GTA
Support Equipment For PCP/HPA/CO2 and springers ,rams => Optics, Range estimation & related subjects => Topic started by: RAJOD on June 16, 2017, 01:22:35 AM
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I was looking at all these leveling devices for scopes and thinking that its almost impossible to get a scope on a gun perfectly. Yet my guns shoot pretty good and I'm just keeping the scope level knowing that the barrel under it might be off a little.
- When you level the gun you are assuming.
1. That the top of the gun breach is actually level and perfectly aligned with the barrel under it. Even if the level is perfect (many small ones are not) the top of the receiver might be out of line with the barrel in some way (Up, down, left or right)
2. That the top of the Scopes cap is really aligned with the cross hairs. (its close but not always aligned)
Seems all these errors can add up to a mess but it does not seem to .
This article explains why a little can't error is not as bad as it seems. Keep the scope level is all you need to do.
Take a look see what you guys think.
https://bangsteel.wordpress.com/2013/05/19/canted-scope-or-canted-rifle-the-difference/
I think maybe the best way is to trust that the top of the gun is somewhat true. Then use a level and lock it in vise leveled.
Then mount the scope and level just the scope with a plumb line. DONE. Then just adjust windage and elevation shooting from a bench.
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Rajod,
If you are only shooting at one range and zero at that range scope cant will not be an issue. Once you start shooting at different ranges, keeping your scope zero the same, I find it hard to believe that they say the poi error from the poa remains the same 1/4 inch for example at all ranges and tracks along the vertical reticle. That error has to grow as range increases or decreases from scope zero.
I one example he even shows a barrel that shoots to the right parallel to the scope cant. Come on! When does that happen in the real world lol?
Taso
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I put a small bubble level on a flat part of the reciever ( if possible ). I also put one on the top scope turret at the same time, and hope for the best.
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I attached a small magnet to the bottle of tge bubble levels.
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I was looking at all these leveling devices for scopes and thinking that its almost impossible to get a scope on a gun perfectly. Yet my guns shoot pretty good and I'm just keeping the scope level knowing that the barrel under it might be off a little.
- When you level the gun you are assuming.
1. That the top of the gun breach is actually level and perfectly aligned with the barrel under it. Even if the level is perfect (many small ones are not) the top of the receiver might be out of line with the barrel in some way (Up, down, left or right)
2. That the top of the Scopes cap is really aligned with the cross hairs. (its close but not always aligned)
Seems all these errors can add up to a mess but it does not seem to .
This article explains why a little can't error is not as bad as it seems. Keep the scope level is all you need to do.
Take a look see what you guys think.
https://bangsteel.wordpress.com/2013/05/19/canted-scope-or-canted-rifle-the-difference/ (https://bangsteel.wordpress.com/2013/05/19/canted-scope-or-canted-rifle-the-difference/)
I think maybe the best way is to trust that the top of the gun is somewhat true. Then use a level and lock it in vise leveled.
Then mount the scope and level just the scope with a plumb line. DONE. Then just adjust windage and elevation shooting from a bench.
Humm.......seems that these shooters disagree............
http://www.airgunnation.com/topic/effects-of-rifle-cant-at-50-yards/ (http://www.airgunnation.com/topic/effects-of-rifle-cant-at-50-yards/)
http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/ (http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/)
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I'm a firm believer in cant being a big issue. Do the test yourself and you'll see.
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As stated above, it may not be as big an issue at a single range or over very limited range. Once you start shooting at varying distances and especially at long ranges it becomes a major influence on ability to hit a target. Even though air guns are shot at shorter ranges than firearms, we typically shoot at relatively small targets so the concept is quite similar and probably just as important.
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Right bandg. Also since our pellets have low BC's the effects are amplified for the worst. Powder burner bullets with their high BC's are affected less.
Taso
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Lots of good info thanks guys.
Even if can't errors can be a big deal. Even Vortex admitted the top of the elevation cap is not true to the cross hairs and some scopes have rounded caps etc. Then you get to the guns receiver if the dovetails are perfectly aligned then then is the barrel really perfectly aligned etc. Lots of small errors can add up. I don't see a sure fire perfect way to level a gun.
So for now I just trust the top of the gun to be square level it then use a plumb line (not the top of the scope cap) to level the scope cross hairs.
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I was looking at all these leveling devices for scopes and thinking that its almost impossible to get a scope on a gun perfectly. Yet my guns shoot pretty good and I'm just keeping the scope level knowing that the barrel under it might be off a little.
- When you level the gun you are assuming.
1. That the top of the gun breach is actually level and perfectly aligned with the barrel under it. Even if the level is perfect (many small ones are not) the top of the receiver might be out of line with the barrel in some way (Up, down, left or right)
2. That the top of the Scopes cap is really aligned with the cross hairs. (its close but not always aligned)
Seems all these errors can add up to a mess but it does not seem to .
This article explains why a little can't error is not as bad as it seems. Keep the scope level is all you need to do.
Take a look see what you guys think.
https://bangsteel.wordpress.com/2013/05/19/canted-scope-or-canted-rifle-the-difference/ (https://bangsteel.wordpress.com/2013/05/19/canted-scope-or-canted-rifle-the-difference/)
I think maybe the best way is to trust that the top of the gun is somewhat true. Then use a level and lock it in vise leveled.
