Scope mindgames (cant)

[mcoulter]

After 5+ years of shooting in my backyard, I finally took a few minutes to hang a string to verify what "vertical" is. 

I was absolutely ASTOUNDED with how far off I have been!   

Setting the stage - I shoot across my back yard with the high-side being to my right and the yard slopes down to my left.  And I have typically installed and aligned my scope indoors where I can focus on something reasonably vertical.  Like everyone else, when I brought my rifle outside (be it my back yard, the range, etc...) I would always be conscious about avoiding cant.  (Or at least I thought I was!)

After setting out my vertical string (which was just a chalk line hung from a step stool) I tried to level my rifle.  Now totally I see the full value of having a real bubble level mounted to your rifle - because I don't have one and I found that it's pretty darn hard finding any place where I could set my small bubble level.  I settled on testing two places: on top of my scope mount (which is flat) and on top of my scope turret.  I figured if these two "agreed" on what level is, I would be in reasonably good shape.  Oh, I should also mention that I have a few levels and they were all pretty consistent in their readings.  Next, I would focus on my plumb line downrange at 50 yards. 

When I did this for the 1st time and looked at the alignment I thought something was really wrong.  To my eye the setup (scope reticle and rifle) were rotated pretty drastically to the right (clockwise). 

This is what it looked like to me from behind the rifle:




But when I rotate the image to square it up (I presumably wasn't holding the camera level) it checks out:





And what was double-interesting was having a friend come over to shoot and his scope experience / perception was EXACTLY the same!   

So the take away for me is to NOT trust my own perception of vertical or level when behind the rifle!

[Matchstickshooter]

That stuff of leveling the rifle,and then putting a level on the scope just doesn't do it for me. I can make them level, on the bench,but then when I throw them up to my shoulder everything's off.
 The stock fits that little hollow, on me; between shoulder and ribs but South of my collarbone, it's how I've always shot. I hold the gun up the way that comes natural to me,and then level it.
 It's always "right there"  when I shoot.    JMHO

[Kailua]

There's a thread in "Optics, Range estimation & related subjects" on scope cant.  It shows how to align the scope to the bore. https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0
Once set I would get a scope bubble level and set it with using the a plumb line.  JMO

[nervoustrigger]

Yeah, it's pretty humbling to realize how poor our perception of level can be.  Surely the surrounding terrain at the time has a substantial influence.
 
For what it's worth, after using a scope-mounted level [that's properly leveled/plumbed to the muzzle] for a few years, I now do a much better job of holding level.  Nowadays when I'm about to pull the trigger and realize I haven't checked the level, I'm surprised that I'm usually very, very close...even if I've just picked up the rifle for the first time in a week.  So I assume it is something that can be learned.
 
Oh and just a general note regarding selecting a level, one that attaches to the dovetail is not particularly useful.  Where the scope ends up in relation to the muzzle is what matters.  You want to rotate the scope until the vertical bar of the reticle is in line with the muzzle and then lock it down.  Viewing your reflection in a mirror through the scope, that's when the reticle bisects both the muzzle and objective bell.  From then on, your hold needs to keep the reticle level/plumb, and that will often result in the dovetail being slightly canted in comparison.  So if your level is on the dovetail, it's leveling against the wrong thing.  Instead, putting the level on the scope tube allows you to adjust it to where it shows level when the reticle is level or plumb.  Now you can be assured the pellet will "rise" and fall in line with the force of gravity.

[Dairyboy]

Yeah I always thought what I was doing was pretty level until I started learning about this can't stuff and wow I've been wrong for awhile. I do just as Jason has said and aligned the scope reticle to the bore via a mirror and then from there once locked down I then attach a scope mounted bubble level and then level it via a plumber line.

[Mackado]

coincidently I just went through adjusting Cant for the first time, turns out I was also way off doing it by 'eye'  and my New Bugbuster scope was losing Zero because elevation setting was maxed out, did some reasearch and turns out you are not supposed to go beyond 3/4 on the adjustment range or Zero is lost.

I was able to slide a small level on the bridge (open cover) of my vintage crosman 140 pumper, the only flat part available, once the gun was leveled I used a second circular level used on TurnTables platters (record players) I had handy, and placed that one on top the Picatinny adapter attached to the barrel, luckily, turns out the level's edge fitted between the grooves, made sure both levels were aligned before tightening the picatinny in place and went ahead and mounted the rings and scope (also shimmed the rear of scope), moved the circular level over the flat elevation turret knob and aligned the reticle by moving the tube, to my surprise the Bugbuster now was almost at Zero (10 yards) and needed very little adjustment, I figured out the turrets 'mid-point' range by counting turns and both elevation and windage are now just inside the 1/4 adjustment range.

