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cant revisited |
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jackG
Optics Apprentice Joined: November/27/2006 Location: United States Status: Offline Points: 141 |
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Posted: May/02/2008 at 07:33 |
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I skimmed through the posts on the subject of reticle cant (or tilt) and didn't see the following question addressed. If might have been but I didn't catch it.
I spoke with my brother last night describing my new scope installation. I repeatedly threw the rifle up to my shoulder, resting my elbow on a table in the kitchen, to determine the correct eye relief and to square the reticle. Once I got the reticle square to the horizon, at least visually, I noticed the rifle is slighlty canted to the scope. It's not off by much, perhaps a couple of degrees or so.
My brother recommended that the rifle being canted would screw up efforts to make adjustements when sighting in. I can see if the scope is canted that inputs to elevation would effect windage, I think. But would the rifle being canted have some similar effect? That seems counter intuitive to me. On the face of it, it seems as if the rifle canted or not, zeroed to a level scope will produce a hit at the point of aim. The canting of the rifle this way or that shouldn't matter provided you do the same way each time, as evidenced by the reticle being level. He argued that the rifle must be leveled, then he scope trued to the rifle and the horizon to have it shoot accurately. Is that correct?
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Rancid Coolaid
MODERATOR Joined: January/19/2005 Location: United States Status: Offline Points: 9318 |
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It depends.
If you can shoulder the rifle in EXACTLY the same way each time, and if you always shoot at EXACTLY the same distance, there will be no change due to cant. If, however, you EVER shoulder the rifle differently or if you EVER shoot a different distance or make any manner of reticule adjustment with the windage and elevation turrets, you will have issues. In short, a line passing through the center of the scope (along the vertical post) should continue down through the center of the bore - the horizontal line, for cant purposes, is irrrelevant since that is the line that will move according to range. If the vertical isn't vertical or if it is vertical but on a line other than the center of the bore, any adjustment to the scope, either in vertical or horizontal adjustment, will be off. Almost everyone cants their rifle when they shoot off-hand. If the distance shot is not long, cant won't matter much hunting. Finally, in my opinion, NEVER level your scope by eye on an off-hand hold. Allowing a shooting deficiency to be so well established is a very bad thing for precision shooting. Offhand, I cant my rifle by about 3 degrees. My scopes are mounted exactly level so that when I should the rifle, it looks off and I rotate about 3 degrees to be where I should. If I mount a scope with an off-hand hold, it will always be about 3 degrees clockwise - and when I dial from a 100 zero to a 600 shot, my rounds are all low and right of my target - which severely pisses me off. Mount it right and be done. It will take a few extra minutes and some effort, but nothing sucks more than missing a trophy because you decided to save a few minutes on mounting your optics. Edited by Rancid Coolaid - May/02/2008 at 08:26 |
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trigger29
Optics Master Extraordinaire X = 180 Y = 90 (X+Pyro)+(Y-Pyro) = ? Joined: September/29/2007 Location: South Dakota Status: Offline Points: 4353 |
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+1 on that. I spent extra time and care on mounting for my long range rifle, and it has paid off very well. The long shots are much easier when everything on the rifle is true.
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mercenary1947
Optics Master ** Joined: April/02/2006 Location: United States Status: Offline Points: 1392 |
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I agree ... I would rather teach myself to aim level than miss shots . By that I mean practice keeping the crosshairs/rectile straight when firing as it was setup . 8shots did a long and technical test at his own expense to show what different canting of the scope and/or rifle made on hitting the bulls eye . If I can find it ... I'll post a link or you can look him up for the posted link . Very informative !
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8shots
Optics Jedi Knight Lord Of The Flies Joined: March/14/2007 Location: South Africa Status: Offline Points: 6253 |
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JackG,
If you raise your rifle to your shoulder, without looking if it is canted or not, but your scope is level, as described by yourself, the adjustments would be true. In other words if you dialed up, the elevation would go up only. The impact of the bullet would also go up only. This will only be true at short distances. As soon as you move out to distance of probably in excess of 200 yds, the arc of the bullet will be effected by gravity and will move left or right and downwards. At this stage it is gravity doing its dirty work, not scope cant or rifle cant. However, a rifle zeroed with canted scope or rifle or both, is just that. It is zeroed and will hit the point it has been zeroed to. Edited by 8shots - May/02/2008 at 10:01 |
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mercenary1947
Optics Master ** Joined: April/02/2006 Location: United States Status: Offline Points: 1392 |
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That was quick ..... you did'nt mind me sending him to you did ya 8shots ? I figured if anyone knew you did after reading your test post .