Then mount the scope and level just the scope with a plumb line. DONE. Then just adjust windage and elevation shooting from a bench.
Humm.......seems that these shooters disagree............
http://www.airgunnation.com/topic/effects-of-rifle-cant-at-50-yards/ (http://www.airgunnation.com/topic/effects-of-rifle-cant-at-50-yards/)
http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/ (http://www.accurateshooter.com/optics/canting-effect-on-point-of-impact/)
I read the first one and it is different from what the first article says. What the article I put was saying is that if you have a little can't error but you keep the scope "Level" and rezero it it won't make a big difference.
In the first article they simply tilted the gun 20 degrees left or right without keeping the scope level nor did they rezero it. That will show an error because they did not have the cross hairs vertical they tilted both the gun and scope together which gave the expected result. So that article shows a different example of can't not the same as the one I linked. They both agree that keeping the scope level is key.
That vortex scope level is a a good idea. He used 20 degrees can't to make a point. Without a level there is no way I would ever have my scopes cross hair off by that much. More like 1-2 degrees tops which would be more like 1/2-th to 1/10th of an inch off not the 1" he got by using 20 degrees.
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As a serious Air Gun FIELD TARGET competitor .... Cant is very real and worthy of ones attention in minimizing it.
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As a serious Air Gun FIELD TARGET competitor .... Cant is very real and worthy of ones attention in minimizing it.
Thanks motor. Curious what tricks you use to get rid of it, or how you true up a scope on a new gun.
Thanks
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I've personally never used a level, I'm not what ya call a paper puncher, basically I just eyeball the level of my crosshair and adjust from there ??? Even with my Mrod at 80 yards it amazes me just how accurate this gun is and in all reality I don't feel the need for a level at the moment. I plink once in a great while over at my brothers just for a little fun competition and he basically eyeballs his scopes too.
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I've personally never used a level, I'm not what ya call a paper puncher, basically I just eyeball the level of my crosshair and adjust from there ??? Even with my Mrod at 80 yards it amazes me just how accurate this gun is and in all reality I don't feel the need for a level at the moment. I plink once in a great while over at my brothers just for a little fun competition and he basically eyeballs his scopes too.
You can come pretty close just eyeballing it. I once used a level that either the cap was off or the scope was off. Even though it was level on the cap when I looked through the scope it was like 4 degrees tilted.
Now I just look at a plumb line to level the cross hairs.
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Midway sells this gizmo obstansibly made by Weaver:
http://www.midwayusa.com/product/143387/weaver-modular-scope-level-system (http://www.midwayusa.com/product/143387/weaver-modular-scope-level-system)
I am sure others sell it too.
I use this thing.
(http://i1356.photobucket.com/albums/q733/barnydaddy/f981feaf66d0762a20a59c17124d7577_zps5crrejw7.jpg)
You can see how it works.
Metal bar above the receiver (flat part or in a slot), rubber band under the receiver.
Look through the scope and align the cross-hairs with the lines.
The first of these had no level on them.
This is the MK-II version.
Throw it in your kit and you can check the alignment anytime.
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Here is a thread on scope cant by Scotcmo:
https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0)
Using his mirror method should reduce most cant error. To eliminate all error, after using the mirror method make sure your scope vertical reticle is aligned with the point of impact at the apex of pellet trajectory. Then you would have to shoot at different ranges closer and further than the apex of your pellet trajectory and then make small adjustments to scope rotation.
Unless a manufacturer states that any part of the rifle is trued to the bore you are only assuming. Also it is possible that the bore of your barrel was drilled off center, even the most minute amount. Shooting groups on the near and far side of the pellet trajectory apex will show you what scope rotations adjustments need to be made after you've aligned your vertical reticle to the pellet trajectory apex poi.
Thanks,
Taso
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Midway sells this gizmo obstansibly made by Weaver:
http://www.midwayusa.com/product/143387/weaver-modular-scope-level-system (http://www.midwayusa.com/product/143387/weaver-modular-scope-level-system)
I am sure others sell it too.
I use this thing.
(http://i1356.photobucket.com/albums/q733/barnydaddy/f981feaf66d0762a20a59c17124d7577_zps5crrejw7.jpg)
You can see how it works.
Metal bar above the receiver (flat part or in a slot), rubber band under the receiver.
Look through the scope and align the cross-hairs with the lines.
The first of these had no level on them.
This is the MK-II version.
Throw it in your kit and you can check the alignment anytime.
I have one of those. Its not bad, but I'm thinking of getting a level that is attached to my scope.
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Here is a thread on scope cant by Scotcmo:
https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=72099.0)
Using his mirror method should reduce most cant error. To eliminate all error, after using the mirror method make sure your scope vertical reticle is aligned with the point of impact at the apex of pellet trajectory. Then you would have to shoot at different ranges closer and further than the apex of your pellet trajectory and then make small adjustments to scope rotation.
Unless a manufacturer states that any part of the rifle is trued to the bore you are only assuming. Also it is possible that the bore of your barrel was drilled off center, even the most minute amount. Shooting groups on the near and far side of the pellet trajectory apex will show you what scope rotations adjustments need to be made after you've aligned your vertical reticle to the pellet trajectory apex poi.
Thanks,
Taso
Thanks Taso!
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I was going to start a new thread but since this all falls under can't errors I'll just post it here.
