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Gunsmithing Vertical Crosshair to Barrel Bore

ShtrRdy

ShtrRdy

Gunny Sergeant
Full Member
Minuteman
    • Sep 17, 2011
    2,932
    800
    High Plains
    I'm still pretty new with this sort of stuff, but I was wondering how do you ensure the vertical crosshair in the scope is in line with the barrel bore?

    It seems like it's very important for this relationship to be set in order to be able to dial come-ups in a truly vertical direction. I realize that it's important for the scope elevation turret to follow the vertical crosshair as well.

    Thanks - Todd
     
    Re: Vertical Crosshair to Barrel Bore

    Wheeler kit is a good place to start
     
    Re: Vertical Crosshair to Barrel Bore

    Quick easy way I do it is to place a level on my rail, level the gun, carefully place the scope on, place the level on top of the turret.
     
    Re: Vertical Crosshair to Barrel Bore

    ^^^
    Yep.
    Then get a rail or scope (ring) mount bubble level to ensure that the rifle itself is level when shooting...
     
    Re: Vertical Crosshair to Barrel Bore

    If push comes to shove, I don't think that there is any PRACTICAL way to definitvely determine that the vertical stadia is in absolute alignment with the cylindrical axis of the bore.

    It is easy enough to determine if the horizontal stadia is parallel with the "X" axis of the bore, but the "Y" axis alignment is another matter.
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RTK</div><div class="ubbcode-body">Quick easy way I do it is to place a level on my rail, level the gun, carefully place the scope on, place the level on top of the turret.</div></div>

    Hang a string or level at distance, align your crosshairs, and check the turret tops, more often than not you will be really surprised .

    Wheeler kit is good juju, can't go wrong.
     
    Re: Vertical Crosshair to Barrel Bore

    Drop a 30mm (or 1", depending on the ring size), long enough to extend beyond the muzzle, with a hole drilled into 1 end, into the rings. Put on the ring caps, and drop a weighted string from the hole on the end of the rod. Check its alignment with the bore.
     
    Re: Vertical Crosshair to Barrel Bore

    I use this tool. With the scope straight over the bore the rail may have a slight cant to it. That is unimportant. The main thing is the scope is plumb over the bore. Once the scope is over the bore then roll the scope until the crosshairs are plumb with a plumb bob string or known verticle line. With this method I can dial up 45 MOA and still cut a vertical line with my bullets.

    p_289100000_1.jpg
     
    Re: Vertical Crosshair to Barrel Bore

    I wonder if the question asked is:

    Given that the vertical stadia is perfectly perpendicular to the horizontal stadia, how does one determine if the the vertical stadia lies on the exact same plane as the axial bore of the barrel?

    All other things being equal, the bore of the scope could be offset either to the left or right of the bore of the barrel a few thousandths of an inch.
     
    Re: Vertical Crosshair to Barrel Bore

    I wonder if the question asked is:

    Given that the vertical stadia is perfectly perpendicular to the horizontal stadia, how does one determine if the the vertical stadia lies on the exact same plane as the axial bore of the barrel?

    All other things being equal, the bore of the scope could be offset either to the left or right of the bore of the barrel a few thousandths of an inch.
     
    Re: Vertical Crosshair to Barrel Bore

    Ack! Sorry, but I can't resist the urge to point out that the word 'stadia' is plural. The proper usage is: "The stadia are..."

    Stadia are those short lines on a reticle that run perpendicular to the cross hairs dividing them up into distinct units (usually mils for a rifle scope). I've never seen the word used with respect to rifle scopes; only for surveying instruments, and then, most engineers use "stadia mark" to avoid the awkward sounding Latin singular (where the singular, 'stadium', an ancient unit of measure, would sound very awkward indeed).
     