I'm sure it's not perfect, I need to find better levels suited for the job and a proper Rifle rest, but I'm happy with my results, and after many rounds testing, the Bugbuster still holding Zero.

[bandg]

Installing and using a level correctly is certainly helpful for precision shooting.  For those instances when you may have a quick shot and/or no level available, one can scan the background quickly and use the tree trunks for a vertical.  It's never perfect but it will get you close enough for a reliable shot in most situations.  Terrain can throw perception off but the trunks of trees are usually relatively vertical.

[shooter r]

The tilted background makes for some optical illusion on the second picture. It could be aligned OK, compared to the flag pole. (The first picture doesn't come up).

Here is one way to "test by fire" if your scope is mounted correctly, and you want to use a "hold over" technique for distance.

In this test you must be sure you are holding your rifle square to the ground, that is the toe of the stock, barrel and top of the scope are in a line perpendicular to the ground. A spirit level is helpful.

With a TALL target that has vertical and horizontal lines on it, be sure the horizontal lines are "level". For a pellet gun, place it about 15 yards away.

Put an aiming dot near the bottom of the target on one of the vertical lines. (This will work best with guns that can shoot 3 shots in the same hole at 15 yards!).

Shoot a group at the aiming dot using the center crosshair of the scope. THEN... (keeping your gun level!) use the bottom part of the vertical crosshair ( the "+" will be quite high on the target) shoot another 3 shot group. The second group should be directly above the first group, if it is not, you should consider readjusting your scopes rotation in the rings if you plan on using the hold over technique.

[mcoulter]

Oops!  I did not realize the 1st photo was not coming up for people.  I have fixed that!

[mcoulter]

Here's a quick "box test" where I tried keeping my rifle's crosshairs visually vertical vs. allowing the rotation that really gets me vertical.  I made a very nice parallelogram instead of a box!

I shot at the bottom left dot and then keeping the POA the same I went 20 clicks right, 20 clicks up, 20 clicks left, and then 20 clicks down.

Don't trust your eyes!




Target was a 35 yards with a UTG scope at 16x.  I got more movement from these 20 clicks in elevation than in windage.  But my last shot DID return to the same POI as the first shot.      The horizontal change was 2 mildots for these 20 clicks (roughly 1.5 inches)   Oh, and these were shot with my D34 .177 vs. the Royale that I used in my original post...

 

[Fussell]

I use a bubble level on all my rifles and pups. I mount the bubble level first. Then set a plumb line out anywhere from 10 yds to 30 yds  to align the crosshairs before tightening the scope into the rings. I'm shooting from a rested position mostly anyway, be it off bipod from a bench or table at home to a trigger stick in the field. Darn Thomas weighs over 12 pounds scoped, not really an off hand kind of gun.

I put a couple of small neodymium magnets on the back two hex head screws that hold my aluminum cocking lever plate down. Put a small magnetized bubble level there for easy removal. Maybe I don't have the cant 100% knocked out, but at least I have the rifle back to the same position every time by eyeballing the bubble before I squeeze.

[Scotchmo]

I use a bubble level on all my rifles and pups. I mount the bubble level first. Then set a plumb line out anywhere from 10 yds to 30 yds  to align the crosshairs before tightening the scope into the rings. I'm shooting from a rested position mostly anyway, be it off bipod from a bench or table at home to a trigger stick in the field. Darn Thomas weighs over 12 pounds scoped, not really an off hand kind of gun.

I put a couple of small neodymium magnets on the back two hex head screws that hold my aluminum cocking lever plate down. Put a small magnetized bubble level there for easy removal. Maybe I don't have the cant 100% knocked out, but at least I have the rifle back to the same position every time by eyeballing the bubble before I squeeze.

That receiver mounted level can only indicate when the top of the receiver is level. It does not really indicate cant.

When mounting a scope and anti-cant bubble, the scope should to be tightened in the rings BEFORE you align the reticle with the plumb line. Then you adjust (rotate) the bubble level and tighten it to indicate that the gun/scope is vertical (eliminating gun cant).

[Fussell]

Dangit Scott, I always do things bass akwards! LOL
Well, it's been working for me? Thanks for the correction man!

50 yds with the Thomas. Now if I could just rid of the flyers ;-)

13.4 gr Monsters at 818 fps scope zeroed at 28 yds