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Rotation or Cant problem? |
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Just trying to fit in!
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.
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Guns only have 2 enemies, rust and politicians
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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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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.
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Hey 8shots
I knew I saw this mirror trick somewhere http://practicalrifler.6.forumer.com/viewtopic.php?t=28&highlight=mirror
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.
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Guns only have 2 enemies, rust and politicians
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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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.
You never answered. Had you, you wouldn't still be asking this question:
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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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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Guns only have 2 enemies, rust and politicians
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mercenary1947
Optics Master ** Joined: April/02/2006 Location: United States Status: Offline Points: 1392 |
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What scope " mounts " are you using ? Had one fellow buy a pair of mounts that were just not keeping the scope where it should stay when he tightened them down . It's not mentioned on here much but a good set of mounts/rings are a must ! And I've even seen some about crush the guts out of a scope warping the tube .... I do use a a laser setup now ... would'nt sight in without one . Never saw a setup that far off = impact that far to the right .... with everything correctly mounted ... hard to diagnose without the setup in my hands ... and I won't even try . Of course a few pull the rifle on squeeze everytime not realizing it .... had a couple over the years had impact all over the place and it was them flinching when pulling off a round .... they tried to blame the scope ... but nope ! Had to show them .
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One Shot One Kill .... *S.O.F * Head Shots Only
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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I'm using Talley's, http://www.talleyrings.com/fixed.php the fixed ring kind not the quick detachable. I have used Talley's, Warne Weaver style, Sako Optilocks, Leupold Dual Dovetail and Redfield style with the rear windage screws. Talleys are the hardest to get put on but once there are like a rock so that was not the problem.
I did rotate the scope in the mounts and it has solved the problem through 2 shooting sessions now. However, now I am on a fact finding mission to figure out an unfallable way to mount scopes with the verticle reticle perfectly aligned with the bore as the bore is progressively raised during long range shooting. I suspect this will also have an element of eliminating rifle cant along with precise scope mounting. I'm working on it
I only resurrected this thread to note the mirror thing and see if anyone had tried it.
Hey Dolphin, what is your method? Edited by sakomato - August/31/2008 at 22:27 |
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Guns only have 2 enemies, rust and politicians
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ccoker
Optics Master Joined: February/13/2008 Location: Austin, TX Status: Offline Points: 2041 |
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interesting, I just got two 3-10x50s, one with a plex and one with a 4a reticle, I prefer the latter but got the Plex for a smoking deal so, I will use it
the 4a will go on my new Sako 85 Finlight 270 which will be my main hunting rifle, the standard plex on my Tikka stainless lite 308 hopefully tomorrow I can get to the outdoor range to start setting up for 2 and 300 yards then in a few weeks to get to a friend's place to setup 400 yards I REALLY like these scopes my 4.5-14 conquest is now on my new Savage Varmint 204 |
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Dolphin
Optics Master Joined: October/05/2006 Location: North Carolina Status: Offline Points: 1795 |
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Nice rifles Sako. I just purchased for a couple bucks a 4 inch low profile level and some bright, sort of purple colored plumb bob string, any color would work, I just liked it. Using a rubber band, I attach to the hooks on each end of the level, I place the level on a flat surface on the receiver of the rifle. Of course I place the level first then attach the rubber band to secure it in place. The only problem with this, is that some rifles do not have a flat surface. You can use the mounts after attached, but then you assume that they are in alignment perfectly with your rifle and you have to keep your rifle locked down while mounting the scope. At any rate, after getting the scope into position, with the rifle level and adjusting it to your eye relief, just rotate the reticles until the up and down cross hair perfectly over laps with the plum bob line hung from what ever way you choose. I hang mine from a tripod from the side of my truck. Some people skip this step and choose a door frame if the door if level after checking or if the door does not move on its own. I work in a garage and have to use the plumb bob line and like the pure accuracy of knowing it is right. I have a one scope, a Burris FFII that the reticles were way off from alignment with the turrets, not some much that I wanted to send it back, but every time I look at it in the mounts, it is sort of irritating, since I am some what of a perfectionist about those things. Its the only scope that has been that way, from the cheapos to the most expensive I own.