    Re: Vertical Crosshair to Barrel Bore

    http://badgerordnance.com/wp-content/uploads/2012/02/200-50-11.jpg

    I was just down at Badger Ordnance and had this discussion with Marty, and unbeknownsed to me he makes this tool for just this purpose. It's the most accurate way to get it all plumb and true. Think about it you don't know if your turret is inline with your cross hairs, it wasn't too long ago when leupold was sending out optics with canted cross hairs. Also how accurate do you think a torpedo level is. You may think its good but when shooting long distances that fraction of an error multiplies. Give him a shout for for details on how to use this he's a nice guy with a wealth of info. Hope this helps.

    SPM
     
    Re: Vertical Crosshair to Barrel Bore


    The problem is leveling the rifle. We know the two need to be true to each other. You can spend all day leveling your scope with strings and other and gadgets but if your rifle is out a touch you just wasted your time. The way Badger's tool works is you mount your scope on your rifle and adjust the relief you want and just snug the rings on the tube, next take the scope with the mounts off and attach it to the tool. Now level the tool with built in circular bubble level which is more accurate than a torpedo level. Now you can rotate your scope to align your cross hairs to a string, a line you put on the wall with a laser, etc.

    SPM
     
    Re: Vertical Crosshair to Barrel Bore

    How do you get the center line of the scope to match the center line of the bore without re-tapping the receiver? I guess I'm missing something here.

    SPM
     
    Re: Vertical Crosshair to Barrel Bore

    Using the EXD tool you can end up with a slight cant of the receiver to get the scope plumb over the bore. No more "spin drift" at 300-800 yards. This is why we use scope mounted anti cant levels. The ones that mount to the rail need to be shimmed to get them right. Using this method gives us true windage free come ups for long range.
     
    Re: Vertical Crosshair to Barrel Bore

    How are you checking the rail for cant? How are you leveling the rifle before you check the rail for cant? The two must correlate with each other. I can not think of any way to truly plumb or level the center line of a rifle. To me the Badger tool is the closest you will ever get. Good debate.

    SPM
     
    Re: Vertical Crosshair to Barrel Bore

    Put it together and using the EXD tool shown above, we plumb the scope dead nuts over the bore. Then you can check the rail and see it's out of whack. I can also mount the action in my Holland action holding jig in my mill and use a dial indicator on the edges to check for alignment and level. It's fixable. I can dial in off the raceway and can mill out the 6-48 screws and relocate the holes in line and on center with 8-40 screws and get it right on.

    The proof is to site in at 100 yards. Then dial up the scope 30-45 minutes and shoot another group. It should be exactly on line above the first group.

    The average sub 500 yard shooter usually will not notice but we play at 1000+ and it shows up huge if you are not over the bore.
     
    Re: Vertical Crosshair to Barrel Bore

    I must be confused about what is being discussed. Seems to me, If the vertical crosshair is vertical and you crank the elevation up and down and shoot at 100 yds the bullets will be in line regardless of the relationship to the barrel bore.
     
    Re: Vertical Crosshair to Barrel Bore

    If you put it plumb the retical to the rail and the rail is off it will not track with the bore. Means when you dial in elevation correction it will go askew and your point of impact will not be where the retical is pointing.

    This is why many rifles need a windage correction at long range when there is no wind.
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: *Straight Shooter*</div><div class="ubbcode-body">I use this tool. With the scope straight over the bore the rail may have a slight cant to it. That is unimportant. The main thing is the scope is plumb over the bore. Once the scope is over the bore then roll the scope until the crosshairs are plumb with a plumb bob string or known verticle line. With this method I can dial up 45 MOA and still cut a vertical line with my bullets.

    p_289100000_1.jpg
    </div></div>

    This is exactly what I was wondering about. Who sells a tool like this?

    The only other tool I've seen that might to the job is described in an article on Score High Gunsmithing website. Go to http://www.scorehi.com/ then click on Articles and then click on Scope Mounting.
     
    Re: Vertical Crosshair to Barrel Bore

    You're not tracking to the bore, you're tracking the scope and making the reticle plumb with the fall of gravity.

