Level to gravity

Accuracy in life can be of critical importance don't you think? I mean if a person isn't accurate errors occur, errors which can have negative impact later on. Well, whether you concur or not I believe it to be so and so my reality is thus.

As a long range rifleman I understand the relevance of accuracy to the end result of sending a projectile speeding towards its target down range.

A great number of things need to concatenate for that bullet to accurately make it down range and each element needs to be performed accurately including the stages of making the ammunition [I make my own], setting up the rifle, reading the environmental factors immediately prior to making the shot and of course the actual process of taking the shot. This small collection is, of course, only a very broad list of the elements.

Each element is important and a breakdown in the process at any point will affect the eventual shot, the ability to deliver it with accuracy and within a suitable time frame.

One element that may not be apparent to many shooters is the importance of levelling the sights. When the rifle sights are not level they are considered to be canted. The word cant refers to the rifle sights not being level to gravity, not the ground or terrain the rifle is resting on, but the actual planet, to gravity. It is highly important and super-easy to solve. It is that which I will do in this post today.

A rifle resting on its bipod and butt stock on a slab of concrete may look level to the naked eye however it may not be level to a plumb line. It is this cant that causes problems when the round is sent downrange.

The image here shows shows two rifle scope turrets and two plumb lines and an arrow pointing to each. You will note the turret on the right side is off-set, that is, canted to the right, and there's a second line running off to the right. That second line shows the angle of cant and it is that error we need to correct.

This condition can exist even if the rifle is on a level surface like concrete. Moving forward I'll explain why the cant angle needs to be addressed and briefly how it makes the eventual shot inaccurate. I always intend to make these sort of posts easy to follow though so if I get too complicated, which I probably won't, hit me up on Discord and give me a slappin'!

So, we understand that the image on the left as above is the configuration we need when making a long range shot with accuracy, but what about the right side, the canted image?

In this scenario the scope's vertical adjustment path is not aligned with gravity. When the shooter inputs an adjustment to the vertical (elevation) turret of the scope that is in this condition the adjustment is not entirely vertical as it relates to gravity. With a canted scope part of that vertical adjustment ends up in the horizontal direction causing error on that plane. The operator will not get the full-intended vertical adjustment either, however that error-input would be much less than the horizontal error. The degree of error is proportional to the amount of cant and vertical adjustment. [More cant and more elevation/vertical adjustment = greater inaccuracy.

The image below shows the elevation (vertical adjustment) turret on one of my rifle systems. This is a Kahles 624i 6-24x56 scope, a high-end unit worth around $4,000 here in Australia.

So, how much does this cant affect an actual shot? The below figures should demonstrate that very clearly. The scenario assumes a .243 Winchester calibre with a 105gr Hybrid projectile at 3000fps MV (feet per second muzzle velocity - This is the speed at which the bullet exists the muzzle which is the hole at the end of the long bit of the rifle.)

OK here goes...

The following data assumes a 3 degree left cant on the rifle system. You will note the vertical error is minor when compared to the horizontal error.

It's clear to see that a small cant of 3 degrees has a massive effect on horizontal error down range. Even at 300 yards, a very easy shot, you can see a 1 inch error and then at 500 yards a 3.1 inch error which is easily enough to destroy the effectiveness of the shot. It's interesting to note that the vertical error out to 1000 yards is much smaller, under half an inch. Not great, but acceptable. It's the horizontal error that is the big problem.

Range in yards	Horizontal error	Vertical error
200	-0.4"	0.0"
300	-1.0"	0.0"
400	-1.9"	0.0"
500	-3.1"	-0.1"
700	-6.8"	-0.2"
900	-12.4"	-0.3"
1000	-16.2"	-0.4"
1200	-20.8"	-0.5"

How does the operator rectify the cant that terrain or, indeed, the shooter him/herself applies to the rifle system. Well, it's remarkably simple. One correctly installs a scope level device.

You will note on the image above that green bubble level mounted to my rifle and below another image showing a second which is mounted more towards the front. These devices are simple in their brilliance and as you have probably worked out are used as a guide to quite literally level the rifle system prior to sending a round down range.

I mentioned correctly installed above and that's critical. If a scope level is simply mounted and not levelled initially then the readings it provides will be wrong. So there is a process to correctly level them when installing, in fact theres a few different ways to do so but I always use a plumb line. I won't go into it today though.

Why do I use two? Well, in case one fails. I had one fail in a competition once. It was in Northern Territory some 3,000 kilometres away from home. The scope level came loose and turned around mid-competition and with no way to level it...Well, the table above shows what a 3 degree cant can do to a shot. I finished 17th out of 55 shooters over a two day practical-long-range event when I should have finished in the top 6. I was not well pleased. I have two mounted now as being prepared is a part of my life ethos. If both fail I hear you thinking? Well yeah, then I'm fucked.

The rear-mounted level is by Vortex and the front-mounted one is by Accuracy 1st and is a more expensive unit which, interestingly, was the one that failed. The front one is considered to be more accurate as it uses a ceramic ball inside rather than a bubble like the Vortex unit. The theory is that the size of the bubble can expand and contract with temperature and altitude and the ceramic ball will not. The ball is floated in fluid in case you were wondering. Different bubble sizes can introduce inaccuracy. The front-mounted unit also has a Tritium vial inserted in the back. Tritium is a radioactive isotope that glows constantly for around 25 years. This means in low light or night time shooting I can still see the readings on that level. Tricky huh?

Both of my scope levels are observed with my left eye as I'm a right hand shooter. A check on the scope level is the last thing I do prior to initiating my breathing and trigger-pull process. Once that check is made I simply fall into the practiced routine of breathing and trigger-pull which rolls out smoothly and without thought. A little squeeze on the trigger and it breaks sending the round down range towards its target.

If you are still here then good on you, I'm really pleased. I'm almost done so hang in there for a bit longer.

The operator could never shoot from a perfectly level position without a scope level. A target shooter may reference a structure on a range to gain a pretty close guide, a post or wall for instance, but in the field it's not so easy and who knows if those structures are even level to gravity? That's where the scope level comes into its own. Rolling terrain can trick the eye into thinking the cross hairs are level and the consequence of a shot in this condition could be disastrous. The human eye is only able to resolve cant to a degree of (+/-) 3 degrees and so the scope level is required.

So, there you have it. A very basic explanation of cant, how it can affect a rifle shot and how to mitigate it. I have purposely omitted many details and tried to keep things pretty simple. It's not because I think you're incapable of understanding it, only because I didn't want this post to be any longer than 1679 words. [Nailed it!]

Oh, just a quick word to clarify something...The scope level is mounted to the scope and the scope is mounted to the gun. Make sense? The scope needs to be levelled prior to the scope level being mounted as the cross hairs need to be perfectly aligned to gravity first. Then the scope level is mounted to also be level to gravity ensuring that both align. There's no point having a perfectly set up scope level if the scope is not also. Savvy?

I hope I made this post somewhat enjoyable and easy to follow. I'm open to questions, and of course ridicule, as its the interweb and I'm sure there's a keyboard warrior out there somewhere who got the highest score on some computer game that knows better than me. I'm always keen to get some feedback so send it. [That's a play on words as send it is what a spotter will say to a shooter when all is in readiness for the shot - See what I did there?]

Ok, I'm out. Later people.

Design and create your ideal life, don't live it by default - @galenkp

P.s. If anyone wants to hit me up on Discord: @galenkp#9209