Optimal scope setup

[nervoustrigger]

Sorry, one more thing

After thinking on this some more, it occurred to me perhaps part of the difficulty is a tendency to visualize the reticle more as a physical thing inside the scope tube.  Well, it is but the way it operates is something else.  Instead try thinking of it as a projection...something of a hologram projected onto the target.

That is the manner in which our two hypothetical scopes have identical points of aim.

[bandg]

Jason, what you just said is plain silly-"the bore is fixed"?  Fixed in relation to what?  You say the scope is not fixed (each of the scopes is tilted differently) but the bore is fixed?  I described a level line of sight to make it easier to visualize the bore to scope relationship.  Neither bore nor scope is "FIXED".  Move one and the other moves because they are rigidly bolted together.  If the scope is held level, the bore(s) tilt upward.  If the bore is held level, the scopes(s) tilt downward.   Neither the bore nor the scope is "fixed" in relation to the world.  They are fixed only in relation to each other via rigid mounts.  And the line of sight and the bore line must converge as they move away from the rifle or you would never have a zero at the crosshair.  You would have a pellet flight that starts below the point of aim and falls away from it.

"The bore does not tilt upward differently for one scope versus the other scope".  Really?  Do you really believe that?  It is nonsense.  And the way I describe a level scope (the line of sight from eye to target) was only to make that easier to visualize.  I never stated anywhere anytime in any manner that the scope was fixed.  But the bore is not "fixed" either.  The line of sight can be upward, downward, left or right.  It depends on where you are standing and where your target is.  The bore is not "fixed".  The scope is not "fixed".   But they are bolted together and move together.  It is just easier if you fix one (either scope or bore, doesn't matter) MENTALLY so the change is easier to visualize. 

One last time for folks to try to visualize this.  Look at one of the horizontal lines running across the page you are viewing.  Let that represent line of sight/what the shooter sees through the scope/your aim line.  Imagine the shooters eye is at the left end of the line looking through the scope but you are standing 90 degrees to his right looking at the scene from the side.  That is the foundation of this example.   Looking through the scope, the shooter sees the target with the crosshairs directly centered.  Perfectly aimed.  But where is the bore?  You can do this with just an unmounted scope in which case there would not even be a bore to consider.  But the shooter would still see exactly the same thing when looking through the scope-the target and the crosshairs.  Now mount a rifle to that scope.  While looking through the mounted scope the shooter still sees exactly the same thing-target with crosshairs centered.  The rifle is on the left with the shooters eye and the target is at the right end of the line.  Take a straight edge and start 1" below the left end of the line (this represents a "low mount" with the scope closer to the bore) and line it up with the right end of the line.  That is how a scope must physically pair bore to line of sight in order to make a projectile hit the target.  Before Jason says it has something to do with the optics in the scope, realize that you can change the turrets to effect this tilt (internal correction), you can physically shim one end of the scope to effect this tilt (external correction), you can use adjustable mounts to effect this tilt (also external correction) or you can use a tapered mount to effect this tilt (again external correction).  It doesn't matter how the correction is done, it only matters how the LOS and the bore are made to approach each other toward the right side.  Realize that using any of the correction methods, the view through the scope from eye to target will still be exactly the same.  The example only illustrates the RELATIVE scope/LOS to bore tilt that must be present in order for the projectile to hit the target.  NOW NOW NOW move the left end of the straight edge down another inch (now it's 2 inches below the horizontal line).  This represents a "high mount" with the scope further from the bore).   While keeping the right end of the straightedge on the right end of the line, lower the left end to that new point.  Now once again the scope/LOS and the bore are pointing at the same spot on the right, the original target.  It must be so in order to hit that target.  Do the two lines slope the same?  Absolutely not.  The lower line (high mount) slopes more steeply toward the LOS than does the middle line (low mount).  The scope/LOS to bore angle is different for the two height mounts.  Neither scope nor bore is "fixed" in the world but they are attached and thus "fixed" only in relation to each other.  That's all I have to say on this.  It isn't really that complicated but one must grasp the basic concept.  I will post no more on this topic thread but will gladly respond to PM's if anyone wants to discuss it individually.  Good shooting to all.