    There are too many issues to say, especially with something resting on the top of the barrel, that the scope is plumb with the bore. Not all barrels are timed correctly so any runout in the bore is not necessarily centered.

    Then you have receiver issues, are the screws lined up exactly square with the bore exit, again, doubtful.

    You simply square the reticle to the fall of gravity, not the exit of the bore.

    There are all sorts of contours and finishes and the bore is not always perfectly aligned to the outside of the barrel.

    It's the fall of gravity, not the bore.
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: *Straight Shooter*</div><div class="ubbcode-body">Put it together and using the EXD tool shown above, we plumb the scope dead nuts over the bore. Then you can check the rail and see it's out of whack. I can also mount the action in my Holland action holding jig in my mill and use a dial indicator on the edges to check for alignment and level. It's fixable. I can dial in off the raceway and can mill out the 6-48 screws and relocate the holes in line and on center with 8-40 screws and get it right on.

    The proof is to site in at 100 yards. Then dial up the scope 30-45 minutes and shoot another group. It should be exactly on line above the first group.

    The average sub 500 yard shooter usually will not notice but we play at 1000+ and it shows up huge if you are not over the bore. </div></div>

    It seem to me that if you sight in at 100 yds, then dial the scope up and ensure you're holding a true vertical, that your shots should impact vertically as long as the scope elevation adjustment is truly tracking the vertical crosshair.

    If the vertical crosshair wasn't in line with the barrel bore, this effect wouldn't show up unless you were shooting at different distances.

    Thanks for the good discussion! It'll be nice to understand this. - Todd
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: *Straight Shooter*</div><div class="ubbcode-body">If you put it plumb the retical to the rail and the rail is off it will not track with the bore. Means when you dial in elevation correction it will go askew and your point of impact will not be where the retical is pointing.

    This is why many rifles need a windage correction at long range when there is no wind. </div></div>

    You missed my point. The reticle can be vertical and still not be centered on the bore. When you crank the elevation up at 100 yards the bullets can track at that distance but shift horizontally when the distance is changed.

    That tool you are saying won't work will work just as well as the one you are using.
     
    Re: Vertical Crosshair to Barrel Bore

    That tool is a waste of money,

    Draw a leveled line on your target and hold the bottom and dial up, make sure the impacts hit the line, or simply drop a string with a weight and make sure the reticle is lined up to the fall of gravity.

    You don't need the scope perfectly centered over the bore, (See M1D) and any little bit you are off won't be noticeable because it will be less than the bullet width.

    Level to the fall of gravity, any level can do it, or a string with a weight
     
    Re: Vertical Crosshair to Barrel Bore

    I use the tool on the bottom of this page. http://www.lyon-inc.com/products/ It works with horizontal split rings and with vertical split rings I run a flat straight piece out leveled across the top of the rail and then set the tool on it. I get the gun level and then line the vertical crosshair up with a string hanging with a weight on the bottom. Seems to get it pretty level.

    Bb
     
    Re: Vertical Crosshair to Barrel Bore

    ScopeSetup.jpg


    Sure, the ideal situation is to have the reticle both level and directly above the bore (A). However, reticle cant (B) is what really kills you, not reticle offset (C). Fortunately, when you have a canted reticle, you can make it level by canting the rifle in the opposite direction. The cant will turn into offset -- situation B becomes situation C.

    As for the error introduced by such an offset, be it introduced while installing the scope, or while compensating for cant? Most of the time, too little to care.

    The error by an offset but level reticle will be just the magnitude of the initial offset times the multiple of the distance the scope is zeroed to.

    ScopeSetup2.jpg


    .1" at 0yd becomes .0" at 100yd becomes .9" at 1000yd. I personally believe I can do better than that when I just remove the bolt, eyeball the reticle to bore relationship, tighten the screws and call it good.

