Is a scope level needed?

[Pdvdh]

You can lead a horse to water, but...

 

[Pdvdh]

The rifle can be canted to hell and back....as long as the scope is leveled from shot to shot!

That is a fact.

Lost me on this one... Why would a long range rifleman want to add an additional horizontal component to bullet trajectory (in addition to spin drift, Coriolis drift, and wind drift), by shooting with a canted rifle?

How does this work? Do you use a ballistics program that allows the option to enter rifle cant as an input entry?

And then do you determine your rifle cant and enter that value into your ballistics program in order to obtain dope for elevation and windage correction?

 

[MontanaMarine]

The bullet doesn't care if the rifle is canted, the bullet is responding to gravity.

Once the scope is leveled, it also is calibrated to gravity.

I think the point being made is that the rifle and scope don't necessarily need to be on exactly the same plane, but the scope needs to be aligned with gravity, as that is the path the bullet is going to follow.

 

[Michael Eichele]

The bullet doesn't care if the rifle is canted, the bullet is responding to gravity.

Once the scope is leveled, it also is calibrated to gravity.

The scope yes but your statement doesn't account for the fact that the mount doesn't stay directly between the bore and scope if the rifle is canted with a level scope.

The bullet also responds to angle of departure be it vertically or horizontally.

An exaggerated example would be if you mounted the scope 90 degrees to the receiver. Now assuming you're using a 0 degree base, you sight your rifle in at 100 yards with the rifle canted 90 degrees and the scope 'level'. You still use your vertical adjustment to get your elevation right. If your scope is mounted 2" from the receiver, you have to compensate by changing the angle of the scope so that the bullet would cross the line of sight to hit center. The problem is that while your scope is angled directly at your target at 0 degrees horizontally (line of sight) the barrel is not. The bullet departs the barrel at an angle not perpendicular with the target even though it strikes bullseye at your zero range. Since you scope's line of sight is zero degrees and if the bullet had exited perpendicular to the target, you hit 2" off center horizontally, hence the reason you have to adjust you windage to create a line of departure not perpendicular to the target so that your bullet will cross into the line of sight which happens to be your point of aim.

Now move your target back to 400 yards. Do you hit center of target horizontally? That's a negative. Why? Because the bullet didn't depart the barrel perpendicular to the target. It will only cross the line of sight horizontally at your zero range.

Then if you're shooting up/down hill, you interject another problem. Since the internal tube is perpendicular to the target, the main tube is not. Neither is your scope mounted level. As you angle the rifle up or down you get false readings on your level as it moves up or down. It's called the third axis.

Granted, this is an extreme case but illustrates the danger in not leveling the receiver and scope together.

 

[Pdvdh]

I was inclined to go there. Michael already has.

Here's the tough way to learn the cause and effect of canted rifle POI error.

If you truly believe the only important factor for proper rifle position is to position the vertical cross hair parallel to the force of gravity, no matter the location of the rifle bore relative to the intersection of the cross hairs, then mount your scope so its windage turret is rotated to the location the elevation turret is supposed to be located. Now shoulder your rifle while laying on flat ground on your right shoulder. This will position the elevation turret pointing toward the sky, and the windage turret toward the horizon, from the scope tube. Shoot groups at 100, 400, and 800yds, adjusting your elevation and windage turrets to the dope values calculated from your ballistics program - with no correction entered into the ballistics program for this 90-degree rifle cant. See how this 90-degree rifle cant affects POI on your targets. Ensure you have a safe background, because you'll be skipping bullets into the wild blue yonder at 400 & 800yds.

After obtaining dismal results on target, realize that the closer you get your rifle set up to zero rifle cant from this 90-degree experimental cant, the closer you'll be to eliminating this source of error (rifle cant) on your POIs.

 

[Michael Eichele]

I was inclined to go there. Michael already has.

Here's the tough way to learn the cause and effect of canted rifle POI error.

If you truly believe the only important factor for proper rifle position is to position the vertical cross hair parallel to the force of gravity, no matter the location of the rifle bore relative to the intersection of the cross hairs, then mount your scope so its windage turret is rotated to the location the elevation turret is supposed to be located. Now shoulder your rifle while laying on flat ground on your right shoulder. This will position the elevation turret pointing toward the sky, and the windage turret toward the horizon, from the scope tube. Shoot groups at 100, 400, and 800yds, adjusting your elevation and windage turrets to the dope values calculated from your ballistics program - with no correction entered into the ballistics program for this 90-degree rifle cant. See how this 90-degree rifle cant affects POI on your targets. Ensure you have a safe background, because you'll be skipping bullets into the wild blue yonder at 400 & 800yds.

After obtaining dismal results on target, realize that the closer you get your rifle set up to zero rifle cant from this 90-degree experimental cant, the closer you'll be to eliminating this source of error (rifle cant) on your POIs.

Exactly.

See illustrations below:

 

[Michael Eichele]

Second illustration:

 

[jmitchell135]

Lost me on this one... Why would a long range rifleman want to add an additional horizontal component to bullet trajectory (in addition to spin drift, Coriolis drift, and wind drift), by shooting with a canted rifle?

How does this work? Do you use a ballistics program that allows the option to enter rifle cant as an input entry?

And then do you determine your rifle cant and enter that value into your ballistics program in order to obtain dope for elevation and windage correction?

I should recall my "fact" statement as I can see the issue. I personally mount all of my scopes square to my rifle.
However.... I know of a very well renowned champion f class shooter that mounts his scope unlevel to his rifle according to the most comfortable position of the rifle when he is prone. He is able to get in the same position every single time, and his scope is level to the world.
Now I can see, just as I have a level and would argue that it is a must, that mounting the scope square to the rifle because there is no telling the position you will find yourself in.