Any of you try a tube mounted scope level like these? If you have tried more than 1 which do you prefer. The tall one seems like it could knocked out of alignment easier. The vortex looks decent.
(http://puu.sh/wmGvN/2dfea1ca54.jpg)
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Before I knew anything about scope cant I bought a scope level that mounts to the dovetail. It was monkey see monkey do. I didn't understand what was going on but it was a start lol.
Like everyone else the level tube fell out but was able to find it and epoxy it in place lol.
Scope tube mounted is definitely the way to go.
Taso
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Pyramyd Air has 1 inch and 30mm scope mounted levels made by BKL. They are very well made and can be configured on multiple ways for visibility. $33.95, but to the field target shooter, worth it.
BKL 12-way Scope Bubble Level
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Scope cant...
I am not sure about air rifles but ALL powder burner rifles have their barrels pointed a bit up. A bullet or a pellet begins to drop as soon as it leaves the barrel and is effected by gravity. Rifle makers are aware of this and give the projectile a running start by fixing the barrel with a small amount of upward angle. Thus the apex of the bullet's travel to the target.
If your barrel was perfectly level and you canted the scope (turned the barrel to counteract the cant) then your shot would just go left or right depending on the cant of the scope.
Because of the way the barrel points up, now the projectile will not only be thrown right or left it will also be thrown up in the same direction.
Our brothers and sisters who shoot in three gun competitions have sometimes put a red-dot scope on the side of their main optical scope for close shots. The optical scope is aligned with the bore. The red-dot will not be, so they must shoot the through the red dot with the arm held as normal and not turn the rifle to shoot through the red dot as if it was on the top of the arm. If they do, they will throw the projectile left/right and upward away from the target.
I hope that was not confusing.
But...It is absolutely required that there be no cant in your scope.
Your eye will always try to make the cross-hairs level and you will not be able to do it exactly every time.
Stay safe
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Without a doubt the most noticeable misalignment for me comes from using 3/8" rings on an 11mm dovetail.
Everything else I can correct as I notice it.
If I were a serious competition shooter, as in I paid an entry fee to compete, I'd surely purchase the correct rings.
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Since I have leveled and added a level to my long range shooting guns my groups have significantly tightened up. I am a true believer in making certain my rifle is not canted when shooting. I have one of the BLK levels that swing in and out so it can be swung in when I put the rifle away, then out again when shooting. There have been more than one occasion that my eyes "said" it was level then I look up at the level and I'm over half a bubble off plumb. For long range shooting canting is very important IMHO Happy Shooting!
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I put a bubble level on the breech then hang a string and align the vertical cross hair with that. I figure for my shooting that is close enough
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Geoffrey,
We have been hanging a rock from the 100 yard target stand for years and years.
It works perfectly as long as the stock of the gun is level and supported front and rear on a bench.
IMHO
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Without a doubt the most noticeable misalignment for me comes from using 3/8" rings on an 11mm dovetail.
Everything else I can correct as I notice it.
If I were a serious competition shooter, as in I paid an entry fee to compete, I'd surely purchase the correct rings.
It seems the dovetails can range in actual size from 9.5 to 12mm+. Many rings will say fits both.
ie.
(http://puu.sh/wn84D/2d2fd45cf1.png)
Are you saying these one size fits all both cause issues?
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Pyramyd Air has 1 inch and 30mm scope mounted levels made by BKL. They are very well made and can be configured on multiple ways for visibility. $33.95, but to the field target shooter, worth it.
BKL 12-way Scope Bubble Level
Thanks! Only thing about that level is the screws appear to be UNDER the straps, guess I would have to see it on a actual gun but looked like it would be hard to tighten them.
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Without a doubt the most noticeable misalignment for me comes from using 3/8" rings on an 11mm dovetail.
Everything else I can correct as I notice it.
If I were a serious competition shooter, as in I paid an entry fee to compete, I'd surely purchase the correct rings.
It seems the dovetails can range in actual size from 9.5 to 12mm+. Many rings will say fits both.
ie.
(http://puu.sh/wn84D/2d2fd45cf1.png)
Are you saying these one size fits all both cause issues?
The 3/8 rimfire rings that I use most often fit. But the scope sits a little off to one side with rings that are fixed on one side and have a screw down clamp on the other.
I'm not sure about the ones you referred.
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Without a doubt the most noticeable misalignment for me comes from using 3/8" rings on an 11mm dovetail.
Everything else I can correct as I notice it.
If I were a serious competition shooter, as in I paid an entry fee to compete, I'd surely purchase the correct rings.
It seems the dovetails can range in actual size from 9.5 to 12mm+. Many rings will say fits both.
ie.
(http://puu.sh/wn84D/2d2fd45cf1.png)
Are you saying these one size fits all both cause issues?
The 3/8 rimfire rings that I use most often fit. But the scope sits a little off to one side with rings that are fixed on one side and have a screw down clamp on the other.
I'm not sure about the ones you referred.
Yea that makes sense. I think it might be just easier for companies to make a one size fits both knowing the scope could be off a little from dead center. Most of mine are the side clamping type and maybe my scopes are off +- 1 mm because of that. Not really a can't error but an error none the less.
I'm guessing only the better airguns dovetails are true and actually measure 11mm. I'll have to measure mine and see.
