Rifle Scopes The Level Questions Asked

[Deleted member 10043]

Also, I see a lot of people here go to extraordinary means to get either the scope or the reticle level or plumb, respectively. Then they square their body to that level of level not realizing there is up to 5% mechanical tolerance on most scopes built-in. It is really better to level the scope in your shooting stance. Any immaterial error you introduce may improve that tolerance. So, we go to all this trouble getting everything square on the table then go shooting and discover when our spirit level is level and the bottom of the vertical reticle is distorted as well as ourselves we have introduced material cant behind the rifle. So, the whole debate to me is over the top. On hypotherical flat ground we will not introduce material cant without a level. It is not mandatory or a must have.

 

[FromMyColdDeadHand]

What is the use of that little level on the Spuhr mount? You cant (ha, ha) see it from the shooting position. Is it just for setting the rifle up? I put a level on my 22lr trainer and I was surprised how off I was at times and even when the gun was comfortable. I had an adjustable butt plate that I just put on last night before reading the thread.
So your reticle has to be plumb to the world, correct? From there:
If you gun has a fixed butt stop and cheek get the gun as comfortably consistent as possible, even if not 'square' and then mount the scope so that is plumb. IIRC, this is what Tubb recommended in the past for AR platforms?
If you have an adjustable stock, when it is plumb (as in the rail is level) get the gun adjusted to be comfortable.

Found this online: "Bryan Litz confirms Tubb’s observation. Bryan tells us that, as a general rule of thumb (for common cartridges), a 1° cant will produce five (5) inches of lateral displacement at 1000 yards. Thus, if you cant your rifle just 8°, the POI would move 40″ from the center of the target, putting the shot off the edge of a 72″-wide target."

That's a lot of cant.

 

[fastfwd]

What is the use of that little level on the Spuhr mount? You cant (ha, ha) see it from the shooting position. Is it just for setting the rifle up?

It seems that way to me, because Spuhr also provides a little wedge to square the scope to the mount... So I think their expected mounting procedure is:

1. Spuhr mount on the rail, scope loose in the rings.
2. Rotate the rifle until the mount's built-in bubble is centered.
3. Use the wedge to square up the scope.
4. Tighten the rings.

Now the reticle and rifle are both level to gravity on your bench.

To get the reticle level in your shooting position, you do one of two things:

1. If you have a buttplate that rotates, establish your position and then rotate the buttplate until the mount's built-in bubble is centered once again, or
2. while the rifle is still on the bench -- with it and the scope level to gravity -- you affix a bubble level to the scope tube and center its bubble. Now that bubble will directly indicate whether the reticle is level, regardless of the cant of the rifle. So loosen the rings, establish your position, rotate the scope until the scope-mounted bubble is centered once again, then tighten the rings.

 

[Deleted member 10043]

What is the use of that little level on the Spuhr mount? You cant (ha, ha) see it from the shooting position. Is it just for setting the rifle up? I put a level on my 22lr trainer and I was surprised how off I was at times and even when the gun was comfortable. I had an adjustable butt plate that I just put on last night before reading the thread.
So your reticle has to be plumb to the world, correct? From there:
If you gun has a fixed butt stop and cheek get the gun as comfortably consistent as possible, even if not 'square' and then mount the scope so that is plumb. IIRC, this is what Tubb recommended in the past for AR platforms?
If you have an adjustable stock, when it is plumb (as in the rail is level) get the gun adjusted to be comfortable.

Found this online: "Bryan Litz confirms Tubb’s observation. Bryan tells us that, as a general rule of thumb (for common cartridges), a 1° cant will produce five (5) inches of lateral displacement at 1000 yards. Thus, if you cant your rifle just 8°, the POI would move 40″ from the center of the target, putting the shot off the edge of a 72″-wide target."

That's a lot of cant.

