Scope Levels- Why?

[Mram10us]

This is for a canted reticle, while not commenting on bore/optical axis relationship.

This one mentions it but I haven't read it all.

Cant Errors Explained - RifleScopeLevel

(also see “Varmint Hunter” July 1999 magazine article)

www.riflescopelevel.com

 

[LRNut]

This one mentions it but I haven't read it all.

Cant Errors Explained - RifleScopeLevel

(also see “Varmint Hunter” July 1999 magazine article)

www.riflescopelevel.com

That story looks very familiar, but I will admit the vertical drops were a lot more than I expected. A ballistician took me to task on that, and I think he was right. Still a bit puzzled.

 

[Rich Coyle]

How were they not any good? I've bought some amazon $5 specials and they worked

Everyone of the screws eventually pulled through the "clamp". The material is not tough enough.

 

[Mram10us]

Everyone of the screws eventually pulled through the "clamp". The material is not tough enough.

Did you use Ftlbs when torquing

 

[Rich Coyle]

Did you use Ftlbs when torquing

No.

 

[JustMe2]

Your barrel has no clue or preference at what angle it is shot at. Reticle is the only thing that needs to be level. You can shoot your stock at a 45 degree angle if the reticle is level. Just think about it for a second.

Wrong, wrong, wrong. You need to rethink this for about a minute instead of a second. If your scope is not directly aligned over your barrel, you will shoot to the same side of your target as your cant when you dial for long ranges (ie. right cant = miss right, left cant = miss left). The scope ring height results in a triangle shape between your barrel and the scope, so you need to apply your trigonometry to calculate the results. If the scope was looking down the center of the barrel, you would be correct, but it isn't, it is 1.5 inches above your barrel. So, when you cant, the center of the scope moves 1.5 inches to the side resulting in a triangle.

 

[tribb]

Don't get wrong; I agree. But I would also

Antelope: there are now two discussions going on; one is for cant due to not having a level, and the other is for the question of "does the rifle need to be level the same time the scope is level?" I concluded the drawing he created was illustrating the later. You are illustrating the former.

Yep

 

[mwkelso]

@LRNut
If the rifle is canted but the reticle is plumb, I would think that could be accounted for. I know inside the shooter app there is an input for optics offset.
But if the center axis of the reticle/scope and barrel are plumb in their alignment, would the effect from cant still calculate the same? Or would it likely be amplified in both windage and elevation affects?

 

[mwkelso]

Thanks for the very productive input on this one guys! I'm picking up more information that I wouldn't have put to thought without the feedback on this thread.

 

[Pro2A]

I'm currently reading Ryan Cleckner's "Long Range Shooting Handbook" and he explained the reason he doesn't use scope levels is because he's never seen one accurate enough to make a critical difference. When every degree matters at long range that bubble level just isn't going to give you 100% accuracy. If your eye doesn't naturally pick up plumb / level easily than perhaps they could help to some degree, I lived a former life as a frame carpenter so my eye naturally sees anything out of level ... drives me nuts! lol

I'm also not saying my eye is better than a bubble level, but like Ryan I feel they are at least comparable. Now if we get into digital levels that are gaining traction in the trades then we may have something to talk about given the higher levels (pun intended) of accuracy they can provide.

Just read Ryan's book also. Interesting entry info. Did your book's binding fall apart like mine??? Looking forward to his sequel due out this year. Just because available bubble levels are not precise doesn't mean cant should be ignored as big source of inaccuracy.....all increments are additive yielding cumulative misses. Consistency is King. Frank Galli, when quizzed at 2018 Precision Rifle Expo at Arena Training Facility in SW GA, said he "didn't need one".....and couldn't/declined to offer any advice for we mere mortal trigger pullers who haven't been taxpayer funded to send a bazillion rounds down range. As a mere mortal trigger puller, I find very useful the SendIt! digital level (~$230 at Brownells.com) attaches to picatinny rail. Choose from any of 5 sensitivities down to 0.1deg; 5 LEDs....2 Red/2 blue LEDs = cant; center green = Send It!. (Note: 0.1deg cant LEDs can drive you crazy worse than the wandering reticle.) Mount horizontal or vertical. High peripheral visibility without lifting from optic....no need to "read" bubble. Works for me. Also, I have several Sig Tango6 5-30x56 with their Level-Plex digital level. Selectable precision, I recall between 1deg to o.1deg. Really nice as the level indicator is in the optic....no lifting to "read" a bubble. Machinist bubble levels (ie. Starrett...) can be very precise....gettin' really, really old...forget the specs, but no mount for rifle available anyway. Haven't machined mount; still difficult to read peripherally without lifting. Checked against machinist level or indicated on mill, most shooting bubble (Vortex, NF, Accuracy 1st,...) levels are in the 1-3deg accuracy range. Seems bubble benefit is largely in keeping shooter aware of cant issue....first step to resolving an issue is being aware of issue.......and maybe a little Tacticool.....play with your opponent's mind. Bryan Litz, Applied Ballistics, in Chapter 8: Leveling Your Sights in his book Accuracy and Precision For Long Range Shooting - A Practical Guide For Riflemen, relates studies show that without an accurate reference, average individuals are hard pressed to resolve cant +/- 3deg with unaided eye. That is big impact at long range.....500 - 1000yds out. Litz's Fig 8.2 page 95 plots horizontal and vertical error of 3deg cant for .243 and .308 as roughly 3-4.5" horizontal/0.1" vertical @ 500yds; 1000yds = 16-25" H/0.4-0.6" V ; 1500yds = 41-66" H/ 1-7" V. Worth addressing??? Really major contribution to misses. Most error is obviously horizontal which also compounds the reading wind issues. Cant typically gets mis-read as wind errors. Many field visual references....telephone poles, fence posts, trees, etc can be sneaky vertical illusion. Just an old guy's ponderings.

