of the issues with the early Leuy Comp models was the gasket on that joint and it's tendency for subtle shifts in poi. I'm assuming it will not take lots of heat to stir things up in there but it probably pays to remember moving parts are exactly that. Heat is not your friend IMHO.

Big Al
01-01-2009, 05:19 PM
Lights up, sights up! come on guys, this ain't rocket science. All of us old guys know the reason and it quite simple.

It's because the eyes see the target better and we hold closer. How many of us have noticed when the eyes start to go, the first thing we do is add more light or complain we just don't have enough light.

Sometimes we get a little to far into the fun of theorizing enough to forget the lessons we already know the answers too.

Molly
01-01-2009, 08:53 PM
Here's a mount I made a couple of years ago for my Turbo. I made it so I could use a BV20 scope bumped to 30 power. I wanted positive clicks and the use of known scope. I had a friend (Steve Wieck) who used the same sort of set up with Foster jewel type rings. I thought why not use the base with a Unertl scope. Hope the picture comes through.

Molly
01-01-2009, 09:00 PM
Here's another pic of the back of mount on my rifle. These pictures would be a little better if I didn't have to compress them for the web.

tim
01-02-2009, 08:52 PM
Lights up, sights up! come on guys, this ain't rocket science. All of us old guys know the reason and it quite simple.

It's because the eyes see the target better and we hold closer. How many of us have noticed when the eyes start to go, the first thing we do is add more light or complain we just don't have enough light.

Sometimes we get a little to far into the fun of theorizing enough to forget the lessons we already know the answers too.

Yeah that's great if you shoot BR with a reciever sight. If your using a scope you may want to go over to the centerfire section and check for the 5000 or so posts on the issue you thought you just answered.

tim
01-02-2009, 08:57 PM
Here's a mount I made a couple of years ago for my Turbo. I made it so I could use a BV20 scope bumped to 30 power. I wanted positive clicks and the use of known scope. I had a friend (Steve Wieck) who used the same sort of set up with Foster jewel type rings. I thought why not use the base with a Unertl scope. Hope the picture comes through.

That's quite a slick setup. The only problem is that unless you've got a BV20, they are bringing some serious coin for good ones. You know off hand what the scope & mounts weigh?

jGEE
01-02-2009, 09:07 PM
Does distance between scope mounts increase or decrease POI shift if something externally moves? thanks, joe

Beau
01-02-2009, 09:34 PM
Increased or decreased distance?

tim
01-02-2009, 09:36 PM
Greater the span the smaller the click [movement] value

jGEE
01-02-2009, 09:55 PM
I'm reading these scope discussions on here and learning a lot but i'm getting confused. Up to now my budget has not allowed me a nice scope, just the cheeper BSA's and the like. I have always wanted something nice, i now realize my point of impact is shifting around a bit.

I read mr. jackie freezes the nicer scopes and some are going back to micrometer Unertl type mts. Then Bill says a single mt is best. Then someone posted we have gone full circle.

That got me to thinking about the old Unertl scopes with over 12" between bases. Rimfire doesn't put much heat in the bbl. With the mounts so far apart with the Unertl type scopes i was thinking and maybe i'm wrong -with the mounts being so far apart if anything moves maybe there is less POI shift. It seems to me with a single mt a slight movement would change the POI a lot more than if the mts are far apart. What am i missing here?
have we gone full circle and did Unertal have it right?
thanks joe

Beau
01-02-2009, 10:32 PM
I guess you could think of it as if you only had one ring or to rings directly together. If the expansion and contraction of the scope puts stress on the action, the lesser span should cause less stress. That's considering stress on the action only and not stresses on the scope. You would think it would be the same way with the barrel and Unertl but Unertl bases used a spring which may keep the stress from transferring to the barrel. Unertl may have had it right, but they probably needed the span to support the big scope.

I think the POI moves in all of them when they are subjected to changes in heat and cold whether expensive or cheap. I've never tried a frozen scope but always wanted to; however, I've heard several say they do not work well for score. The scope stresses are an issue and some people are working on innovative ideas. Sooner or later one will hit something that works and then we'll all buy it.

David K
01-03-2009, 06:00 PM
I have three brackney mounted 45 power scopes and love all three. I traveled through two airports going to the world championships at Millan Italy last summer with no major changes to impact. The front mount is in hard rubber and is not affected by action stress. This is the only set up I have found that does not move alot from day to day. From what I understand the best optics are in center of scope. Freezing crosshairs places them in the center no mater if they need ajusted. The biggest change to get used to is there is no clicks and if this is something you need you will not like this setup.

Beau
01-03-2009, 06:21 PM
Do you mean there are no actual clicks, or no adjustment?

B. Harvey
01-03-2009, 06:32 PM
The Brackney does not have 'clicks', just a smooth feel when changing elevation or windage. David has, to my knowlege, only needed to adjust the POI on one or two occasions. They seem to hold same POA/POI very well.

Beau
01-03-2009, 06:43 PM
Then a shooter would not be hindered by MOA adjustments? Seems like a big advantage and a way to have a true zero.

Joe Friedrich
01-03-2009, 06:44 PM
Beau, there are two external micrometer adjustments. One for elevation and one for windage.


Joe

Molly
01-03-2009, 07:53 PM
Tim
Sorry I did not see your post about the weight till now. I know what you mean about the cost of BV 20's they do bring serious money. I already had a couple so put it to work. I can weigh it if you are serious about using it for IR 50 but I doubt it would make weight.

tim
01-03-2009, 09:07 PM
I'm reading these scope discussions on here and learning a lot but i'm getting confused. Up to now my budget has not allowed me a nice scope, just the cheeper BSA's and the like. I have always wanted something nice, i now realize my point of impact is shifting around a bit.