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I've personally never used a level, I'm not what ya call a paper puncher, basically I just eyeball the level of my crosshair and adjust from there ??? Even with my Mrod at 80 yards it amazes me just how accurate this gun is and in all reality I don't feel the need for a level at the moment. I plink once in a great while over at my brothers just for a little fun competition and he basically eyeballs his scopes too.
You can come pretty close just eyeballing it. I once used a level that either the cap was off or the scope was off. Even though it was level on the cap when I looked through the scope it was like 4 degrees tilted.
Now I just look at a plumb line to level the cross hairs.
This^
The farther the distance or greater the holdover, the more it matters.
But as you and others noted, you can get super close by eyeball. Then zero near and far, because that is the real test anyway.
In construction, look down a line of columns you are plumbing up, look up a column at brackets you tacked in for conduit... I can tell which one is 1/2" off from 30 yards or so, even before the theodolite. Your mind/eye connection is designed to be pretty precise.
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I've personally never used a level, I'm not what ya call a paper puncher, basically I just eyeball the level of my crosshair and adjust from there ??? Even with my Mrod at 80 yards it amazes me just how accurate this gun is and in all reality I don't feel the need for a level at the moment. I plink once in a great while over at my brothers just for a little fun competition and he basically eyeballs his scopes too.
You can come pretty close just eyeballing it. I once used a level that either the cap was off or the scope was off. Even though it was level on the cap when I looked through the scope it was like 4 degrees tilted.
Now I just look at a plumb line to level the cross hairs.
This^
The farther the distance or greater the holdover, the more it matters.
But as you and others noted, you can get super close by eyeball. Then zero near and far, because that is the real test anyway.
In construction, look down a line of columns you are plumbing up, look up a column at brackets you tacked in for conduit... I can tell which one is 1/2" off from 30 yards or so, even before the theodolite. Your mind/eye connection is designed to be pretty precise.
Taso had linked a thread on using a mirror and just aligning the vertical line of the cross hairs with the center of the barrel and geometric center of the objective.
I checked two of my guns this way and one was spot on perfect and other might be a tiny bit off. Its really hard to eyeball if the line is exactly centered on the objective. Maybe outside in better light, inside it was a little tricky.
The nice thing about the mirror method is it does away with the level used to level the gun, the one on top of the breach (not scope). Depending on the situation once the barrel and scope are aligned then you have to put on a scope level as you might have to tilt the rifle a little left or right and only a scope level will tell you if everything is lined up.
I pretty much eyeballed those two guns too. I tried that rubber-band scope level and it seemed to introduce inaccuracies.
But yes shooting is the real test and have to do it on a calm day at multiple distances.
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Posted errantly in scotchmos thread.
Not sold on BKL rings. 3 reasons.
1) a clamped ring will only be what 1/32" or 1/64" off ctr? So if you zero for say 50yds, @ 25yds your POI is a whopping 1/90" off ctr? Maybe if you are building a 1000 yard rail gun, for the rest of the world, including actual snipers, it isn't anything to consider.
2) because you are using the ability or lack of aluminum to bend, you can't get actual low scope rings, if you are like me and like a low sight height over bore without a ton of magnification or large objective lense, they aren't great. Also on a stock 13xx platform, the gun has a hard time getting the pellet that high in the first place.
3) I think the real point was labor costs are saved as nobody has to assemble the thru bolt and clamp on the assembly line. But good on them for inventing a problem that didn't exist to push product. Capitalism 101, freedom to market, freedom for me to see threw it.
Not saying they aren't a good product, just saying don't drink the koolaid.
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Sam,
I agree. I am not convinced of the BKL design that "should" self center by bending in the areas that the material has been removed. One side may come toward the center compared to the other. Also the removed material makes the ring weaker in that spot so if bumped will go out of alignment easier.
The Millett Steel Angle-Loc Tip-Off rings may be the most centerable ring that I know of but probably not the easiest to get on center. lol
Taso
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Posted errantly in scotchmos thread.
Not sold on BKL rings. 3 reasons.
1) a clamped ring will only be what 1/32" or 1/64" off ctr? So if you zero for say 50yds, @ 25yds your POI is a whopping 1/90" off ctr? Maybe if you are building a 1000 yard rail gun, for the rest of the world, including actual snipers, it isn't anything to consider.
2) because you are using the ability or lack of aluminum to bend, you can't get actual low scope rings, if you are like me and like a low sight height over bore without a ton of magnification or large objective lense, they aren't great. Also on a stock 13xx platform, the gun has a hard time getting the pellet that high in the first place.
3) I think the real point was labor costs are saved as nobody has to assemble the thru bolt and clamp on the assembly line. But good on them for inventing a problem that didn't exist to push product. Capitalism 101, freedom to market, freedom for me to see threw it.
Not saying they aren't a good product, just saying don't drink the koolaid.
I found the BKL design to be no more useful than a cheap UTG mount, and in some cases more damaging to scope tubes. Here are a couple other issues I had when using the "two piece double strap" mount.
BKL gives the max screw torque for the horizontal base screws as 35in/lbs, they list no maximum torque for the screws of the narrow "top straps". Here are a couple pics of scope tube damage using a standard 15in/lbs of screw torque and scope slippage using only 10in/lbs screw torque. Notice the distinctive "double strap" dents........
Scope creep when using only 10in/lbs of top screw torque.........