That there is the problem. People assume they are level. Litz also spouts we can descern 3 degrees of cant with the human eye. How many degrees of cant will cause a spirit level to be outside the lines? How many degrees of cant is built into the reticle based on manufacturer tolerance specs? You square up your rifle to the scope/reticle get into shooting position only to cant in your comfortable firing position behind the rifle because you are getting a false indicator by your spirit level. All these immaterial introduced cants my be adding up to dry shit or only making it worse. And how the Hell are you going to know you only have 5 degrees cant at 1000 yards when you have several other factors to take into account? How can you guarantee a bubble level is eliminating this factor? You can't. No pun intended. Fuck a bunch of rotating stocks. Just add one more thing to the illusion.

 

[fastfwd]

How many degrees of cant will cause a spirit level to be outside the lines?

I guess it depends on the spirit level. Half a degree is enough to move mine clearly outside the lines.

How many degrees of cant is built into the reticle based on manufacturer tolerance specs?

I don't know, but a quick web search brings up this test from 4 years ago at precisionrifleblog.com, in which 18 high-end tactical scopes were evaluated:

http://precisionrifleblog.com/2014/08/22/tactical-scopes-mechanical-performance-part-2/

One scope had 0.5 degrees of reticle cant, three had 1 degree of reticle cant, and fourteen had no measurable cant. And most of the high-end manufacturers have very good warranties; I imagine that if you had a scope with a degree or more of cant, they'd exchange it.

 

[Deleted member 10043]

High end scopes have low tolerances. More common ones used by us commoners can easily have 3 degrees and no sending it back is going to make a difference. I'm talking reticle cant/level scope. Some people just concentrate on a level scope not thinking the manufacturer are cutting them loose with the Reticle +/- 1.5 degrees. That is why a plumb line is important but I have also just holding the rifle in my shoulder and looking for a left or right distortion at the bottom of the vertical reticle is a good indicator. It should appear straight all the way down.

 

[FromMyColdDeadHand]

Level/plumb the reticle to a vertical line. I don't trust flat bottoms, turret tops.

Take a level and use it vertically to mark vertical line, then turn the level 180 degrees and draw a new line. The degree of difference from parallelism shows how off the level is. That should take out the noise from the level not being calibrated correctly.

FASTFF- your way was how I was thinking of doing it

 

[Bart B.]

The horizontal change in bullet impact for a given cant equals bullet drop at target range times the sine of the cant angle. Vertical change is insignificant for the first few degrees.

 

[Deleted member 10043]

In English please.

 

[Glassaholic]

The horizontal change in bullet impact for a given cant equals bullet drop at target range times the sine of the cant angle. Vertical change is insignificant for the first few degrees.

Ummmmmm.... what??? You math geniuses drive me nuts, but then of course someone has to write the code for ballistics software This reminds me of a quote from a mentor - "if you think you understand Quantum Physics, you haven't been paying attention."

 

[Bart B.]

OK, Culpepper, here's the first part in English.

Do you understand that bullets drop virtually the same amount at target range regardless of where the muzzle axis points? This is for horizontal line of sight +/- 1 degree vertically.

If not, this has to be well understood before going further.

 

[Glassaholic]

OK, Culpepper, here's the first part in English.

Do you understand that bullets drop the same amount at target range regardless of where the muzzle axis points?

If not, this has to be well understood before going further.

Does it? I thought that was the point of incline/decline compensation, that if the axis was up or down your drop will change?

 

[Bart B.]

Ummmmmm.... what??? You math geniuses drive me nuts, but then of course someone has to write the code for ballistics software This reminds me of a quote from a mentor - "if you think you understand Quantum Physics, you haven't been paying attention."

It's simple 7th and 8th grade trigonometry using 4th grade math.

 

[Bart B.]

Does it? I thought that was the point of incline/decline compensation, that if the axis was up or down your drop will change?

Yes, it does. What trig function calculates the drop difference for a cant angle?

Note the line of fire is seldom more than 1 degree above the line of sight in horizontal fire. I edited my post to clarify this.

