Scope bubble levels; purpose, use, and selection

When trying to land a bullet on a golfball at 200 yards, especially with a rimfire rifle, you need as many variables as possible to be in your favor. Will a scope that is level with the rifle base insure your success? No. The scope not only needs to be level with the base on the rifle, it needs the reticle to be level with the horizon as well.

To attain the utmost in long range rifle accuracy, the horizontal cross hair of the reticle must be level with the horizon and the rifle base to allow the vertical cross hair to be truly in alignment with the actual flight path of the bullet.

A misaligned scope with 3 degrees of error can cause a perfect shot to miss the target by as much as 24 inches at 1000 yards depending on load, caliber, and several other variables. In order to successfully shoot long range, yes, a scope bubble level is an important tool.

What is rifle cant ?

Rifle cant occurs when the rifle and scope crosshairs are tilted (or canted) an not level with the horizon. Just a small amount of cant can cause an error in point of impact even though the scope is mounted correctly in relation to the rifle. The longer the distance, the larger the error.

Confusion around the scope being level

I have seen many people spend all of their scope set up time with a level on the top turret of their scope during rifle set up thinking this is what a level scope means. Then they can’t figure out why their shot seems to migrate to one side of the target at longer ranges and more and more windage has to be used the longer the distance.

It is because their reticle is not level with the horizon. It may be level with the top turret on the scope, or the scope base, but that is not the only goal of proper scope set up.

Most scope companies have a manufacturing specification of around 3 degrees max. That means the horizontal, and therefore the vertical cross hair can be as much as 3 degrees off from exact level. If it meets this requirement they deem the scope to be ready for the market.

The very top line of manufacturers can have a spec as tight as 1 degree off. This works for most people at most ranges. Not for us as long range shooters. Our goal is to be dead on …..first shot if possible, but at a minimum, at least within three shots.

How much POI error can be caused by canting the scope ?

The illustration below is from Accurateshooter.com and does a great job of showing the effect of rifle cant at even a short distance of 50 yards. You can see that the group on the right is marked 0 degrees. This is with the rifle level when the shot was taken.

The second group on the left was fired with the rifle canted to 20 degrees from horizon level. Now this amount of cant is an exaggeration but the point of impact moved significantly……..at only 50 yards.

You would never realistically have this much error because it is so obvious even to the eye but just imagine how much you could be off at 100, 500, 1000 yards.

How do we keep our reticles and rifle level with the horizon?

We accomplish the complete leveling of the rifle and scope on every shot through the use of a scope leveling bubble. Verifying the position of the bubble immediately before every shot will improve consistency which is the secret to accuracy.

Since I am right handed, the bubble level I use is readable from the left hand side of the rifle to allow me to read it while in the shooting position with a full cheek weld. The mounting band is very stable yet narrow enough to fit between the turrets and magnification adjustment which allows it to work with almost any scope / rifle combination.

All it takes is to check the scope mounted level right before the shot is taken and make sure the bubble is centered. Not only will this improve consistency from shot to shot, but also from day to day.

Which bubble level should you use ?

When purchasing a level you have to be careful to buy one where the band has room to mount to the scope with the scope rings installed. Excessively wide scope rings will not allow room for some bubble levels depending on the scope but you won’t have that problem with this one.

Vortex Lo Pro

I have these on several of my scopes. They allow you to move scopes from rifle to rifle more easily. Just level up the to the base, then make sure the bubble level is correct simultaneously, tighten it down, and your ready for business. Of course you will still need to re zero.

As mentioned above, because of the thin mounting ring, it will accommodate more scopes than any other by being to fit in the best spot between the scope rings and scope adjustment knobs.

Make sure when you are making your purchase that you select the right diameter for your scope tube.


Knights Armament base mounted level

I really like this one. It mounts to the scope base and is viewed by looking underneath the optic. It has a very low profile to make this possible but you must have the right rings for it to work properly.

It’s construction is very solid and light. Made of solid aluminum. The bubble is very well protected making it harder to break with rough handling.

One big advantage is there is nothing protruding from the profile of the rifle that can bump or get hung on things when being use in the field.
The bubble is solidly mounted in the frame to ensure no error.


Wheeler anti cant device

This one also attaches to the scope base or any picatinny rail but allows an easy side view that be seen while adressing the target without moving your head. It is the perfect application when faster, accurate shots, are needed at long range.

The bubble will fold in when not in use to prevent bumping or hanging on vegetation while in the field and solidly machined to the pin size preventing any error from wobble

I own all of the bubble levels discussed above and have them installed on various rifles. I have put them all to the test and have been satisfied with the performance. That is why I am recommending them to you. Give them a try, you won’t be disappointed.


How hard are bubble levels to install on the scope

Its a very simple process but does take a little time. It involves leveling your rifle in a rest that will hold it in a fixed position. Then aligning the vertical crosshair in the scope with a string hanging vertical at 25 to 50 yards. See more detail for the entire procedure here.

The easiest to install is the Wheeler Anti Cant Indicator for pic rails that doesn’t install on the scope at all. It actually attaches to the scope base or pic rail on your receiver and stays there permanently.

At times, scope set up an seem like you are trying to juggle 6 balls. You are using 3 levels and trying to get them all level at the same time while you tighten rings, etc. With the Wheeler mentioned above is in place it removes the worry of having to make sure it sits perfectly on the base and then is level.

But It’s not just a tool for installation or set up, it’s a shooting tool as well. This makes it much easier to perfectly level the rifle and scope during set up. Check it out here at Amazon.

Related Articles

Conclusion

If you love long range shooting and want to take your hit rate to a new level, properly install a bubble level on your rifle and you will be pleasantly surprised at what you can do an how much easier accurate shooting becomes.