    I obsess more about having the reticle level when I'm actually shooting.
     
    Re: Vertical Crosshair to Barrel Bore

    If people trust that their action base holes are aligned, which I don't, why doesn't someone just make a base like this where you could just bump the threaded riser against the bottom of the elevator housing?

    ScopeBasewithLevelRiser.jpg
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: *Straight Shooter*</div><div class="ubbcode-body">
    The proof is to site in at 100 yards. Then dial up the scope 30-45 minutes and shoot another group. It should be exactly on line above the first group. </div></div>

    Use any trick you can to mount, but the quoted proof above, is the only way to check it.
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">That tool is a waste of money,

    Draw a leveled line on your target and hold the bottom and dial up, make sure the impacts hit the line, or simply drop a string with a weight and make sure the reticle is lined up to the fall of gravity.

    You don't need the scope perfectly centered over the bore, (See M1D) and any little bit you are off won't be noticeable because it will be less than the bullet width.

    Level to the fall of gravity, any level can do it, or a string with a weight </div></div>

    This ^^^. The bullet will always follow the same vertical line in its drop...I guarantee it. And this is why we have knobs on the scope, and why we zero the rifle.

    Again, no fancy tools required (although I confess to owning them)...I make a cursory attempt to level the rifle, and then make sure the reticle is plumb with a distant level or weighted string. I then level the scope bubble...done. While I do not depend on the scope level so much in the field, they are great for reference later on and for that oh so important shot.
     
    Re: Vertical Crosshair to Barrel Bore

    It probably is just picking gnats off an elephant for all diciplines other than maybe benchrest score shooters, but that's why we are here right?
    smile.gif


    The offset is equal to scope hight above bore x Tan(angle of error). So a 1.5" scope height with a 3 degree alignment error will have an offset of .079" or a thousand yard error of .7". I'm pretty sure most of us can eyeball 3 degrees. It's still an interesting topic to me though.
     
    Re: Vertical Crosshair to Barrel Bore

    Here is how I get started....
    I level the rifle via the lugs, then use a square on top of the parallel to sight a plumb line....then shoot, move, shoot.


    IMAG0370.jpg
     
    Re: Vertical Crosshair to Barrel Bore

    +1 on Straight Shooter's advice
     
    Re: Vertical Crosshair to Barrel Bore

    This is what I use, and it's simple to operate. It's a very powerful magnet that sits on your scope base. Just use it to level your rifle, then rotate your scope to align the vertical crosshair with a hanging string.

    levelmag.jpg


    It's strong enough to lift a Win 94 rifle right off the bench.

    scopelevelmounted.jpg


    You can even shoot with it in place.
     
    Re: Vertical Crosshair to Barrel Bore

    Hellbender ......

    When using an aluminum scope base, I recommend installing one or two 10/32 steel "flat socket cap screw". That works real well.
     
    Re: Vertical Crosshair to Barrel Bore

    Sometimes an hour or two at the range is worth far more than wigits.

    Setup a thermometer tgt on a calm day at 200 yds. Shoot a group, make a 3min shift. Shoot another group, move another 3 minutes. Note the tracking.

    If you start wandering off the centerline/vert axis, rotate the scope accordingly.

    This isn't new. In one form or another this has been done for years with nra HP shooters running irons.

    Good luck.

    C.
     
    Re: Vertical Crosshair to Barrel Bore

    C.Dixon ........

    It's easy to mount a <span style="text-decoration: underline">scope</span> perfectly level before you get to the range, and a good level will help save ammo.

    Whatever method floats your boat ....
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Innovative</div><div class="ubbcode-body">C.Dixon ........

    It's easy to mount a <span style="text-decoration: underline">scope</span> perfectly level before you get to the range, and a good level will help save ammo.

    Whatever method floats your boat .... </div></div>

    perfectly level to what? there is more going on than simply getting the top of the base parallel to the scope reticle.
     
