Rifle cant

[RetiredArmy]

I cant my rifle when I shoot. Starting to shoot at longer range (for me) 600 yds or so. My question is should i just plumb my scope cross hair to my cant and use a scope level? I do not compete. I shoot from a bench and prone. All shooting is done from bipods and sand bags. Not interested in changing my rifle hold.
Thanks Bill

 

[Richard Coody]

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

 

[FatBoy]

I have shot with a slight cant with scopes and found no difference at 1k as long as my crosshairs were plumb on targets scope is set up with a level and plumb bob. I haven't tried it with irons as I can't wrap my head around the front end rear sights not being in the same verticle plane. I have see guys do it, but AI don't know if they have to dial windage different or not.

 

[jr600yd]

It doesn’t make a difference if the rifle is canted or not as long as the scope reticle is level. A scope level is a good idea. This doesn’t work with iron sights since the rear sight is attached to the receiver

 

[nicholst55]

David Tubb cants his rifle(s), but he adjusts the sights/scopes so they are level with his cant. It seems to work for him.

 

[370bc]

David Tubb cants his rifle(s), but he adjusts the sights/scopes so they are level with his cant. It seems to work for him.

What he said. Get the rifle comfortable for you, while you are aiming in a comfortable position, with the stock in it's natural position in your shoulder pocket, at the target that has been plumed. Then set scope level. Always after that, when the level is plumb, then you crosshairs will also be plumed. It was confusing to me at first, but Mr. Tubb cleared things up. It's what he does.

 

[watercam]

I shoot with a cant AND irons. Never did change the plane of the sights, simply adjusted for windage and elevation on the angle of the sights. It is only 10-15º so it is not huge.
Tubb used to do the same thing until he came up with his rifle system. I could as well but my hold comes up good most of the time the when it doesn't it is all me.

 

[Bart B.]

Before Dave Tubb got his system, folks used this Tompkins front sight on a barrel band. A spirit level on the rear sight windage arm showed when the rear sight and rifle was level. Front band was twisted until the front sight bubble was centered.



Some marked the front sight for the amount of cant to move bullet windage impact 1 MOA at 1000.

Looked like this on target.

 

[JMayo]

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

I don't have enough experience to know this with my rifle but it is the way my arrows go with my bow. Canting actually causes a crossing of the centerline with gravity making the fall of the rise go not to the poa. I know what I'm trying to say ! Goes to "I can explain it...but I can't make you understand" !

 

[Bart B.]

Some 22 rimfire smallbore competitors mount their sights at a 30 degree angle to the rifle so the 10 to 4 o'clock shot stringing from cross winds is automatically compensated for in windage. Happens to a much lesser degree with high power rifle ammo. This is with a right hand rifling twist. It's 8 to 2 o'clock with left hand twist 22 rimfires.

Here's the best article on this issue.....and an admission by Sierra Bullets their published article on this phenomenon was incorrect. It downloads as an Adobe Reader .pdf file.

https://www.google.com/url?sa=t&sou...FjAAegQIBhAB&usg=AOvVaw0eLZxyTONZD0SbvFW3mPAu

It's simple to calculate horizontal error at target range. Bullet drop times sine of cant angle. 300 inch drop at 1000 yards times sine of 1 degree (.0174) equals 5.24 inches.

I shoot with a cant AND irons. Never did change the plane of the sights, simply adjusted for windage and elevation on the angle of the sights. It is only 10-15º so it is not huge.

A 10 degree cant is huge. It moves bullet horizontal impact 20% of bullet drop. 26% for a 15 degree cant.

 

[RetiredArmy]

Sorry my confusion. If my rifle is shouldered at my natural cant, scope mounted so vert cross hair is plumbed straight,tightened down, then scope level mounted level ensuring my cant stays pretty much the same for all shots. Will this keep me close?
Thanks Bill

 

[Bart B.]

Sorry my confusion. If my rifle is shouldered at my natural cant, scope mounted so vert cross hair is plumbed straight,tightened down, then scope level mounted level ensuring my cant stays pretty much the same for all shots. Will this keep me close?
Thanks Bill

Yes, if range never changes.

Remember the formula.

 

[Shawnba67]

Yes, if range never changes.

Remember the formula.

Hes canting the whole rifle, reticle is Plumb. Wouldnt the only "error" come from the extremely slight off bore center of the scope hieght?