[nervoustrigger]

Jason, what you just said is plain silly-"the bore is fixed"?  Fixed in relation to what?

It is fixed in relation to the two scopes...the two scope bodies, anyway.

Your contention is that the two scopes give a different error, thus we have to look at what happens when we adjust each scope relative to the bore.  That's why the bore is "fixed".  After all, if we had those two scopes mounted on a rifle, that's exactly what we would do.  We would sit down and zero each of them to the same range. 

If we could angle the bore independently of the two scopes, everything is not rigidly affixed...a condition which you raised yourself:

But they are bolted together and move together.

I'll concede the use of "fixed" here is weak but we seemed to be using the term in the same fashion.  Again, you were explaining the scenario where you have to angle the barrel differently to make the trajectory coincide with each of the two scopes.  We don't angle the barrel, we angle the scopes...more specifically, we angle each of their erector tubes so their reticles--their "projected" representations--align exactly to each other against the target.

And as I've been saying, if the reticles lie on top of each other, there is no way for their errors to differ.  I frankly don't understand how you can acknowledge that to be true but continue to argue that they differ.

Lastly, it's rather unbecoming to continue to call people wrong and refer to their arguments as "plain silly" and "nonsense", particularly when you find yourself in a situation where there are at least 4 knowledgeable people calmly attempting to help you understand why this is so.

[rsterne]

Lastly, it's rather unbecoming to continue to call people wrong and refer to their arguments as "plain silly" and "nonsense", particularly when you find yourself in a situation where there are at least 4 knowledgeable people calmly attempting to help you understand why this is so.

^X2, and why I dropped out of this thread.... 'nuff said.... 

Bob

[Scotchmo]

Gun-cant happens when the gravity vector no longer lies in the trajectory plane. Gravity must be part of the equation.

Gun-cant has nothing to do with the shooters viewpoint. Scope does not matter.

[Yogi]

Sorry but when I try to quote these posts it puts my comments in as part of your post.  I see what you are saying-assuming the rifle is canted.  But how about aim high but don't cant.

Space down past the last [/quote] marker.

-Y

[subscriber]

If taller scope mounts are not more cant error producing than lower scope mounts, except at certain ranges, then the inference that scope height does not matter is not true:  It matters a lot under certain conditions, and not at all, at others.

My impression is that with low velocity airguns, and loopy trajectories that require a lot of drop compensation, scope cant is easier to detect when the scope is mounted high.  Both in terms of awareness to cant while handling the airgun; and in terms of increasing the uncertainty of shot placement where the exact range is not known.

If large POI shifts only occur at cant angles that are easily noticed and avoided, then arguing which scope height is worse seems rather academic.  If cant angles really don't matter that much, then we should inform scope companies that include bubble levels with their mounts immediately of the cost saving they could realize by deleting the bubble levels.  Ditto for target shooters for whom precision matters a great deal.

I prefer low mounted open sights because their vertical POI uncertainty is much smaller between 10 and 25 yards.  With a tall scope mount zeroed at 10 yards, taking a shot at 25 yards while aiming "point blank" results in shooting high by several inches.    Sure, you could zero that scope at 25 yards, but then shooting point blank at 10 yards results in a low shot.

The same exaggerated zero errors that occur with tall scope mounts seem to come into play when severely canting a rifle.   

Rather than argue about cant errors, my advice would be to mount the scope at a height where you can get a comfortable repeatable cheek weld.  Also, to consider the "point blank" target radius you want to hit, and the span of ranges over which you want to achieve that.  If you have a reticle with multiple aim points and you know which is best for the ranges your targets of opportunity are likely to appear at, then only the cheek weld consideration matters. 

If you are aware of canting your air rifle, concentrate on avoiding it until you no longer have to think about it....
 

[Michael Loar]

suscribed

[nervoustrigger]

What you say is true about a low scope mount having a broader point blank range (PBR) at short distances...meaning the shooter does not have to be as concerned with finding the proper holdover/holdunder for shots that are close in.  The corresponding advantage to tall mounts is a broader PBR at longer distances.  Which of those is more advantageous will of course depend on the particular use of the gun.

If taller scope mounts are not more cant error producing than lower scope mounts, except at certain ranges, then the inference that scope height does not matter is not true:  It matters a lot under certain conditions, and not at all, at others.