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/BKLMounts.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/BKLMounts.jpg.html)
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/10InLbsScopeCreep.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/10InLbsScopeCreep.jpg.html)
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/PinchedScopeTube.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/PinchedScopeTube.jpg.html)
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/CPdamageBKL.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/CPdamageBKL.jpg.html)
Now concerning the BKL one piece mount, I had no issue with scope tube damage using 15in/lbs of torque on the wider single top straps, but I did have scope and mount slippage issues until I did a couple mods.........
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/ScopeShiftBKL.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/ScopeShiftBKL.jpg.html)
My solution for the BKL issues I had mounting a scope on my de-tuned twang/vibration free R9 were.........
Don't use the two piece "double strappers" at all and there must be some reason that BKL came up with these "gems"..........
(http://img.photobucket.com/albums/v734/wved/Scopes_Mounts/BKL-1in-Triple-Strap-High-DT-Single_BKL-S264H-MB_lg.jpg) (http://smg.photobucket.com/user/wved/media/Scopes_Mounts/BKL-1in-Triple-Strap-High-DT-Single_BKL-S264H-MB_lg.jpg.html)
The one piece BKL mounts worked OK and the scope and mount didn't slip after after a couple mods.
First was to line the top and bottom half of the rings with cloth electrical friction tape which stopped scope sliding with 12in/lbs of top strap screw torque.
To stop scope mount sliding on the receiver dovetail the first thing I did before mounting the mount was to "pre-spring" the base "claws" by tightening all base screws till the "claws" wouldn't slide on the R9 dowetail after all screws were loosened. Then I removed one of the base screws, inserted it in one of the provided "spreader holes", tightened this screw just enough to spread the "claws" so the mount would just slide on the receiver dovetail, position the mount and remove the screw from the spreader hole. LOL......after removing the screw from the spreader hole the "spring back" was great enough that the mount couldn't be moved by hand even with all screws loose. The final step was to torque all base screws to 35in/lbs and then the one piece BKL "stayed put" when shooting even with a rather heavy 3-12x44 Optisan Viper mounted. Actually, too much hassle for my taste!
I still have the BKL one piece mount (tossed the two piece "double strappers" but I prefer the cheap UTG/Leapers mounts with the wide 4 screw top straps since I've never damaged a scope tube using them and I really haven't found any "cant issues" when using the "clamp plate" style mounts If I level the top of the R9/HW95 barrel pivot block and then align the reticle with a hanging string at 18 yards ((barrel bent to accommodate the optically centered scope).
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Frank, if you can hit exactly where you aim at some distance with a scope on an air rifle then by simple physics the barrel has to be "pointed up" in relation to the line of sight through the scope. Cannot be otherwise or the pellet would always hit low at every distance so whether a droop mount is used or internal correction in the scope, the line of sight and line of bore must be converging to be able to hit exactly on a small target. How high above the bore the scope is mounted and what zero concept is used will determine how much the ballistic arc rises above line of sight (if any).
The mirror method sounds logical but the only method that I have ever been able to use with confidence to be assured that my "scope" is level with my "rifle" is to put verified level horizontal and vertical lines (use an actual level and a square) across my target dot to be certain I am holding the scope perfectly level and then crank elevation up and down while firing. The point of impact will rise and fall but if the "scope and rifle" (mounts, dovetails, receiver, square, not square, whatever) are in the same vertical plane then the point of impact will stay on the vertical line no matter how high or low it goes. This does require a calm day as you must be confident that wind drift is not a factor but it does physically match the ballistic arc of the projectile to the internal elevation function of the scope (which as noted above may not always match the external appearance of the scope/mount/rifle, etc.
Only once I have done the above do I install and rely on any bubble level or similar. I may be wasting my time doing all this but for all my long range firearms (and seemingly any air rifle with a ballistic arc that is relatively extremely curved even though more difficult due to wind effects) I've found it to be a totally reliable method.
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some might think its over the top but most scope rings probably need lapping or ring friction tape to keep the pressure even and prevent denting.
https://youtu.be/fTIY9cZlpPs
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Burris makes dovetail rings with a synthetic insert that works like a spherical bearing that auto aligns and relieves any stress. Pretty cool I think.
http://www.opticsplanet.com/burris-airgun-rimfire-signature-1-rifle-scope-mount-rings.html (http://www.opticsplanet.com/burris-airgun-rimfire-signature-1-rifle-scope-mount-rings.html)
They are also supposed to come with an 11mm clamp which may help the ring grip better but there is a small dimensional difference between 11mm and 3/8 dovetails. So I don't think the scope will sit perfectly centered with the ring's 11mm and 3/8" compatible interface. So that will also cause the scope to possibly not be in the same vertical plane as the bore.
More stuff to worry about lol.
Taso
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Please note it is not necessary to have the scope perfectly centered above the dovetail. You could have the scope mounted 1 inch off to the side, and so long as you align the reticle to the muzzle and hold the reticle level when you shoot, there will be no cant error whatsoever. It would mean you are holding the stock at what looks like a strange angle, but the gun would exhibit no cant error. So don't be concerned about 11mm or 3/8" dovetails. It does not matter except for visual symmetry.
With that said, let me detail a few points about these two types of dovetails. An 11mm should measure very close to 11mm across the wide part of the rail, normally within 0.1mm or so. A 3/8" dovetail is dimensioned based on the narrowest part of the groove so it's not as easy to measure. A 3/8" groove will usually measure between 12mm and 13mm across at the top so it is usually easy to distinguish by process of elimination. The other difference is that an 11mm dovetail is cut at a 60° angle and a 3/8" is cut at 45° angle.
