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Rotation or Cant problem?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/28/2008 at 22:15
sakomato View Drop Down
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I have a Kahles 4x12x52 MultiZero on a 300 win mag.  For those unfamiliar with this scope it has a top turret where you can set a stop at a 100 yard zero and set the next marks to correspond to whatever distance you want
 
 
I ran the ballistics on my load and set some POI's for presetting the marks at the 100 yard range.  The target looks like this
 
 
This shows 2 shots at the 200 yard dot, 1 shot at the 300 yard dot and 1 shot at the 500 yard mark (I had already set the 400 yard mark).  Notice how the POI shifts to the right with the additional clicks on the elevation turret.
 
Now to my question, is this a problem with rotation.  I made a sketch to show what I'm thinking
 
 
If you are adjusting the elevation turret and the scope is rotated the reticle would be moving along axis A which would force you to raise the crosshairs to point G and then over to the crosshairs which would move the POI to the right along axis D.
 
Am I all wet on this or would rotating the scope counterclockwise a little correct the problem.  Or is this a problem with Cant which is just not holding the rifle in a position so that the center of the scope is not directly above the center of the bore?


Edited by sakomato - August/31/2008 at 22:20
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 03:27
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Well, it certainly appears to be a rotation or cant problem. You will only know which one by eliminating the rotation as a possible reason. This can only be done by using a plumb line and finding a way to set your rifle dead horizontal. So you would set your rifle dead horizontal and then look at the plumb line, as far as possible away from you, and see if your vertical line matches the plumb line.
Or there may be som fancy cadgets that check this.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 04:28
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Yes, there are some little laser beam-y things that you can attach to a laser bore sighter which project a horizontal bar of "laser light" on whatever surface you're pointing your rifle at, and once your rifle is all locked down and straight, you can coincide your crosshairs with the perfectly level "beam of light".  I've seen them in catalogs.     --Ed
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 04:47
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I have re-looked at your post and re-called an article I read on the effect of cant on POI. Cant effects the POI less then rotation would, because gravitational pull somewhat corrects the path of flight.
So to me it seems to be rotation. But I speculate. You need to check if your scope is in correct alighnment using a proper method of measuring.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 05:34
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I find this thread quite interesting, but if you would exuse my ignorance in the area of physics, are we talking about the rotation of the earth or the rotation of the bullet itself?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 05:40
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No we are talkink about the rotation of the scope in relation to the axis of the bore. In other words has the scope been mounted horizontally and vertically in line with the axis of the bore.
A rifle will shoot a string to the left or right if the vertical line of the scope is canted and you make adjustments up or down. The cant can be because the scope has been mounted at an angle (rotation incorrect) or because the shooter is holding the rifle canted.


Edited by 8shots - February/29/2008 at 05:41
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 08:30
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I have a Zeiss Conquest that I mounted on a 7MM. After sighting it in I noticed that it was doing the same thing. I thought it was mostly me, shooter error, but after remounting, releveling and making sure that I did the best I could to make sure everything was correct. A solid rest is needed, I leveled the gun, leveled the scope and made sure that it was as true to vertical as I could possible get it......all better now. 
PS......How do you like the scope? I have been thinking about a Kahles, don't know about the Multi-zero though.....

Edited by medic52 - February/29/2008 at 08:32
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 09:15
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Even the slightest wind could move your bullet that much at those distances.  A 2mph wind could move a 190 gr .30 cal bullet 3.5 inches at 500 yards.  So don't rule that out either. 
All you need to do it set a level on the base of your gun and make sure it is level, then put the scope into the rings and make sure it is straight and stays straight as you tighten stuff up.  No fancy tools are needed.
Spin drift is not going to start happening until you get down range quite a bit further.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 11:13
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I take it you shot all those target at 100 yards to simulate target ranges from 100 to 500 yards. If so, that pretty much eliminates the wind drift. I would lean, no pun intended, to the rotation or cant problem. Level the gun, then level the scope and re-shoot it. If its good, then you solved it. If you still see the same thing, let someone else shoot it. Maybe you are canting the rifle. Let us know how this turns out. I am seriously looking at purchasing this same scope for my .300.
Ryan
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/29/2008 at 19:30
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Thanks for all the responses.  It's nice to post somewhere where someone understands and even wants to talk about things like this. 