Tall mounts do not introduce more gun cant error (i.e. tilting the gun) at any range.  Or are you referring to scope cant (scope installed incorrectly)?

[subscriber]

Thanks for clarifying the scope height effect on PBR at longer ranges, Jason.  This supports the idea of understanding what scope height does, and then factoring in one's intended use (range) in the decision.

I tried to follow the heavy duty arguments (in the legal and scientific sense) that make up the bulk of this thread.  I am not going to argue one way or the other; other than to say, for me low mounts seem to have an advantage, because unfortunately I rarely get to shoot airguns past 50 yards - or even that far.  So, what happens between 10 and 25 yards is more import to me.

Also, that despite the feeling that tall mounts produce larger cant errors for the shooting I do; that taller mounts make it easier for me to hold a true vertical because there seems to be a stronger vertical reference.  In other words, there is no real problem in need of a solution.

So, I am stating my preference, rather than making an argument why anyone who does it differently is "wrong".

[Motorhead]

As a HUNTER class FT shooter utilizing "Holdover" mount my scope LOW AS THEY CAN GO.  This has my close range dope far less range sensitive so getting the difficult close and small KZ's is easier at the expense of having more drop at further ranges.
This however is mitigated when the scope in use ( 16X ) range finds well.  DOPE is dope and if you can break clean shots your still making kills at distance.

[Scotchmo]

As a HUNTER class FT shooter utilizing "Holdover" mount my scope LOW AS THEY CAN GO.  This has my close range dope far less range sensitive so getting the difficult close and small KZ's is easier at the expense of having more drop at further ranges.
This however is mitigated when the scope in use ( 16X ) range finds well.  DOPE is dope and if you can break clean shots your still making kills at distance.

Drop is projectile as related to bore-line.

POI is impact point as related to line-of-sight.

Scope height has no affect on drop. So I would say it this way:

"...at the expense of having more drop POI change at further ranges...."

[JungleShooter]

To mount the scope higher —
or lower....?  🤔

I'd say as low as you can and still get your eye positioned in the scope's eye box.


Because:
A higher scope will give me a point blank range farther away.
A lower scope will give me a much closer PBR.


If my quarry is farther away I do have some time to range, check hold over/ turret dials.

But if my quarry is close I have no time for that and need to shoot quickly.

—>

That's why I prefer a lower scope.

Besides, it makes the gun more compact.

Matthias

[subscriber]

With that clear and precise summary, Matthias; this thread can now be locked. 

The only other thing I would add to your "more compact" remark, is that a high scope mount makes a gun feel top heavy - or just plain heavy.

[subscriber]

Do you know the difference between scope-cant and gun-cant? Your statement is true for scope-cant. But if a gun has been setup correctly, scope-cant will not exist.

This guy set up two identical scopes with quick release on a 6.5 Creedmoor.  One had the scope reticle aligned to the flat on the receiver.  The other had the vertical cross-hair aligned to a plumb line, despite the rifle being slightly canted to match the shooters comfortable hold:  youtube.com/watch?v=eCoHG23TQcY

The results may surprise you...

[Scotchmo]

Do you know the difference between scope-cant and gun-cant? Your statement is true for scope-cant. But if a gun has been setup correctly, scope-cant will not exist.

This guy set up two identical scopes with quick release on a 6.5 Creedmoor.  One had the scope reticle aligned to the flat on the receiver.  The other had the vertical cross-hair aligned to a plumb line, despite the rifle being slightly canted to match the shooters comfortable hold:  youtube.com/watch?v=eCoHG23TQcY

The results may surprise you...

At 1000yrds - not surprising. As long as the reticle was held vertical (no gun-cant), the small amount of scope-cant needed to get the rifle comfortable will be insignificant.

With airguns, we often shoot as close as 10 yards. At 10 yards, scope cant issues will be 100x as much as it is at 1000 yards. It's a function of scope_height/distance_to_target. You would not likely see the error at 1000yards, but you would at 10 yards.

Also - if you are shooting at only one distance (whether it be 10yds or 1000yds), it does not matter at all, as long as you are sighted in (elevation and windage) for that one distance.