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8shots
Optics Jedi Knight Lord Of The Flies Joined: March/14/2007 Location: South Africa Status: Offline Points: 6253 |
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Mercenary, if I just see the word "cant" I go all shaky and weak kneed. I thought when I saw the thread, "Oh no, not again....."
My head is all canted and full of canting stuff!!!!
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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You guys at it again!!
I think this post will address the problem (or lack thereof) that you are worried about
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The effect of a canted scope verses a canted rifle...
This picture represents a canted rifle underneath a level scope. You're looking at the buttstock of the rifle, and on through the scope. The orange circle is the approximate location of the bore of the rifle. The blue dots represent the fall of the shots as they go downrange; they fall with gravity along a line which is represented by the vertical crosshair in the scope. What we must concern ourselves with to understand this issue is the scope and the bullet path. When you dial the scope's erector to zero for windage, you are essentially aligning it with the bullet path--not the barrel! So if a scope is mounted slightly canted, but held level, the bore of the canted rifle would only be off to the side a fraction of an inch (perhaps 1/16 to 1/8 inch) underneath. It would look something like this: Is it important that the bore isn't 100 percent underneath the scope's vertical crosshair? Actually, no. Think about it this way: If you have the scope dialed to a perfect 100 yard zero with one particular load, and then you switch to another load, you'll likely note that your windage zero will change. Has the scope moved? No. Has the barrel changed? No. Only the direction that the barrel is throwing the shots has changed. Barrels, by their very nature, throw shots here, there, and yonder. So you must dial the scope's erector to follow the general path of the new load to get your zero. This may take the scope's centerline well away from the boreline--but that's not what's important. Bullet path and boreline are two different things. You see, the scope's erector is never actually aligned with the bore of the rifle to begin with--it is aligned with the path of whatever bullets you are setting the zero for. What I'm saying is that you can have a slightly canted scope, with the barrel underneath at, say, 5:30 and so long as the scope is held level, the shots will still fall parallel with the vertical crosshair. In the top image, there is the ideal situation where the scope's vertical crosshair perfectly disects the fall of the shots. In the second image, the scope is mounted with a slight cant, but since the scope is being held level, this means that the rifle bore is off by a bit underneath it. It's at 5:30 rather than 6 o'clock. Note how the shots fall just slightly to the right of the vertical crosshair. Groups forming downrange would probably never indicate that the 5:30 rifle cant even existed, as these shots would only be off to the right of the vertical crosshair a tiny fraction of an inch. What if you layed the rifle on its side? If you layed the rifle on its side (and mounted the scope upright, with the elevation turret up top), ...this would of course put the scope about 1.5 inches to the left of the bore. If you zeroed the scope for the shots to fall dead on at 100 yards then yes, you would have an angular relationship with bullet path and line of sight. You'd only be zeroed for 100 yards. From the rifle to the target, you'd begin with almost 1.5 inches of error, slowly correcting until you got to 100 yards, then beyond 100 yards your shots would deviate farther and farther from the windage zero you had at 100 yards. However, if, as is shown in the drawing immediately above, you were to take into account that 1.5 inch difference with the "sideways rifle," and you dialed the scope so that the shots fell 1.5 inches to the right of the crosshair intersection at 100 yards, these shots would stay only 1.5 inches right of the line of sight all the way downrange (wind factors and such notwithstanding). In another possible scenario, you could simply take this sideways rifle and dial the windage zero to be correct at 1000 yards. Then, you'd be off a little less than 1.5 inches at 100 yards, and the bullet would begin "closing in" on the windage--and the closer the bullet got to 1000 yards, the more it would close the 1.5 inch gap. At 1000 yards, the bullet would cross the line of sight, then begin deviating in the opposite direction, and by 2000 yards, it would be about 1.5 inches to the other side. Obviously, this 1.5 inches would not be much of a factor at the longer ranges. So, with the slightly cant-mounted (but held level) scope, you're not going to be off anywhere near 1.5 inches all the way downrange. It'll be more like 1/8" or so--and wouldn't even be noticed in a 1 MOA group size. So remember: It's bullet path, bullet path, bullet path--not the barrel that you're aligning the scope with. The above is a top view, looking down at the rifle and scope, and bullet path(s). The blue area would represent the scope's range of WINDAGE alignment; in other words it can be dialed to windage zero anywhere in that blue zone. The orange lines represent the various paths different load recipes might cause the bullets to fly. You can dial the scope to align with any of these paths. All that really matters is that the bullets be released relatively close to the vertical crosshair and all will be well. When the barrel releases the bullet, the bullet goes up, then it comes down. It does this regardless of where the barrel is in relation to the scope. All you are doing with the scope windage adjustments is aligning the erector to be closely parallel with that bullet's path. The key words here are CLOSELY PARALLEL, and once the scope's windage is set to be parallel with the bullet's path, you will not have to change windage for various ranges--it'll stay the same--even if the barrel is at 5:30 or 6:30, or even 5 o'clock or 7 o'clock underneath the scope. You might get lucky and have your bullet fall perfectly along the vertical crosshair of your scope, but that'll be the exception; not the rule. Chances are, if you could somehow determine the "perfect bullet" path, it would be 1/8" or even more, to one side or the other of the vertical crosshair. Big deal, though--such a small amoun |
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jackG
Optics Apprentice Joined: November/27/2006 Location: United States Status: Offline Points: 141 |
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A very good explanation. I was poking at this quesiton all afternoon and talked to several co-workers. Some felt that it made no difference. Zero is zero regardless of what the rifle is doing. Others wouldn't buy it. In end I could envision a canted rifle, being perfectly zeroed at 100 yard, but that in fact that was not two paralell lines, one from the bore and the other from the scope. It was actually a point of intersection between the axis of the scope and the axis of the bullet's path from the bore As he bullet passed through that point it would travel slightly away from the scope's axis.