 

[spife7980]

 

[Deleted member 10043]

Hey, I don't care how it gets there I just need to know if we need a bubble level on flat ground during a string of shots. The OP is wanting know if you use a level on flat ground and if so, why. I gave my answer right off and then continued to troll because people are afraid to answer or follow instructions.

 

[Bart B.]

Hey, I don't care how it gets there I just need to know if we need a bubble level on flat ground during a string of shots.

Yes, you need one if you don't use some other way to keep the cant angle the same for each shot.

 

[Bart B.]

Can a 5 year old understand this to see a 6 degree cant moves impact about 10 inches sideways?

Then use trig to calculate his own ammo's bullet impact shift for a given cant angle?

 

[spife7980]

I get it and was trying to make insert some humor in place of your condescension but hey, you almost caught the joke but you better be a quicker than that.






For everyone else who isnt a haughty math whiz theres already an article on this with some numbers tied to some graphics by frank
https://www.snipershide.com/training-lesson-mechanics-rifle-cant/

 

[Bart B.]

I get it and was trying to make insert some humor in place of your condescension but hey, you almost caught the joke but you better be a quicker than that.

I took your post at face value 'cause I'm not smart enough to think between your words.

But I shoot my stuff precise enough to resolve about 5/8ths inch windage error at 1000 yards with one shot. And simply multiplied the scope offset by 9 to get the shot offset at 1000; no fancy trig math needed.

 

[Deleted member 10043]

Is that the guarantee that came with the rifle?

 

[Bart B.]

Is that the guarantee that came with the rifle?

Yes. Its barrel was 999 yards long.

 

[Glassaholic]

It's simple 7th and 8th grade trigonometry using 4th grade math.

That is assuming that you think 4th grade math is easy

 

[Glassaholic]

Can a 5 year old understand this to see a 6 degree cant moves impact about 10 inches sideways?

View attachment 6960460

Then use trig to calculate his own ammo's bullet impact shift for a given cant angle?

I'm a visual learner so this makes more sense to me... I think.

 

[Glassaholic]

Where did you find that video of me

 

[RTH1800]

But they look so taticool…....
Seriously, I use about everything but the kitchen sink when I set up a rifle/scope. I then fit the rifle within the limitations the system permits. Then, off go the levels and other gadgets.

 

[fastfwd]

Seriously, I use about everything but the kitchen sink when I set up a rifle/scope. I then fit the rifle within the limitations the system permits. Then, off go the levels and other gadgets.

When you say that you set up the scope and then fit the rifle, does "fit the rifle" include ensuring that the scope reticle is level even if the fitted rifle ends up canted left or right? Because this thread has gone all over the place, but I think that was the point that Frank was initially trying to make -- that if you know your reticle is going to be level when you're in your natural shooting position, an external bubble-level is redundant and unnecessary for shooting accurately in a normal environment.

 

[RTH1800]

I set the scope up square to the rifle or as nearly as I can. And that includes trying to figure out exactly what on the rifle I am squaring with. Then I fit the rifle so it sits square in my position, or as nearly as it can.
Likely backwards but I simply don't care to set a rifle/scope up canted if I can help it. David Tubb sets his up for level when in rifle is canted it appears from photos. I am sure this is correct. I am just a crow, coyote and squirrel shooter who does a little range shooting to 1000 yards casually. If I can kill a crow at 500 meters with my .204 or head shoot a squirrel at 100 yards with my 52 I am happy for a week.

 

[fastfwd]

I am just a crow, coyote and squirrel shooter who does a little range shooting to 1000 yards casually. If I can kill a crow at 500 meters with my .204 or head shoot a squirrel at 100 yards with my 52 I am happy for a week.

You mean, you get more enjoyment from shooting your rifle than from clamping it in a vise and dicking around with levels and torque wrenches for hours at a time? Weird.

 

[RTH1800]