Help me understand optically centering a scope

[Pellgunfun]

The mirror method will simply "ball park" the scope in my opinion:-)  I use both methods.  The mirror method to get me close, then I move in for the kill using the V-block method. 

Someone here asked about this method of scope mounting on air guns verses regular powder burning firearms.  Yes, it is used on powder burning rifles too.  I think having the scope centered and perfectly aligned with the rifle bore is even more important on powder burning rifles, than it is on air guns.
Sadly, mass produced factory rifles often have errors with the scope mounts NOT being perfectly aligned with the bore.  I've seen these errors on many mass produced rifles.  Doesn't really matter what the brand name is.  It's a shame when most air rifles today are built to better standards than many mass produced firearms.

Many hunters don't ever bother trying to "square" things up.  They just slap on a scope, zero at 25 yards and go hunting.  Heck, many hunters can't hit anything beyond 150 yards, and seldom ever try.  They never realize the true benefit of having everything "squared" up, and just assume that everything is square, when in fact it isn't.

[rsterne]

Angles are angles, if you are studying engineering you should know that.... as I said, I have one scope (actually a Bushnell) where the end of the bell is 0.020" out of square with the side of the tube on a 2" diameter.... That is (0.020" / 2.00") x 100 yards = 1 yard or 36", so if you used the mirror method that would be the error in angle relative to the scope centerline.... I shouldn't have multiplied by two, however, that was incorrect.... Using a mirror to try and center THAT scope was useless.... I have other scopes where the bell is out of square between 0.003"-0.007", but on about 2/3rds of my scopes I can't measure any error, so using a mirror on those would work fine....

I apologize if you feel my answer is condescending, but all I'm trying to do is point out a problem with a method that is often quoted and does NOT work unless the scope objective housing (which is what you are putting the mirror against) is perfectly square with the centerline.... If you don't think it matters, center your scope using a mirror and then slide a piece of paper under one edge of the bell and I guarantee you will again see two reticles.... I discovered this quite by accident, published it as a warning here on the GTA about a year ago, and I have never seen anywhere else on the Internet it is mentioned.... Sometimes commonly accepted things have built in errors people just haven't noticed.... One of the benefits of Forums such as the GTA is the ability to pass on experiences that can dispel such (potential) myths....

Bob

[BobbyHumphrey]

   Apology accepted. You have bedazzled me yet again with your awesome AG jargon.

    I still think your numbers are wrong but I'm not smart enough to prove it so I'll let it go.
 
     A friend whom I was talking to about the fantastic world of airgunning (he wanted to know why I chose engineering) asked me what gun I would have if only I could have one in all the world. I just finished showing him pictures of the best ones I could find by keywording top airguns,most expensive airguns, etc.,and it hit me. If I could have any gun it would be the pumper you made with the lothar wather barrel,that beautiful stock, and amazing power. That thread was so interesting. Actually fascinating. The ones you have discussing qb"s (as well as nervoustrigger) are among my favorite as I have a jc higgins waiting to be converted to hpa.I literally have read everything you have written here and what I could find elsewhere.

    This is my second week of my freshman year so I dont know jack  yet. I've learned far more here than at school. Let it be known that my desire to make the things you make,to be more like you, is what led me to choose engineering. So thanks, and thanks gta.

[f4milytime]

   I've personally found the v-block method to be a pain.  I used to do that. The block method may theoretically get you more percise but that little bit deosn't matter at all with your set-up.

   And short of spending maybe 50 % of what the N. V. costs on adjustable mounts , you could bend the barrel. I've found adjustable mounts to have there own problems as well.

    1.  Something else that can go wrong ( esp. with springers )

     2. Cost. You have an N. V.
     
     3. Scope height. I like mine close to the barrel. Thats just me though.

     4. Avaliability. You can literally go out to your garage ( or back yard tree ) and bend it.

     5. I have not found one good reason not to , at least on an unshrouded springer.

    And  as mentioned above you could shim the mount, or scope rings I should say. Although this can be done for slight vertical adjustment , much can go wrong with this method (like bent scope tube due to poor seating of the scope) , and you can find tuners who recomend against it. Again, esp on springers. Adjusting the windage with the scope rail? What a PITA that would be. On a one piece mount maybe but why do it on a N.V. when you have an easier, more sound solution?

    I mean you could take it to a machine shop and have the parts re-made in perfect alignment but why not tell people how effective and easy  and free it is to use the barrel bending tutorial found on this site? I did, and my 70$ adjustable mount is now on the shelf. The next 2 times I did it I used the the tree fork method to bend that a gentelmen on here said he used.  Results . Thats what I got.