I think we talked ourselves into thinking the amount of that deflection could be represented by the scope height above the rifle say, 1.5", and the degrees of cant subtracted from 90 degrees. Say three degrees of cant subtracted from 90 would be 87 degrees. Take the cosine of that and multiply that times the distance the scope is above the bore. It's not much. But out at say 200 and then 300 yards it becomes more significant. That error would increase linearly with distance.
The cure is as everyone has recommended. Level the scope to the rifle the scope to true horizontal, or vertical, depending on your reference. I confess when I installed my first scope, I eyeballed it. And apparently it got it close enough, as it shoots to zero windage out beyond 300 yards. I bumbled my way to success. I'll use the proper tools this time.
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mercenary1947
Optics Master ** Joined: April/02/2006 Location: United States Status: Offline Points: 1392 |
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I use the laserlyte system .... have you seen those ? Some only work with steel because they rely on magnets .... those don't . Or sitting a lil level on system that can slide off . Like everyone .... for years never heard of levels and bubbles .... lasers make the whole nine yards of setting up perfect . I sight my rifles in at 150 yds. ... then and rely on mil-dots for under and over .
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Well, I would caution that when one talks of 3 degrees that is less than 1/2 of one minute on the clock face (90 degrees is 15 minutes, 180 degrees is 30 minutes and 360 degrees is 60 minutes). That amount of cant is unnoticeable.
From my experiments with the anti-cant bubbles I have recently installed on my a couple of my scopes I will say that if I set up to shoot, the bubble is almost always not in the center, usually not far off, but not in the center. I shoot off an adjustable front rest with a notched leather sewn bag and a rear leather sewn notched bag and have been doing so for years.
Holding your rifle to the exact same cant or position every time to within 3 degrees everytime without a lock in rest or an anti cant device would have to be demonstrated to me. I would estimate that normal variation in rifle position for most of us experienced and good shooters is closer to 10 degrees (less than 3 minutes on the clock face) to either side of straight up with most of it falling at 1/2 that or less. I don't know, I'm just guessing.
Now I go Elk hunting and most times the herds are spotted in the dark timbered slopes from across the canyon. Shots have been from 200 to 400 yards and there is plenty of time for set up. My last shot was at 253 yards slightly down taken with a 300 win mag and 180 TSX. I hit about 3" to the left of where I expected. I attibuted that to wind which I had allowed for, but was it? Next time I will know and if the shot is 400 or 500 yards rifle cant and scope cant will not be a part of the problem.
mercenary, I have a bore sighter with which you look through the scope and adjust the reticles to the grid. I also have use a laser light system that has the cases with the laser in it. Those devices will do nothing to correct scope rotation and align the vertical reticle with the bore. They are useful for zeroing the crosshairs only. The scope could still be rotated in the rings and the rifle held at a cant and the boresighters will not be of use to correct the problem. Back in one of the previous threads you will see that someone suggested I use a boresighter and crank elevation and watch to see if the crosshairs moved parallel with the grid. It did so I rotated the scope and tried it again. You automatically can rotate the bore sighter to accomodate the scope rotation so the crosshairs will again move parallel to the grid on the bore scope.
Like the article said, by far the most important thing is holding your reticle level and perpendicular.
Although here's some more to think about and 8shots to get weak-kneed over
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