Newbie question about basic physics, I guess.

Does canting my rifle to the left or right affect bullet trajectory? If not, then why is it important?

I'm not an experienced rifle shooter, but I've recently become fascinated by trying to make 2" groups from a 100-yard distance. With breath control, it's not that hard. My question is prompted by a my recent purchase of a U.S. Optics rail-mounted anti-cant device which fits to the pic rail of my AR-15 (yes, I know it's not a precision rifle, but I'm assuming the principle applies to any rifle).

So I bought the device off eBay assuming that keeping my rifle level affects the trajectory of my bullet. But I just realized that if I was to cant the rifle 90 degrees left or right, or even upside-down, the bullet still leaves the chamber and travels the barrel length until it enters the outside air. Once it enters the outside air, the bullet begins dropping because of gravity regardless of what angle the rifle was held... or so it seems to me...???

What am I missing? Just trying to understand here.

Thanks in advance.

It affects your bullet trajectory relative to your point of aim.

Just a barrel, no. But the barrel is on the same plane as your optic. If it’s canted the scope is no longer doing it’s job.


Basically the scope and the bore have to line up, level, straight up and down to shoot straight at distance.

THIS. Of course. The scope has to be doing its job from shot to shot.
Thanks... just ignore my red face. LOL!

EDIT.... NO! The trajectory is governed by velocity, drag and drift. It will affect the shit out of your point of impact though.

It will affect the point of impact but the trajectory will be the same assuming that barrel is at the same angle.

The further your sighting device is from the centerline if your barrel, the more drastic of a result canting the rifle (away from the zeroed condition) will become apparent.  

AR sighting devices have a rather large height over bore compared to most firearms, so the effect of cant on your point of impact will be noticed at shorter ranges, or more dramatically at longer ranges when compared to many other types of firearms.

Not the trajectory, just the point of impact relative to your point of aim.

Thanks everyone. I appreciate your answers.

Old topic but I’ve got to comment.  

Assmumptions. No wind.  Let’s go with a 50-200 zero.  The sight is set up and leveled properly to the rifle.  When canted the rifle is leaning so the sight is toward the right.

The line of sight and the barrel are not parallel. The barrel is tilted slightly upward compared to the line of sight. However there is zero left or right tilt. When upright and level the bullet passes up and exactly crosses the line of sight.  Up at the 50 and back down again at the 200. There is no shift in the bullets path to the left or right.  

When you can’t the rifle to the right side. The barrel is now angled towards the sight side. This will cause the trajectory of the bullet to move to that side. Resulting in a point of impact to the right on a right leaning rifle.  The lean also causes a reduction in the upward angle of the barrel.  This will cause the trajectory to be lower and result in a lower than expected point of impact.  

When shooting through those stupid boards with slots, always aim high and to the magazine side.  Upper left shoulder in our example.  

Yes, a significant amount.

This is correct.


Practical terms, you will miss long shots if your rifle is canted.

Your optic is what you use to correct for the effects of gravity.  Gravity pulls straight down.  If you align your tool for correcting for gravity in an angle that is not in line with gravity, you're going to induce inaccuracy.

Relative to you optic centerline? Yes.

at long enough distances and/or big enough rotations, you can be significantly off of your aim.

You can see the affects at 100 yards w/ a 22lr! A cheap scope level is worth every penny.

hold to the magwell

It absolutely does not affect the bullet trajectory... however, your perceived POI is going to change dramatically, depending on how much your scope is offset from vertical:



https://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/

ETA: it's really quite fascinating, especially considering lots of "tactical" classes have you shooting from non-conventional positions.

Some really interesting pics showing this effect:

https://www.riflescopelevel.com/cant-tests/

Think of two lines.  

One is your barrel bore line.  The other is your sight line whether scope or irons.   They are not parallel.  

Presuming you are aiming at a target at the same elevation the sight line is level.  The bore line is pointing upwards slightly.  Think of it as a very skinny imaginary triangle.  Your rear sight HEIGHT OVER THE BORE is your triangle base.   With no gravitational pull you wouldn’t need that triangle and could have sights in theory parallel.    BUT we do have gravity so to compensate for gravity causing the bullet to drop the barrel launches the bullet slightly upward to allow the bullet to be pulled back down by gravity to the sight line.  

That little triangle is necessary.

It all works it’s worked out if held in a non canted fashion.  When you cant your rifle your sight line is the same (disregard crosshairs not level in your view, the center point is still on the line).  With the cant, your bore line now has a horizontal component, the chamber end is grossly not under the sight line and that horizontal shift about the sight line launches the bullet to the side, the side opposite the direction that that chamber is on.   Stock toe tilted to the right, gun shoots left (and a touch low because by canting you also diminished your actual elevation compensation of the rear sight.)

Think of that triangle made up the lines to help you visualize and reason it out.   It is designed to work in the vertical plane.  If you change that you get change down range.  

That said if you know and accept the concepts shooting with a cant intentionally can work.  G. David Tubb a senior match shooter shot with a cant.  He also had an extensive data book for the gun from practice.  His scope crosshairs were level to the ground but the gun was canted to better fit his perfect and “comfortable” shooting position.  

USGI firearms manual taught when wearing a gas mask use an offset hold for canting an M16 because of gas masks interfering with gun hold.

At close ranges you won’t see much shift due to cant.  At longer ranges it is getting more apparent the farther the range is.

Simple answer, canting changes point of impact to elevation and windage adjustments to achieve the same desired results. You’d have to create a special dope= one MOA equals L0.25MOA.

The projectile out of the barrel doesn’t care if you shoot the rifle upside down. Physics will perform the same.

Oh no! You don't get off that easy...LOL