If you have tipoff rings with reversible clamping plates, they will likely have one tooth with a noticeably shallower angle than the other. That would be the 60° side you want to use for an 11mm rail. Or use the sharper tooth for a 3/8" rail.
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Regarding levels, don't spend your hard earned money on a rail-mounted level. They shouldn't even be sold unless they have some sort of fine adjustment screw for the bubble tube. Why? Because this style attempts to level the receiver. The receiver does not matter. Depending on how everything fits together, the receiver may very well need to be held slightly off level.
What you want to do is orient the vertical bar of the reticle so it simultaneously bisects both the objective bell and the muzzle (looking at your reflection in a mirror as previously described). Then fasten your level so it shows level when the horizontal bar of the reticle is level (or when the vertical bar of the reticle is plumb...whichever one you can do more confidently). To secure the level correctly, you have to be able to adjust it, and one that mounts to the scope tube is easily adjusted. Those that mount to the rail usually cannot be.
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Jason,
I totally agree. ;D
I was just trying to inform those that were leveling against an assumed true squared receiver. All that matters is that we get the scope and bore centerlines in the same vertical plane and be able to repeat that orientation with a properly adjusted scope mounted level. :)
Taso
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Regarding levels, don't spend your hard earned money on a rail-mounted level. They shouldn't even be sold unless they have some sort of fine adjustment screw for the bubble tube. Why? Because this style attempts to level the receiver. The receiver does not matter. Depending on how everything fits together, the receiver may very well need to be held slightly off level.
What you want to do is orient the vertical bar of the reticle so it simultaneously bisects both the objective bell and the muzzle (looking at your reflection in a mirror as previously described). Then fasten your level so it shows level when the horizontal bar of the reticle is level (or when the vertical bar of the reticle is plumb...whichever one you can do more confidently). To secure the level correctly, you have to be able to adjust it, and one that mounts to the scope tube is easily adjusted. Those that mount to the rail usually cannot be.
Yes I like the mirror way as then you don't have think about the level of the gun. But I found it tricky to eyeball in the mirror that my line split the barrel and the large objective exactly. Seems it could be off -+ 1 degree and it would still look 50/50.
I think the idea is to eyeball it in the mirror to be close, but the really dial it in you need to shoot at two distances and see if it hits a plumb line target on both distances.
Have not had time to really test it, only done the mirror part.
Also the real reason people have to worry about these can't errors is the scope mount height. if it were inside the barrel (Alien tech :) there would be no need
the higher the scope is mounted the worse the errors become.
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Actually if the line of sight were in the barrel, cant error would still be a present because of the pellet's arced trajectory. If the scope isn't held level, the pellet will diverge from the aim points...because it's following the force of gravity.
Unfortunately there are many similar bits of misinformation about scopes that get cited by well-meaning individuals which makes it rather difficult to sort out what is really true. I'm sure I was guilty of it somewhere along the way which is why I usually stop and try to explain when I see them repeated.
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With respect, you are dead wrong here Jason. If line of sight were in the bore there could be NO cant error in any manner. Ballistic arc is always present and always will be for any projectile fired under the influence of gravity and is really totally independent of cant, scope height, or anything else. Ballistic arc becomes involved with cant as the LOS and the bore are separated. If as you state line of sight was in the bore then you could spin the bore 360 and never change anything at all. The cant error is entirely related to some degree of offset (which is there even to a small degree with very low iron sights but becomes worse the more the bore and LOS are separated) between the bore and the line of sight.
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We're both right, we are just talking about two different things. Re-reading my post, I can see that I was not clear enough. Sorry.
The scenario I was trying to describe is holding the reticle canted. In this hypothetical example where the bore and sight are magically on the same axis, they cannot have any misalignment-induced cant...as you correctly state. However, if I hold the reticle canted, the pellet will diverge from the vertical holdover/holdunder points shown on the reticle. Imagine an extreme example where I have canted the reticle 45 degrees clockwise. If I launch a pellet, clearly it will not arc downward and to the left to follow the reticle. It will follow gravity straight down.
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I hope we are on the same wavelength but I'm not certain and I think this may be where many people get very confused about this issue. In your last post above about canting the reticle 45 degrees you note that the pellet will not magically follow the holdover dots and will simply "follow the gravity". Certainly accurate but no one would tilt a reticle 45 degrees unless they have bigger concerns than shooting at a target. But they may tilt it a few degrees without realizing it and this is the problem with cant in that you would probably notice the big amount but maybe not the small amount. And although the pellet will always follow the same ballistic arc (following the gravity) that arc can change relative position (not it's shape) dramatically in relation to line of sight because you have the additional factor of convergence of bore and LOS.
I've dealt with this shooting long range firearms but air guns don't experience it to the same degree due to limited range. Imagine tilting the reticle 5 degrees CW but not realizing it. The bore is now "out to the left" in relation to the vertical LOS plane. But even though the ballistic arc is physically only curving downward as shaped by gravity, IN RELATION TO LOS it is also moving to the right as well (LOS and bore must converge to hit on a zero point). The pellet will move toward the LOS vertical plane and eventually cross it moving away further right. This is not an extreme amount on an air rlfle because we normally shoot at ranges less than 100 yards and most of us well less than that. But for firearms it becomes a major issue as you try to reach further out. The projectile will not only be dropping on its constant physical arc but will be moving further and further right of the vertical LOS plane in the above example.
