Variables,Scope mount system

B

Bill Myers

Guest
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.
 
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.
 
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
 
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.
 
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?
 
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.
 
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?
 
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.
 
Beau

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.
 
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.
 
DonMatzeder said:
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.
Click to expand...

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

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:
 
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.
 
Last edited:
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.
 
Action with mount.

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.
 

Attachments

  • scope34.jpg
    scope34.jpg
    33.2 KB · Views: 350
another pic of mount

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.
 

Attachments

  • scope36.jpg
    scope36.jpg
    24.1 KB · Views: 324
Big Al said:
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.
Click to expand...

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.
 
You must log in or register to reply here.
Back
Top