Why scope cant is important
- Thread starter ztirffritz
- Start date
There are two issues with this. Correct scope mounting is important, and too many system rely on using a bubble level. I use an Arisaka unit which I find works better. It uses a wedge arrangement, not your eyeball per se.
https://www.amazon.com/Arisaka-Optic-Leveler-Combo/dp/B00W8AXZ98/ref=sr_1_12?ie=UTF8&qid=1480434388&sr=8-12&keywords=scope+leveler
The other is rifle cant. Most folks use external levels for this which means you have to take your eye off the target. The scopes I use have internal levels, which work much better in my opinion.
https://www.amazon.com/Arisaka-Optic-Leveler-Combo/dp/B00W8AXZ98/ref=sr_1_12?ie=UTF8&qid=1480434388&sr=8-12&keywords=scope+leveler
The other is rifle cant. Most folks use external levels for this which means you have to take your eye off the target. The scopes I use have internal levels, which work much better in my opinion.
Upvote 0
The Arisaka is a great starting point for making two flat surfaces parallel, but unless those two surfaces are perpendicular to the horizon, and mutually centered left to right on the vertical/perpendicularity relationship between the bore axis and the optical center of the scope, the net effect may still leave something to be desired.
An external bubble level does one of two things, and does each very well;
An external bubble level does one of two things, and does each very well;
- Best case it assures repeatable optimal orientation
- Worst case it assures repeatable flawed orientation
Upvote 0
Here is one method used to eradicate a "flawed projectile azimuth" caused by optics perceived to be level, yet optically centered to the right or left of the bore that lay beneath them
- Shoot and zero at Distance "A"
- Double the firing distance in no wind, fire a group observing windage error (if any) measurement "B"
- Rotate scope CW if error "B" is off to the right... CCW if error "B" is off to the left, until one-half of error "B" is corrected (Call it dimension "C").
- Having a way to FIRMLY secure the rifle during scope tweaking allows non-firing adjustments, otherwise it will be necessary to adjust, fire for effect, repeat until dimension "C" is produced. Annotate that dimension. This step takes a bit of trial and error, but as long as you don't adjust ANY turrets during the process, and only loosen/tighten ring tops during the process, you should be able to sneak up on optimal scope orientation
- Return to original forward firing point "A" and fire a new group. Expect/hoping for a windage error =C/2 (off in the same direction as error "B" and "C")
- Zero windage at distance "A"
- Windage zero should now be universal and correct at ALL distances.
Upvote 0
Anybody else use the mirror method for getting the reticle perpendicular to the barrel? I've found that to be the quickest and easiest now that I have a rest for the rifle. If you haven't heard of it before, just point the rifle toward a mirror, center the reticle on the scope, then rotate the scope so that the reticle bisects the center of the barrel. The higher the magnification the better the accuracy. Some room for error here I'm sure, but it's worked well for me so far.
Upvote 0
Certainly not all, but most modern guns, including airguns, come with some sort of flat (not round) mounting surface on the top of the action. Picatinny and 11 mm dove tails are examples. And, all modern scopes with internal adjustments have the underside of their adjustment housing perpendicular to the crosshairs—an industry standard. This makes the use of the Arisaka device the method of choice. This does not address other mounting, like those made for say a Benjamin 397.
And, I agree that an ill-mounted scope's cant issues will not be addressed with an internal level. All this said, I would bet that most cant errors are a result of handling (holding?) the weapon incorrectly. For that issue, assuming the scope is correctly mounted by whatever methodology, the internal level is superior to an external one.
And, I agree that an ill-mounted scope's cant issues will not be addressed with an internal level. All this said, I would bet that most cant errors are a result of handling (holding?) the weapon incorrectly. For that issue, assuming the scope is correctly mounted by whatever methodology, the internal level is superior to an external one.
Upvote 0
To clarify, I think the video's explanation of why rifle cant is a problem is good. I have no clue about his solution for removing/preventing it.
Upvote 0
Upvote 0
jgburks,
That is an outstanding way to attain a theoretically optimal starting point.
In many if not most cases if not perfect, it will be sufficient for "government" work.
Keep in mind however, Murphy's Law may yield hidden variables
Variables include;
- Barrel yaw in action (not completely square)
- Barrel bore deviation (including manufacturing anomolies, shooter inflections, or harmonics)
- Individual(s) varying perception of true horizon (as others have noted)
Upvote 0
Distance from bore center to optical center plays a role as well.
As the distance increases between the two the effects of canting
become much worse. And the ability of the shooter to detect it
become much harder as well. Truth be told virtually everyone
is canting to some degree all the time.
The best method for ensuring your scope is at true vertical
is to aim at a plumb bob string. The only way to ( correct canting)
is extensive practice in every imaginable scenario at varying distances.
As the distance increases between the two the effects of canting
become much worse. And the ability of the shooter to detect it
become much harder as well. Truth be told virtually everyone
is canting to some degree all the time.
The best method for ensuring your scope is at true vertical
is to aim at a plumb bob string. The only way to ( correct canting)
is extensive practice in every imaginable scenario at varying distances.
Upvote 0