I have been thinking further on this and some things come to mind
  1. Rotational error would have no effect on scopes that do not have ballistic reticles or where the shooter does not count clicks up for elevation.  If the shooter just raises the crosshairs an estimated amount to allow for bullet drop, rotational error would not matter.
  2. Rotational error would matter in rifles with ballistic reticles like the RapidZ, TDS, etc. for the same reasons it matters on the MultiZero.
  3. If you had one of these  
    mounted on your scope and you clicked 30 up, if the POI was straight up then your scope would be uncanted and rotationally correct  (I ordered a couple)
  4. If you didn't have a scope leveler then cant could create as much or more problem than rotation

rkingston, I have 2 of these scopes, one with a 4a and one with a plex.  I prefer the 4a.  They are excellent scopes.  I was a little worried about making minor changes in the 100 yard zero and the subsequent resetting of all the marks.  Thing is, and I don't know how, when you reset the 100 yard zero a few clicks and rotate the turret to reset the stop, it brings all the rest of the marks to the new setting so you still have the same number of clicks between the yardages, no resetting necessary.

There are a couple of real advantages to this type of scope.  One is that this scope will work for whatever gun and whatever load you use.  IOW, it's not like a TDS or Ballistic Plex where you have to shoot a load that approximates the reticle trajectory, you set it yourself.
 
Another is that you can set the scope very close to any yardage you are shooting at.  For instance 330 yards

or 450 yards

 
One thing I am sure of since I started shooting at the longer ranges - I will not buy another scope without some method of setting holdover, either this MultiZero kind or a ballistic reticle.  So far I have a TDS reticle, 2 MultiZero's, 1 RapidZ 800 reticle and one Ballistic Mil Dot reticle.  It is a lot more exact then guessing how far a 19" holdover is at 400 yards.


Edited by sakomato - August/31/2008 at 22:22
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 04:48
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MAN what a GOOD DOG you have..........I love well trained hounds.....I don't know about the rings, looks like you could spend to much time worrying about that bubble. I think if you do your mounting correctly to start with you eliminate the potential problem...but I am curious to see how you like them.......

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 09:30
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 While on this topic, here's a somewhat related issue:  Has anyone here ever wished that scope manufacturers would etch a thin line lengthwise along the Bottom Dead Center of the tube, to match a corresponding hash- mark on the Bottom Dead Center of the lower ring saddle to facilitate perfect mounting the first time you tighten the screws?
 (That's the amatuer machinist in me thinking out loud, anyway...)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 09:57
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8shots has it right.  Usually I do not do it, but making sure the reticle is centered from the factory is a good thing to do and not difficult.  Just place in a ring set or v notches in a cardboard box and rotate and make sure the cross hairs x do not move.  When mounting the scope, I use a simple 4 inch low profile level on a flat surface of the action, held in place by a rubber band.  I double check the level by going over the rifle in other areas with another level.  Some times the rifles are not bedded into the stock level and can be canted in the stock.  I this is the case, then you have to decide whether to mount the scope level with the stock or the receiver.  It depends on how you shoot.  If you are shooting based on how the stock feels than the latter would be preferable.  I tend to always keep my vertical cross hairs always up and down and level to the receiver.  After doing that, I set up a plumb line at a distance that is easily in focus for all magnifications of the scope and line up the vertical with the plumb line at the lowest magnification and tighten things up so the scope will not move and then go up on the power and make sure nothing changes.  If anything changes, it will be to the left or right, as you will find it hard to note any change up or down, which would be more common, unless you mark your plumb line.  This is the easiest way to prevent any cant or rotation of the scope in the mounts with reference to the receiver and is easy to do without a lot of expensive equipment.  One caveat.  Some rifle receivers do not have a flat portion to use and others, the flat portion is difficult to access.  Also, some are not perfectly flat.  Overall this works very nicely.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 11:19
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Well, I rotated the scope just a very little counterclockwise
 

and took it shooting.  It seemed to work.  The reason I say "seemed" to work is because I don't trust anything until it repeats itself 3 or 4 times.  The POI was directly above, but the question is - was the rifle canted or not?  The reticle appears to be a little rotated when I shoulder the rifle.  It may be that I have been canting my rifle all these years.
 
The reason I want the bubble is that if in fact I am canting then maybe I can learn to uncant my rifle.
 
The plumb line is a good idea and one I have heard before.  I have not tried it since I haven't had a plumb bob since I hung my toolbelt up about 30 years ago.  But there again, there is no way to tell if the bore of the rifle is hitting dead center on the plumb line while the scope reticle is.
 