 

[Bart B.]

Hes canting the whole rifle, reticle is Plumb. Wouldnt the only "error" come from the extremely slight off bore center of the scope hieght?

No; read post 10.

If the bullets drop 3 inches/moa at 100 yards, a 10 degree cant needs a .6 inch/moa windage correction. 3 X .2 (sine of 10 degrees) equals .6.

If the same bullet drops 120 inches at 600 yards, 120 X .2 equals 60 inches. That's a 10 moa windage correction at 600 yards. The rifle barrel has to point 9.4 moa further to the side from where it pointed to zero at 100.

At 1000, bullet drop is about 450 inches. Do the math for a 10 degree cant to see windage correction numbers.

 

[jbmarshtx]

I think you're missing something in your math and the cant/scope offset calculation. Are you taking the zero distance into account?

I get a windage correction of 3 inches at 1000 yards based on a 10 degree cant, 2" scope to bore height, and a 100 yard zero.

 

[Bart B.]

I think you're missing something in your math and the cant/scope offset calculation. Are you taking the zero distance into account?

I get a windage correction of 3 inches at 1000 yards based on a 10 degree cant, 2" scope to bore height, and a 100 yard zero.

Read post #1 in:

http://forum.accurateshooter.com/th...ing-rifles-and-bullet-impact-changes.3922647/

 

[RetiredArmy]

Bart,
it sounds like it would be best if I level the rifle, then level the cross hair to the rifle then level the scope level to all of it and use it as a training aid to correct my hold(cant). I'm not being a wise guy here just trying to figure out what is the correct way to become a better shooter. Guess a tall target test is in order to verifie that vertical stays true when I dial up for elevation. Thanks for everyone's input.
Thanks Bill

 

[Bart B.]

Bart,
it sounds like it would be best if I level the rifle, then level the cross hair to the rifle then level the scope level to all of it and use it as a training aid to correct my hold(cant). I'm not being a wise guy here just trying to figure out what is the correct way to become a better shooter. Guess a tall target test is in order to verifie that vertical stays true when I dial up for elevation. Thanks for everyone's input.
Thanks Bill

Now you're thinking and going to do all the right stuff.

It's a wise way to plan then do that. Sometimes being a wise man is good.

There's a way to tall target test without shooting. Put a collimator in the muzzle, zero the scope on it, then see if the vertical reticle wire tracks its center reference from limit to limit in scope elevation.

Or solid clamp the rifle, boresight the scope where the bore points then see if the scope vertical wire tracks the barrel boresight point in elevation.

 

[spife7980]

Canting the rifle to your natural hold and adjusting your scope to level will be better than having it perfectly level and then canting it to fit your body. Obviously its best if everything is level and for benchrest theres no reason to not have it so but but I can tell you that my shoulder isnt level and I dont always shoot off of a level bench...

 

[Bart B.]

Canting the rifle to your natural hold and adjusting your scope to level will be better than having it perfectly level and then canting it to fit your body.

Both ways allow a zero at only one range. That's the compromise one has to make to do either.

Both ways have the bore axis under the scope some amount to the side of the vertical plane through the scope. If the under-scope bore-axis is to the left of a vertical plane of the scope and zeroed at 100 yards, bullets will strike that distance to the right from point of aim at 200 yards.

Taking to extreme, canting the rifle 90 degrees left with a scope height above bore of 2 inches, zeroing the rifle at 100 yards will print bullets 2 inches left at 200 yards; it started out 2 inches to the right of line of sight. At 300 yards, 4 inches left. And 2 more inches every 100 yards thereafter. The horizontal 2 MOA angle between LOS and LOF is fixed. The scope's windage knob now acts as an elevation knob to point the bullet's exit at the muzzle to a point above point of aim equal to bullet drop. The elevation adjustment moves the LOF left 2 inches/MOA at 100 yards had the scope been boresighted at infinity.

If the scope is twisted to keep it oriented normally as the rifle is canted either side to 90 degrees, the line of sight still has to change the same amounts and angles to zero at 100 yards. When the LOS starts out any amount to the side of line of fire, the bullet will be that far on the other side of LOS at twice the zeroed range.

It's another trigonometry function. Start the bullet out directly under the scope and windage zero setting on the scope stays fixed. Bullets drop only vertically.

Hope I figured this out and explained it easy to understand.