I read mr. jackie freezes the nicer scopes and some are going back to micrometer Unertl type mts. Then Bill says a single mt is best. Then someone posted we have gone full circle.

That got me to thinking about the old Unertl scopes with over 12" between bases. Rimfire doesn't put much heat in the bbl. With the mounts so far apart with the Unertl type scopes i was thinking and maybe i'm wrong -with the mounts being so far apart if anything moves maybe there is less POI shift. It seems to me with a single mt a slight movement would change the POI a lot more than if the mts are far apart. What am i missing here?
have we gone full circle and did Unertal have it right?
thanks joe

Joe, probably the majority of guys that shoot this use Weaver 36X with few problems. Under 4 bills new.

tim
01-03-2009, 09:13 PM
Tim
Sorry I did not see your post about the weight till now. I know what you mean about the cost of BV 20's they do bring serious money. I already had a couple so put it to work. I can weigh it if you are serious about using it for IR 50 but I doubt it would make weight.

No don't go to any trouble, I thought you might know. I'm fine with my optics now....just curious. I think for that kind of scratch, assuming you do not have one, the Leupold Comp scopes are more than enough. I never thought the 45x was really needed for rimfire but I put one that I had on a 6PPC onto my backup gun and I really do like it, picks up that subtle mirage that 36's can miss.

Molly
01-04-2009, 09:21 AM
Tim
I am curious as to your use of a 45 power to see mirage. I have never had a scope of that power. I always felt that a scope of lesser power say the 30X saw mirage "flow" a little better than my 36X. I guess I will switch them around this spring and experiment. Thanks for the tip!

tim
01-04-2009, 12:29 PM
The better optic simply allows you to pick up a subtle mirage that the 36's miss. If it's a full on boil you're going to see it with anything.

Fred J
01-04-2009, 01:26 PM
Some scope have a greater depth of field than others. Short depth of field scopes, will only pick up the mirage at a set range of focus.

B. Harvey
01-04-2009, 01:28 PM
The modifier disc that comes with the March gives more depth of field.

tim
01-04-2009, 05:18 PM
Some scope have a greater depth of field than others. Short depth of field scopes, will only pick up the mirage at a set range of focus.

If that were as simple as that then why do the March 40's pick up mirage the 36's don't ? It's depth of field and optical quality.

B. Harvey
01-04-2009, 05:52 PM
Increasing depth of field only changes how you see the mirage. The increase in depth of field make the mirage more defined, as in more readable. Without the disc it is harder to read what the mirage is telling you. Even if you can't see it the mirage is still there, and with the mirage is a condition that can affect your shot. Lack of seeing it might not make you aim differently, like it would if you could see it.

My 40X March picks up a lot less condition than the 60X, which at times makes it easier to aim, but the 40x still picks up enough to let me know a change has occured. The 60X picks up very slight changes in the sight picture, and it will actually tell you when NOT to shoot.

I have a friend that has a 45LCS and it is a great scope, but he seems to see less mirage than I do, even when I am looking through his scope.

Everyone's eyes are different, and if you have had the pleasure of shooting with a March, there is no question of it having quality optics.

tim
01-04-2009, 08:26 PM
Absolutely. The reason my 45 Leuy came off the PPC was that a March 40x went on. The ED glass is just fabulous.

BrentD
01-05-2009, 06:06 AM
That got me to thinking about the old Unertl scopes with over 12" between bases. Rimfire doesn't put much heat in the bbl. With the mounts so far apart with the Unertl type scopes i was thinking and maybe i'm wrong -with the mounts being so far apart if anything moves maybe there is less POI shift. It seems to me with a single mt a slight movement would change the POI a lot more than if the mts are far apart. What am i missing here?
have we gone full circle and did Unertal have it right?
thanks joe

joe, Standard mounting distance for Unertl scopes and similar Lyman STS or Fecker scopes is 7.25" They can be different but this usually is the correct distance to produce 0.25 MOA clicks.

I think there would be less movement with the older scopes because they would slide as they expand in the heat. The argument here seems to be that the scopes with fixed mounts are bending.

FWIW, a lot of these older scopes have steel tubes. That being the case, they would expand at the same rate as the action/barrel and thus would not be experiencing this binding/bending. If this heating issue is a big deal it would seem to be a really good argument for steel tubes of as near the same alloy as the action or barrel as possible.

The "sun up, sights up" routine seems to be in direct contradition to Beau's experience. I think what Beau describes is due to the light inducing a greater vertical component to air circulation caused by light being coverted to heat and being reflected by the ground. The upward mirage causes the target to appear higher than it really is, and hence one hits higher on the real target.

WSnyder
01-05-2009, 05:33 PM
The "sun up, sights up" routine seems to be in direct contradition to Beau's experience. I think what Beau describes is due to the light inducing a greater vertical component to air circulation caused by light being coverted to heat and being reflected by the ground. The upward mirage causes the target to appear higher than it really is, and hence one hits higher on the real target.

I was taught slightly different phrases "Suns up, bullets up" and the opposite "Suns down, bullets down". At the time I was given the same mirage explanation you give here. I was given the advice back then by a pretty good silhouette shooter, I think it was good and has worked well for me.

Sighters are really nice when allowed aren't they!