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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I'm not sure how it makes them irrelevant. When trying to find the cause of a problem, eliminating variables/possible causes in a systematic way is a good approach and you haven't done any of that. The cause could be one of any number of things or a combination of many--you don't know. To the reason I asked: I agree it would be difficult to have posted the target crooked enough to cause the error. Then again, if the target frames are crooked, or if it's on a hill, etc, there are many ways your eye can be fooled enough to cause an error. It also may have only been a small contributing factor. Setting them up next time with a level and you'll know they're straight. I also think it would be difficult to cause that much error by canting the rifle if the targets were straight. Since the scope was straight with the targets, it would need to be seriously offset from the boreline to cause such error. It too, may have only been a contributing factor without being responsible for the entire error. All that plus the fact it's tracking straight for you now but the reticle looks canted to you now just reinforces the possibility of another cause--a mechanical problem with the scope, a reticle canted with respect to the turrets. If this is the problem you're going to continue having problems and chasing your tail. If the reticle looks canted to you, you will naturally put it "straight with the world" before you pull the trigger from time to time. If that causes a miss your equipment is not acceptable for this use IMHO. If this is responsible for the entire error, it would have to be canted a lot--well out of their specs so they would fix it for you. You need to determine if this is the problem first. Luckily, this is easy to do so you can either discover it is a problem or eliminate it as a possibility. This is the very first thing I do with a scope I'm going to crank elevation for distance with. My prefered method is using a boresighter. No, they're not just for boresighting: You line the reticle up with the grid and start cranking away. For this scope, you can see it stays withing ~1/2 MOA over the span of ~70 MOA. That's quite good. It could move laterally 3.5 MOA and still pass within Leupold's spec of 3 degrees (which I feel is unacceptable). If your scope has this error and you don't discover it, you're just shooting yourself in the foot for future as it's always going to cause you problems. You don't need a boresighter to do this either. You can do it by lining the reticle up with any straight line and cranking the elevation. The line needs to be straight, far enough away you don't have parallax error and you need to hold the scope/rifle steady. A vice is good, but sandbags can work especially if you have a buddy to crank the knob while you hold the rifle steady. I suggest measuring over the largest number of clicks practical for accuracy and you can repeat as many times as you need in order to be sure of the results. This takes wind/shooter error of any type out of the equation. It can be mounted on the rifle sideways and it will still work. Now, if you want to be really productive, it's a good time to measure your click value while you're at it. They don't always agree with what's printed on the knob. If yours are off, now's the time to find out. This only means you need to have measured values along the line. Here's one way I like to do it: (I apologize for the poor picture quality.) Here you can also see the target frame is not square with the target or yardstick. Which is correct? And of course you can check the calibration of any reticle features you may be wanting to use at the same time.... In short, even good manufacturers make mistakes. If you want to avoid frustration and wasted ammo at long range, check your equipment. By doing the above you'll either discover a canted reticle is contributing to your problem and can send the scope back to be fixed, or you will eliminate it and can cross it off the list so you can focus on the other posibilities. |
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Hey Jon
Excellent post and contrary to your opinion, excellent pics!
I do have a boresighter and I will set it up in a minute to try this out. So you are saying that if the vertical reticle is set up to be visually in line with the vertical of the boresighter, then clicking up should show the vertical reticle staying in line with the boresighter.
Back in a minute, just wanted to say I appreciate your post.
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Guns only have 2 enemies, rust and politicians
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Okay, the scope only goes 58 clicks which is one full revolution and then it hits the back of the 100 yard zero stopping point. I could put the scope in Mode A and it would continue cranking but I really don't want to mess with the zero right now.
Anyway the vertical reticle stayed perfectly in line with the vertical line on the bore sighter. I do not know if it would have before I rotated the scope so I may have solved the problem before I had a chance to apply this method. If the scope was rotated would the reticle and bore sighter have stayed in line while cranking elevation? The bore sighter can be rotated in the muzzle also.
I just answered my own question, I artificially rotated the scope in the mounts by a noticeable amount and then rotated the bore sighter. The vertical reticle stayed right on the bore sighter vertical while cranking elevation. So I don't think that a bore sighter can be used to level the reticle.
Back to the drawing board. Right now I'm thinking that using the anti-cant bubble and cranking the elevation up and see if the POI's are vertically in line might be a viable method of aligning bore and scope.
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Guns only have 2 enemies, rust and politicians
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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Excellent. Now you know your scope is good so you can completely cross that off the list and focus on the other things.