    I sense sarcasm in your post f4milytime. You will find if you research that many top manufactures and tuners bend barrels. I'm no expert , so all I can do is seek expert advise. I've read every post by rsterne , my  A G exemplar. So there's that....




I'm talking about the picture of the pistol you posted.

[Tater]

Noob question here, but how much of this thread would apply to a red dot? Would you see two dots in mirror if it not centered?
 I have no idea what the internals in them looks like so thus the question.

[rdhj]

ok, so if i have this straight...one should optically center their scope as best they can, then mount it to the gun...go to the range and then zero it in....it should not take too many clicks to get it zeroed unless there is some kind of major issue such as barrel droop or misalignment somewhere....  to get the most accuracy you would want to leave the scope optically centered and use an adjustable mount on any gun to do you zeroing.....and i thought it was just as easy as buying a higher quality scope and sighting it in  LOL

[Bullit]

You're on the right track now rdhj.  Don't know what you're shooting, but start at the 10yd mark, just to see what she does.   Don't start cranking on her yet...just use your Mildots for corrections.  It may be waay low or high, but... Then move out to 15 yards, and see what she does.  The 20 yard mark is a good place to start making turret adjustments to zero the scope.   You can fine tune the zero point later,,,when you know your actual fps and pellet selection. 
G'Luck to Ya

[condor22]

ok, so if i have this straight...one should optically center their scope as best they can, then mount it to the gun...go to the range and then zero it in....it should not take too many clicks to get it zeroed unless there is some kind of major issue such as barrel droop or misalignment somewhere....  to get the most accuracy you would want to leave the scope optically centered and use an adjustable mount on any gun to do you zeroing.....and i thought it was just as easy as buying a higher quality scope and sighting it in  LOL

 I still look at my rifle scopes and wonder why they have elevation and windage adjustments because they always move the reticle off of optical center, with adjustable scope rings you really don't have any need for 'em ever!  Maybe the manufacturers are reading and will decide to produce a scope for the optical centering crowd. 'Purely Rhetorical' 

BTW No one mentioned  how to proper verify optical center after using the two methods posted ? Maybe I missed, didn't read the whole thread.  Once you have optically centered the scope uninstalled, install the scope into the rings loosely (somewhat finger tight, but loose enough to rotate). Now carefully rotate the scope without banging the turrets against the receiver. Don't be surprised if optical center has moved, personally I'd use the mounted optical center over the unmounted optical center. U.S. Optics's use to have a video demonstating this method but I can't find it for a link. I'm still searching.

 Here we go: If I ever did optically center a rifle scope, this would be the only method? 
t

[nervoustrigger]

Not sure if you realize it yet, but you are dancing around an alternative to the V-block.  If you have a good way to hold your rifle steady (e.g. Gun vise), place the scope in the rings but leave them loose enough that the scope can spin freely. 

Hello improvised v-block.

Just take care not to scuff up the scope tube as you rotate.  Line the inside of the rings with masking tape temporarily to prevent that from happening.

Now you can go in reverse and use a V-block to verify your results (just kidding...no reason to do that unless it just helps you sleep better at night).

[condor22]

Not sure if you realize it yet, but you are dancing around an alternative to the V-block.  If you have a good way to hold your rifle steady (e.g. Gun vise), place the scope in the rings but leave them loose enough that the scope can spin freely. 

Hello improvised v-block.

Just take care not to scuff up the scope tube as you rotate.  Line the inside of the rings with masking tape temporarily to prevent that from happening.

Now you can go in reverse and use a V-block to verify your results (just kidding...no reason to do that unless it just helps you sleep better at night).

 I totally don't see any similarity? You may want to call a mounted scope ring a C block, V block it is not. The mounted scope rings are rigid and cannot move  any way what so ever.  Nothing rigid or permanent about V blocks. Can't use V blocks on my Airgun, I prefer scope alignment on my Air gun, not off somewhere on a table. 

[nervoustrigger]

What I mean is that either method serves as a fixture to optically center a scope. 

You said to not be surprised if the scopes optical center changes when you put it into the scope rings.  Why would it change?  Optical center is a property of the scope; it has nothing to do with whether or how it is mounted.  The only reason it may have some appearance of having changed is if the mount distorts the scope tube in some way.

There is no reason to do both and neither is inherently superior to the other.

[rsterne]

I don't see how you can rotate a scope in the rings all the way around to check the optical centering of the reticle anyway.... unless those are VERY tall rings.... All of my scopes the turrets would hit the receiver....