 

[Pro2A]

What about internal digital scope levels (vx6 etc)

Didn't realize Leupold had internal digital levels. I have several Sig Tango6 5-30x56 with their Level-Plex digital level. Selectable precision, I recall between 1deg to o.1deg. Really nice as the level indicator is in the optic....no lifting to "read" a bubble.

 

[An Idahoan]

The attached six pages of illustrations attempt to help anyone who is interested in seeing what is going on with the following configurations:
Scenario 1: Optical axis and bore on same plumb-lines; reticle plumb (page 1)
Scenario 2: Optical axis and bore on different plumb lines; reticle not plumb (page 2)
Scenario 3a: Optical axis and bore on different plumb-lines; reticle plumb (page 3)*
Scenario 3b: Optical axis and bore on different plumb-lines; reticle plumb (page 4)*
Scenario 3b: Cont'd analysis (page 5)
Scenario 3b: Cont'd analysis (page 6) [although this illustration could apply to Scenario 3a as well]
* the difference between scenarios 3a and 3b are only the horizontal zero

My hope is that this will help people see that if horizontal zero issues are understood and properly accounted for when zeroing the rifle, someone can shoot a rifle with the optical axis and bore "canted" as long as the reticle consistently plumb (and therefore the need for a level). The advantages for adopting such a setup are:
1) More comfortable and natural shooter interface with the rifle (not everyone loves a perfectly plumb rifle butt)
2) Simplifies the scope mounting "problem" therefore saving time and potentially money wasted on devices aimed at solving a problem that doesn't exist.

Standing by for questions and counter-fire!

 

[J E Custom]

To Me It is very simple, If you make everything true and level. you wont have to compensate for it.
Start right and end right. I know and have shot against some shooters that cant their rifles. I also often wondered how good they would be if they didn't cant the rifle. obviously, they figured out how to get around the problem and are ok with having to constantly adjust for this condition and
powered through it.

We can train ourselves to do almost anything. but if we train our selves to compensate for something that is not correct, in my mind it is harder and is never correct.

If you build a house, do you level the floor or the walls. It wont hurt the weather proofing but everything will have to be adjusted to compensate to keep your mind straight and level. when building a rifle not clocking a fluted barrel or a muzzle brake will not hurt the performance in most cases, but it can in some.

So their is really nothing wrong with canting a rifle. "BUT" there is nothing right about it to most, and with out pursuit of accuracy for longer distances why handicap your self and add other variables to an already complicated process.

J E CUSTOM

 

[An Idahoan]

Ok, I just did the math using trig and similar triangles...a 45 degree cant on the rifle, assuming a scope height of 1.75" and a 200 yard zero would result in horizontal error of 3.7" at 800 yards - no thanks. A 10 degree rifle cant (with the scope reticle leveled) would result in a one inch error at 800 and a 1.5" error at 1200. Not huge, but if you are trying to hit a ten inch plate at 800 and only shoot 4 inch groups, you are giving up 1/3 of your allowable wind call error 50% of the time (the other 50% you increased it by 1/3). And in real life, after practicing, you might think you are seeing spin drift and learn to compensate.

So I will concede not as dramatic as I thought.

Again, this is for the reticle level but the rifle canted.

I independently arrived at the exact same results as LRNut after I couldn't figure out the .xlsx he emailed me. If LRNut is saying there is zero vertical error to this setup (reticle level but the rifle canted) then we're on the same page at this point. Further, there is a method whereby you can zero your rifle differently and mitigate this horizontal error (see my post above, Scenario 3a would be my recommendation).