 

[Michael Eichele]

I should recall my "fact" statement as I can see the issue. I personally mount all of my scopes square to my rifle.
However.... I know of a very well renowned champion f class shooter that mounts his scope unlevel to his rifle according to the most comfortable position of the rifle when he is prone. He is able to get in the same position every single time, and his scope is level to the world.
Now I can see, just as I have a level and would argue that it is a must, that mounting the scope square to the rifle because there is no telling the position you will find yourself in.

That is a very good point that I never thought of. That said, F-class matches offer unlimited sighters...1st round hits at some random range would become much harder., hence the reason for your last sentence. Still a very good point though.

 

[jmitchell135]

That is a very good point that I never thought of. That said, F-class matches offer unlimited sighters...1st round hits at some random range would become much harder., hence the reason for your last sentence. Still a very good point though.

Off-Set Scope Mounting Rail within AccurateShooter.com

This article is a good example of an offset scope to rifle. With a known distance and a scope level, the rifle in the article will be able to be on target even though the scope is so far offset. With an unknown distance, and as the last paragraph of the article states, if the rig gets unlevel, the offset will cause a huge problem.

Random ranges become much less random when you know your equipment and have all of the modern advancements available to us. Those which have allowed us to make the long range shots we make, but there is no doubt that they are more difficult if your scope is offset or unlevel or there is an unknown variable.

This all goes back to the importance of the scope level and the importance of knowing your gear for the long range shots.

ETA: If you don't want to read the article here is a picture.

 

[7magcreedmoor]

I have heard several Pros recommend mounting the scope with a built in cant to cancel out spin drift, which is actually an old idea. How old? I have shot a 30-40 Krag with flip up peep sight that had the spin/cant factor built into the rail that you moved the rear sight up an down on. These rifles were our issue infantry weapon during the Spanish-American War. The modern scope approach to this is to determine the amount of spin drift with your ballistic program, then using a tall target at 100 yards dial the amount of elevation you need for 1000 and twist the scope slightly in the rings until the high group is offset by the right amount on paper. I haven't done it , but I can see how it would work. Of course I STILL want my level on the rig to keep me plumb when I shoot it.

 

[MontanaMarine]

Back in a previous life I had a secondary MOS of 0341 Mortarman.

We did shoot in direct-fire mode now and then with the M29A1 81mm mortar. Talk about offset optical sight.

The fundamentals seem the same as long range riflery though. Apply the dope to the sight, and level her up.

I do have my scopes mounted square atop my rifles. But I have heard of others (David Tubb as an example) who prefer an offset.

 

[Unofficial Gun Addict (UGA)]

I'm finding it hard to believe that this thread has generated so many pages and how much 'resistance' there is to using a level.

Here is a fact:

A simple formula for how much horizontal deviation you will see:

Sine of the degree of cant * drop at desired range from boreline. Drop from boreline is NOT corrected for your zero.

Based on 0' elevation, 29.92 in. Hg. 78% humidity, 3000'sec MV, BC of .5, scope height of 2". An example would be a drop of 328" at 1000 yards (corrected for a 300 yard zero is 257").

The sine of 6 degrees is .10453

Take .10453 * 328" and you have 34.28". This is how much horizontal displacement you will have at 1000 yards with a 6 degree cant.

Vertical deviation is:

(1- cosine of cant degrees) * drop at desired range from boreline.

(1-cosine 6) = .00548

.00548 * 328 = 1.8" impact low at 1000 yards.

I said a simple formula because the reality is its a bit more complicated but this is a VERY very close approximation.

Use a level, don't use a level. The choice is yours. I know I don't want to miss by nearly 3 feet at the buck of a lifetime so you will always find a level on my rifles.

M

I guess the resistance from me is that it appears to me that most people here believe that everyone needs a level in order to mitigate cant... and my feeling is that perceptually speaking, the ability to determine vertical cant or lack thereof may differ from person to person. I mean, there have been plenty of amazing long distance shooting going on since as far back as ww2 and snipers shooting vast distances accurately and reliably without the aid of a level, or even scope for that matter. Imagine these long distance shots trying it line up iron sights to be vertically true... but it was done. Now some individuals could obviously pull this off and do it repeatably... while others obviously could not.

I'm just thinking seeing a 6* cant might be very noticeable to some! while others might not be able to tell the difference. I'm pretty sure it would stand out to me, but perhaps not under all tHe shooting conditions I'm involved in, hence I'm going to test it out and see.

 

[WildRose]

I guess the resistance from me is that it appears to me that most people here believe that everyone needs a level in order to mitigate cant... and my feeling is that perceptually speaking, the ability to determine vertical cant or lack thereof may differ from person to person. I mean, there have been plenty of amazing long distance shooting going on since as far back as ww2 and snipers shooting vast distances accurately and reliably without the aid of a level, or even scope for that matter. Imagine these long distance shots trying it line up iron sights to be vertically true... but it was done. Now some individuals could obviously pull this off and do it repeatably... while others obviously could not.

I'm just thinking seeing a 6* cant might be very noticeable to some! while others might not be able to tell the difference. I'm pretty sure it would stand out to me, but perhaps not under all tHe shooting conditions I'm involved in, hence I'm going to test it out and see.

Some people naturally have a sense/eye for plumb/level/square. A lot don't.

I do and always have, but my dedicated long range rifles all have a scope level or rail mounted level.

Cheap insurance and if you have time to double check yourself it's well worth the minimal investment and time to properly install one.