Now imagine the above issue combined with a changing windage (right to left and then left to right). One shot the wind would be resisting the pellet movement toward the vertical plane and maybe it wouldn't cross it or not by much. The next shot the wind would be aiding the movement and it would cross the vertical quicker and move much further right. This combination is much worse for air guns because of the lower velocity and poor BC of the pellets. This is why I noted above setting up my long range rifles the way that I do and why I even take the time to do it with my air guns. Years ago I spent many hours on the range chasing the above combination of errors until I learned to match the ballistic arc with the plane of scope function (elevation up and down) as exactly as possible first and then set my leveling aid up to that verified level point.
All of this worsens with higher mounting points for the scope (more separation of bore and LOS and thus more convergence angle needed). And even though our air rifles don't function at the same ranges as firearms, generally we expect to hit very small targets so it can be an issue and I believe very much so on more windy days.
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Very well articulated, sir. :)
I think we are on the same wavelength, and I will concede you have broader real-world experience in the way of long range powderburner marksmanship. So can you lend us your perspective on a question? Given the loopy trajectory of a diabolo pellet, doesn't the practical effect of cant manifest at much shorter distances than a high velocity centerfire round?
I think of cant error as being an error of "my reticle predicts the pellet will fall to this point out there at a distance, but gravity means it will actually fall to a slightly different point". So the further out at a distance it goes--and the more the pellet drops--those two points diverge more and more. So I reason a projectile that drops more is in a sense more sensitive to cant error. Is that valid to your understanding?
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Why would you tilt an arm 45 degress in one direction when you could easily tilt it 15 degrees the other way?
Time to return to your video games, I am thinking... >:(
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I'm half gangsta, nuff said.
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Not as I understand it. The cant error must be separated from gravity even though both effect the shot. The ballistic arc is relatively constant and always curves with the direction of gravity but the cant error can change in both direction and subtle degree. It is a related but independent parameter. Consider again the 5 degree CW cant and assume it moves the bore 1/4" left from vertical. Zero is probably 25 yards for many of us so bore and LOS converge at that point and the pellet will be on the vertical at that range (it would be a little lower than you would expect because the cant lessens the angle of rise a bit as well so that is another complication but probably negligible). 25 yards beyond zero range (assuming no wind effect) the pellet would only be 1/4" off from vertical to the other (right) side but again lower than you would expect. But how many of us shoot beyond 50 yards regularly? That is why I think it is less of an issue for an air gun as it is an error that continually increases with distance. At 100 yards the pellet would be 3/4 inches right of vertical LOS (it moves roughly 1/4" for each 25 yards unless I'm off on this since I haven't done the math) but again even lower than you would expect. Take this out to 600 yards and realize you could make the error to either side and you have basically a foot of "slop" in the shot under ideal conditions. Add in any windage effects and you have not only a larger range of error but also the unpredictable adding and subtracting of the windage effect I mentioned in the above post. I certainly believe that the windage effects would be much greater for the pellet than for a firearm bullet (and generally worse for 177 than 22, etc.) due to velocity and BC and would almost certainly have a large impact on air gun pellets within their normal range but I don't believe it would ever overcome the range component. I enjoy discussing such issues but it's been a long day and I could have some of this wrong but I think I have these concepts correctly laid out.
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Here are all the possible combinations of scope cant and rifle cant.... Scope cant is measured relative to the rifle.... Rifle cant is measured relative to a plumb line (ie gravity)....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/ScopeCantChart_zps994cd58d.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/ScopeCantChart_zps994cd58d.jpg.html)
In the diagram below, "A" is the most common error made in mounting a scope.... "A" only works if the scope is centered over the bore (almost never happens!) when both are level....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/Scope%20Cant%20Fix_zpsjtlvn6gb.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/Scope%20Cant%20Fix_zpsjtlvn6gb.jpg.html)
If the scope is not centered over the bore, then you must twist the scope as in "B" so that the vertical crosshair aligns with the bore (this is where the mirror helps).... You then hold the rifle as in "C" to eliminate all cant errors.... The pellet rises and falls vertically, under the effect of gravity, starting from the muzzle.... Only if the crosshair lines up with the barrel, and is also held vertical, does the pellet path track perfectly along the vertical crosshair....
until you add wind.... ::)
Bob
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Actually if the line of sight were in the barrel, cant error would still be a present because of the pellet's arced trajectory. If the scope isn't held level, the pellet will diverge from the aim points...because it's following the force of gravity.
Unfortunately there are many similar bits of misinformation about scopes that get cited by well-meaning individuals which makes it rather difficult to sort out what is really true. I'm sure I was guilty of it somewhere along the way which is why I usually stop and try to explain when I see them repeated.
:) Can't error can only happen if you have a scope mounted on the barrel not inside it. Its round so even upside down the line of sight would be centered, gravity would play the same role in all positions. But as you know that example I gave was in fantasy land. :)
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Here are all the possible combinations of scope cant and rifle cant.... Scope cant is measured relative to the rifle.... Rifle cant is measured relative to a plumb line (ie gravity)....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/ScopeCantChart_zps994cd58d.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/ScopeCantChart_zps994cd58d.jpg.html)
In the diagram below, "A" is the most common error made in mounting a scope.... "A" only works if the scope is centered over the bore (almost never happens!) when both are level....