Crooked target, canted rifle or some combination of the two are the big ones left. Try and be meticulous about setting up the target next time to eliminate that. Sighting down the target shown, it seems the top couple of dots are out of line slightly to the right of the line made by the first two. So if you put the vertical reticle through the dots that would give you a little cant, if the paper they're on was just a little crooked that could be a little more, etc. Putting them so you know they're straight will eliminate that as a variable next time. You might want to try a line or smaller dots that'll give you less fudge room lining up the reticle through them. Good luck. It sounds like you're well on your way. Eliminate one thing at a time and eventually everything will be working 100%. Shooting at long range is fun and the extended capability it gives you while hunting is valuable, but it's not forgiving. There are a million things that can go wrong when you pull the trigger, but only one way for it to all go right. |
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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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Sakomato,
Here is an interesting article on the impact scope cant has on your shot:
22 Long Rifle and the Effect of Scope Cant
Scope what? Scope Cant describes the tipping or tilting of the rifle and scope to one side or the other of verticle. Very small devaitions from straight up make surprisingly large changes to impact point. To find out just how large, I once again turned to Jim Ristow's Gun Controller V2.2.8. The Exterior Ballistics portion of Gun Controller has a function that allows introduction of a sight cant error. Sight cant is measured in degrees, with 6 degrees equal to the slant of the minute hand as it points to 12:01 on an old style analog clock. One minute of tip isn't much, and it would be easy to miss it when looking through the cross hairs, especailly if there were no horizontal or vertical references visible. Table 1 shows that the bullet starts off .16" to the left of the line of sight, just as you would expect if the scope was tipped to the right. The bullet crosses the line of sight at about 30 yards, and by the time it arrives at 50 yards, its 1/4" right of the aiming point.
Figure 1 shows the plot of the deflection data from Table 1.
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Hell, somebody already figured this out
I wasn't crazy after all!
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Guns only have 2 enemies, rust and politicians
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mercenary1947
Optics Master ** Joined: April/02/2006 Location: United States Status: Offline Points: 1392 |
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Great link ..... and man I'd love to borrow that dog for a day .... does he do legs ? Boy have I got a few people here I'd love to introduce him to !
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One Shot One Kill .... *S.O.F * Head Shots Only
SWFAM |
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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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I re-read the article. I then cut out a circle and drew a reticule on it giving me a "scope". I then zeroed my "scope". I then drew the t-line as suggested. With a deliberately canted "scope" I dialled up, meaning the crosshair moves down and to the right of perpendicular. I know aim at the same point as my first "bullet hole", still with the same cant on the "scope". The new impact point shows to the right of the perpendicular. I then align the scope with the horizontal as stated by the article by turning the rifle . The new Point of Impact shows back exactly on the perpendicular (not left or right). All I have done is effectively canted the rifle under the scope to compensate for the scope cant. At 100 yds I say the cant will not show up if it was a real situation (or am I mistaken). In other words the article is assuming that a canted rifle will shoot left or right at 100yds.
I say that the only way to test it is to first level the rifle whilst aiming at the bullet hole, then to keep the rifle absolutely still whilst dialling up or down and to see whay your crosshair is doing.
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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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This is why a canted scope makes very little difference at short distances (300yds?) as the shooter simply cants the rifle to compensate for a canted scope. In other words the shooter will automatically level the reticule by slightly canting the rifle.
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rkingston
Optics Apprentice Joined: February/29/2008 Location: Junction, Tx. Status: Offline Points: 97 |
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From 8 shots: I say that the only way to test it is to first level the rifle whilst aiming at the bullet hole, then to keep the rifle absolutely still whilst dialling up or down and to see whay your crosshair is doing.
This is correct. While that "T" test is one method of checking, it isn't perfect. The scope doesn't really care what position the rifle is in when it comes to tracking. If the scope was slightly rotated and you perfectly lined up the vertical crosshair of the scope to the corner of a square building and turned the elevation turret, it would still track in line without any deviation. I think the only time this situation could turn out to be a real problem would be with a multi-zero scope like Sakomato's where you are moving the elevation turret to extremes. Level the rifle, level the scope, level the target. Crank the elevation up and down to make sure it tracks on the vertical axis. Done. I'll test this soon as I just bought one of the Kahles MZ's for my .280.
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sakomato
Optics Master Joined: February/28/2008 Location: Houston Status: Offline Points: 1166 |
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Yes, essentially you would be holding the verticle reticle straight up and down and canting the rifle. An extreme example would be turning the rifle on it's side and using the windage turret as the elevation turret. The point of impact of the rifle would still move up and down on the vertical even though the rifle had a 90* cant on it.
The problem would really exhibit itself if you are not holding the vertical reticle perfectly straight up and down. Then it would not matter if the rifle were canted or not, the points of impact would progressively move off vertical.
Now if you had a reticle that was perfectly aligned with the bore and canted the rifle then you would be doing the same thing, the POI's should move off the vertical. That's why I have come to the conclusion that the anti-cant bubble on the scope is important.
I'm not convinced of that. I have several rifles with an internal ballistic reticle like a RapidZ 800 and in my extreme example if I mounted it so that the vertical reticle with the ranging marks were straight out to the side, then by moving the point of aim down the reticle to one of the range mark, say the 600 yard mark, I would then be moving the point of aim to the right just like with a cranking elevation turret. Right? Somebody help me, I'm going crazy.
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Guns only have 2 enemies, rust and politicians
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