Bob

[nervoustrigger]

Haha, good point Bob!  That would have become apparent pretty quickly if one were to try it.  When condor brought it up, it seemed logical that rotating the scope in the mount would yield the same results as a V-block.  You know, except for the whole it's not possible thing 

[K_sqrd]

I found it interesting to read the instruction manuals for a couple scopes I have / had from different manufactures re: optically centering.
For example, Vortex recommends the "Count clicks & divide by 2" method for both their Crossfire II and Diamondback scopes.
Bushnell says to use the "Rotate the scope in a V block" method for both older and newer Trophy scopes while
instructions for an older RWS 450 never addressed the issue. I've used all three methods at different times on various
scopes and found that all of them got me close enough to optical center "for all practical purposes". You engineers should
recognize that last phrase. LOL!

As to the mirror method, I found that using it on a Vortex Diamondback gave me two different optical centers, both of which differed
from the count clicks method per Vortex. One Optical Center was obtained with the front plastic ring installed on the bell and a
different OC with the ring removed and the mirror against the metal bell housing. I essentially had three different optical centers,
all of which were within about 5 clicks of each other. It just goes to show that things are not truly square and accurately built.
On the other hand, a couple of Crossfire II's were centered with the count clicks method and checked with the mirror. It turned out that the
two methods were spot on in agreement. So you never know what you will get and it's nice to have alternative methods.

[nervoustrigger]

I've used all three methods at different times on various
scopes and found that all of them got me close enough to optical center "for all practical purposes". You engineers should
recognize that last phrase. LOL! 

Don't call Bob an engineer.  He doesn't like that very much, haha! 

Reminds me of a quote, paraphrased:
"Things should be done as well as possible...but no better."

I'm in agreement with you that good enough is, well, good enough.  Bob was just trying to emphasize that even the tiniest bit of "unperpendicularity" between the scope tube and the objective bell translates into a surprising amount of error when using the mirror method.  In manufacturing jargon, it's what's referred to as an uncontrolled parameter.  The manufacturer has no particular reason to strive for the precision necessary to achieve this perpendicularity; it adds cost for a feature that >95% of the customer base will have no use for.  And what I was trying to say is that in my opinion, there's just no good reason to leave it to chance when something as simple as a cardboard box or a wooden block can be used. 

[condor22]

What I mean is that either method serves as a fixture to optically center a scope. 

You said to not be surprised if the scopes optical center changes when you put it into the scope rings.  Why would it change?  Optical center is a property of the scope; it has nothing to do with whether or how it is mounted.  The only reason it may have some appearance of having changed is if the mount distorts the scope tube in some way.

There is no reason to do both and neither is inherently superior to the other.

I fail to see your logic, Optical center should be a property of better Accuracy, if it's not......then it's just a complete waste of time.   I see your point, it really doesn't matter where you align your scope, just makes better sense to me aligning it where I use it.   

[condor22]

I don't see how you can rotate a scope in the rings all the way around to check the optical centering of the reticle anyway.... unless those are VERY tall rings.... All of my scopes the turrets would hit the receiver....

Bob

Why would it be necessary to rotate the scope 360 degrees?  Did you miss where I stated "Don't let the turrets bang against the receiver".  You could lay a rag under the scope, to keep from carelessly dinging the scope.

Thanks for your response.  I'll followup after talking to U.S.Optic's cs or ts.

[rsterne]

The more you can rotate the scope, the closer you can get to center.... You are correct that rotating the scope 90ish degrees in the rings can probably get you close enough, as shown in the video.... Realistically, close is all you need, as finding the "mechanical center" which is what all of the methods described in this thread do is not necessarily the perfect "optical center" anyway because the objective lense might not be mounted square to the tube and the bell itself could be off center relative to the tube.... neither are likely, but theoretically possible....

Bob

[condor22]

The more you can rotate the scope, the closer you can get to center.... You are correct that rotating the scope 90ish degrees in the rings can probably get you close enough, as shown in the video.... Realistically, close is all you need, as finding the "mechanical center" which is what all of the methods described in this thread do is not necessarily the perfect "optical center" anyway because the objective lense might not be mounted square to the tube and the bell itself could be off center relative to the tube.... neither are likely, but theoretically possible....

Bob

+1 Thanks, it's just an accuracy thing*

Sam

[rdhj]

Just attempted to center my UTG SWAt 3-12 X44 and not getting to far...Using a grid printed on a piece of paper at 7 yards down the hallway and the AR15 in the caldwell with the top ring caps off (rings have some tape like material for traction on the inside).....did the mirror method first to get me close.......just did the elevation first and had to move the elevation down alot...put it back against the mirror for a look and it looks like the entire lens is up high in the tubes...does that sound right??

now with the windage   it moves both to the left and to the right....how do I know which way I should turn the windage turret to adjust?