(http://i378.photobucket.com/albums/oo221/rsterne/Important/Scope%20Cant%20Fix_zpsjtlvn6gb.jpg) (http://s378.photobucket.com/user/rsterne/media/Important/Scope%20Cant%20Fix_zpsjtlvn6gb.jpg.html)
If the scope is not centered over the bore, then you must twist the scope as in "B" so that the vertical crosshair aligns with the bore (this is where the mirror helps).... You then hold the rifle as in "C" to eliminate all cant errors.... The pellet rises and falls vertically, under the effect of gravity, starting from the muzzle.... Only if the crosshair lines up with the barrel, and is also held vertical, does the pellet path track perfectly along the vertical crosshair....
until you add wind.... ::)
Bob
Yes thanks Bob. I was looking at that, "Taso linked it" I like it.
Is the most common error due to the dove tails not being centered exactly? Or is it due to scope rings pushing the scope to one side a little.
I read you had a few guns that failed on the mirror test. I think you said that one shot left near and right far or something like that. When you centered the barrel/objective via mirror did it correct those issues?
Also did what distance did you find it easiest to line up the barrel with objective. I tried in my house at 10 meters from the mirror and I found it a little tricky to know for sure if I bisected that objective 50/50. Probably due to less than perfect lighting.
Thanks!
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Regarding levels, don't spend your hard earned money on a rail-mounted level.
Because this style attempts to level the receiver. The receiver does not matter. Depending on how everything fits together, the receiver may very well need to be held slightly off level.
Agree with you there. But only to that point. I have used rail mounted and scope mounted (have one of each on two different guns).....
I used 5 or six levels when I set the gun up. on the rest, on the receiver on the scope and any where else I can find something level (and if a magnet sticks to it, bonus...), have a Wheeler leveling kit for the barrel..... I work them all until they are all in alignment bubble-wise or a majority of them show the same thing.
back to the rail mount, when the scopes shows itself to be level, thats when I put on or adjust the rail mount. and adjust it against known square/level objects. That becomes field level indicator. Rail mounted levels are fine IF you understand where they can be wrong, and what they are "calibrated" against .
I agree though, just clamping one on wont get you much
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Yes, using a mirror to align the vertical crosshair with the barrel fixed the problem.... My Hatsan was the worst, zeroed at 50 yards, it would shoot 2" right at 100 yards, and 1" left at 10 yards before I used the mirror method.... I set the scope for the closest possible focus, increase the magnification to maximum, and then set the mirror at half the closest focus, so that the image of the muzzle and scope objective is clear when I look through the scope.... If the scope is a 4-12 X and focuses down to 10 yards, I use 12X and set the mirror at 5 yards.... Set the rifle in a solid rest, reasonably level (not critical), and rotate the scope in the rings until when you look through it, the crosshair bisects the image of both the objective and muzzle.... then carefully tighten the rings, checking to make sure it didn't change.... Note you should have the scope reasonably close to the optical center BEFORE you do this.... If you have to move the crosshairs over a lot in windage to sight in your rifle, you will be moving the crosshair away from the image of the muzzle if you check it again later.... I have never found I have to fine tune my scope rotation after this, but likely that is because I'm not a good enough shot to tell that the impact is off 2mm at 25 yards and 5mm at 100 yards.... In other words, a carefully done mirror setup during scope installation is all I need.... After that, if I hold the vertical crosshair vertical when shooting, my cant problems are eliminated....
Bob
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Note you should have the scope reasonably close to the optical center BEFORE you do this.... If you have to move the crosshairs over a lot in windage to sight in your rifle,
Bob
Nice, that was my next question, should I reset my scope to optical center. Thanks! I've learned quite a bit on this forum. I really like the mirror trick vs leveling the breach. And it appears to hold up in real world testing.
I am a little amazed that all the searching I did on scopes they mostly eyeballed it or used a level. I was never quite happy with that because of too many assumptions. Many videos the guys just says "I prefer to eyeball it" and no disrespect to them eyeballing it gets the job done to "Good enough" for most. The mirror method goes one step further. Even after I do it all correctly my kid will still outshoot me with an inferior scope/gun and some can't error.
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There is one simple way to completely, 100% eliminate cant error.... Sight your scope in at the distance you are shooting at.... and never shoot closer or further away.... ::)
That will even work for side-mounted scopes like on a 30-30 Winchester that ejects out the top.... 8)
Bob
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There is one simple way to completely, 100% eliminate cant error.... Sight your scope in at the distance you are shooting at.... and never shoot closer or further away.... ::)
That will even work for side-mounted scopes like on a 30-30 Winchester that ejects out the top.... 8)
Bob
That is pretty much what I have been doing in the back yard. I'll do a 50 yard shoot then adjust for that distance and do some great groups. I might not shoot again for a week and it could be at 35 yards and then I'll just shoot a few sighting shots and I'm good again. Never had to really think about can't errors. Just did not have the time to fiddle with it to the level you have done.
I'd sight for 20-25 yards and just worry about hold over. 10 yards 2 mildots or so 25-35 dead on. I had to have been pretty close because I did not stray too much side to side. I think people that shoot bench competition are far more aware of these errors. I'm slowing progressing to that level.