 
As far as centering the reticle, has anyone heard of the mirror trick, where you put a mirror in front of the objective and look throught the scope and adjust the shadow reticle to coincide with the real one?  The trick is getting enough light onto the mirror surface to be able to see, and not occluding the sight picture altogether.  I have not tried it but have heard it works.  I usually take a new scope and count clicks from one side to the other and go back halfway.
 
Anyway, it would be interesting to see and certainly a good test for anyone to count up 30 clicks, shoot one shot and see what happens.
 


Edited by sakomato - August/31/2008 at 22:24
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 11:26
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I guess this site does not permit putting in a link to a competitor.  When I am typing the post, the link shows a link to M----y, but it posts something else.  Let me try again
 
 


Edited by pyro6999 - March/01/2008 at 11:30
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 11:26
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I give up
 
Loco
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 11:28
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There really is no reason to buy the system above.  For less the 5 bucks from Lowes you can be set up to get a perfectly aligned reticle everytime.  In fact I am getting ready to mount a scope just shortly.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 16:01
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sakomato, how are you liking the Rapid-Z 800? have you been able to check the elevation marks at all ranges yet?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 16:49
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Originally posted by trigger29 trigger29 wrote:

sakomato, how are you liking the Rapid-Z 800? have you been able to check the elevation marks at all ranges yet?
 
No, the rebarrel is fairly new and I am still working up loads for it.  That problem was compounded by the fact that there is very little data out there for a 6.5 rem mag and I had to start way low and see what the gun likes.  I think I am about ready to declare that it likes the 140 gr bullets better than the 130 Accubonds.  It seems to like RL25 with the 140 gr bullets at about 3000 fps and I am set now to try different bullets.  Almost there but I have not shot it at the longer ranges.
 
Like all Conquests the clarity is amazing.  The reticle is very well done, thin but jet black and crisp.  The reticle not going all the way to the edges is not noticeable when shooting.
 
One thing about the RapidZ Calculator on the Zeiss site is that it will only calculate for a 200 yard zero which I suppose is best since the ranging bars are labeled "3, 4, 5, 6, 7 and 8".
 
The 44 mm objective has an attractive low profile
 
I like it.


Edited by sakomato - August/31/2008 at 22:25
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 16:58
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/01/2008 at 18:22
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Just trying to fit in!  Big%20Grin
 
The only problem I've encountered so far with this is that the scope is at the bottom of the elevation adjustments.  If I had to adjust the scope so the bullet POI would be any lower, I would have to shim under the scope at the front rings.  Probably because of the Weaver type bases for the older Browning BBR not being exactly right.
 
Luckily the 140 grain bullets have a lower POI than the 130's so I am going in the right direction.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/03/2008 at 01:29
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Sakomato, the mirror trick is not to center your crosshairs. To center your crosshairs you can count the clicks, or you can rotate the scope like suggested somewhere earlier on the post. As you rotate the scope the cross should not move.
What the mirror trick shows you is whether the scope has been mounted in alignment to the axis of the bore. This can only be corrected if your scope mounts have windage adjustments. In other words is the the center of the ocule and the center of the objective lens in proper alignment with the axix of the bore.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/21/2008 at 20:27
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Hey 8shots
 
 
Hope the link comes through, but anyway you hold the mirror against the objective and look through the ocular.
 
Trouble is I don't have a portable mirror or I would try it.  Sad
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/21/2008 at 21:23
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Originally posted by sakomato sakomato wrote:

Thanks for all the responses.  It's nice to post somewhere where someone understands and even wants to talk about things like this.

I must say I'm a bit disappointed to see this.  When you posted the problem on another board I asked you two very simple questions but very important ones in an effort to help diagnose this problem. 
Quote First, did you set up the target with a level to make sure it was straight? Second, when you shot at the target, did the vertical crosshair go through all the dots ensuring it was square with the target?

You never answered.  Had you, you wouldn't still be asking this question:
Originally posted by sakomato sakomato wrote:

the question is - was the rifle canted or not?  The reticle appears to be a little rotated when I shoulder the rifle.  


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/21/2008 at 23:00
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Must have missed that question but the answer is no, the target was not posted with a level.  It was however level to the eye when using the ground, the boards and the other targets.  I do not see how the target could have been off perpendicular enough to cause the 3" or so track to the right.  There is a possiblility that the dots could have been off vertical by 1/4" or so in the 10" of rise but anything more would have been evident.
 
Yes the vertical crosshairs did go through all the dots.
 
So now that I have answered the questions in such a way as to make the questions irrelevant to the answer, is it permissable for me to continue the conversation?
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