    Re: Vertical Crosshair to Barrel Bore

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Burleyboy</div><div class="ubbcode-body">I use the tool on the bottom of this page. http://www.lyon-inc.com/products/ It works with horizontal split rings and with vertical split rings I run a flat straight piece out leveled across the top of the rail and then set the tool on it. I get the gun level and then line the vertical crosshair up with a string hanging with a weight on the bottom. Seems to get it pretty level.

    Bb </div></div>

    I actually use this tool as well.

    In fact, just ordered some scope levels from Russ...Always impressed with the quality.

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">Sometimes an hour or two at the range is worth far more than wigits.

    Setup a thermometer tgt on a calm day at 200 yds. Shoot a group, make a 3min shift. Shoot another group, move another 3 minutes. Note the tracking.

    If you start wandering off the centerline/vert axis, rotate the scope accordingly.

    This isn't new. In one form or another this has been done for years with nra HP shooters running irons.

    Good luck.

    C. </div></div>

    Ultimately, this is the bottom line, though...Even with mounts/levels etc, nothing is going to outline performance like some well placed rounds on the range, will.
    wink.gif
     
    Re: Vertical Crosshair to Barrel Bore

    If the cross-hairs are canted but the travel is plumb, your dialed come-ups will be on target while your reticle hold overs will be off. Inversely if those crosshairs are leveled your dialed come-ups will be off. To check for this condition level the reticle with a plumb bob then dial a large come-up (or down) then compensate back down with the reticle. If your group shifts your reticle is canted in relation to your dial travel. At that point you need to decide if you are a knob guy or a reticle guy.
     
    Re: Vertical Crosshair to Barrel Bore

    LEVEL means nothing, all other things being equal, you could mount your scope while the rifle is cocked at 30 degrees.

    You bring the scope into a state of parallelism or perpendicularity to the axis of the bore.

    The level aspect comes into play only as a method by which to facilitate the alignment.
     
    Re: Vertical Crosshair to Barrel Bore

    Killer Spade 13 ......

    If your horizontal crosshair is level and your rifle is canted 30 degrees, your rifle would need to always be fired while it's canted at 30 degrees.

    Some of the top High Power shooters actually do this to get into a more ergonomic position. However, most shooters do not, and it's best to first level your rifle - then level your scope parallel to a known vertical or horizontal reference.
     
    Re: Vertical Crosshair to Barrel Bore

    I never said the horizontal was "level".
    What I said is that you can have your rifle tilted "X" degrees and still have the horizontal cross hair PARALLEL to the X axis of the receiver/bore.

    Keeping in mind that the horizontal cross hair is actually being put in a parallel relationship to the X axix of the receiver, not to the barrel. One assumes that the barrel and receiver are in alignment.

    LEVEL comes into play ONLY when fixturing the receiver/rifle in order to facilitate the alignment of the cross hairs to the receiver/barrel assembly.
     
    Re: Vertical Crosshair to Barrel Bore

    I never said the horizontal was "level".
    What I said is that you can have your rifle tilted "X" degrees and still have the horizontal cross hair PARALLEL to the X axis of the receiver/bore.

    Keeping in mind that the horizontal cross hair is actually being put in a parallel relationship to the X axix of the receiver, not to the barrel. One assumes that the barrel and receiver are in alignment.

    Sort of like "flat". An object does not have to be "level" to be "flat".

    With the cross hairs and the receiver/barrel assembly you are merely bringing 2 planes into a parallel condition. IT HAS NOTHING TO DO WITH BEING LEVEL.

    LEVEL comes into play ONLY when fixturing the receiver/rifle in order to facilitate the alignment of the cross hairs to the receiver/barrel assembly.

    The alignment between the scope and receiver/barrel assembly is a MECHANICAL relationship ONLY, not a physical relationship.

    The physical relationship (level) manifests itself only in the fact that a projectile is expelled from the end of the barrel.
     
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