scope height above receiver

Status
Not open for further replies.
The scope should be mounted so that it is naturally in line with your eye when the rifle is shouldered. Generally speaking a lower mounted scope is easier to get behind, but stock design also plays a factor. If you have to un naturally hold your face off the stock or lower your face into the stock it can affect how well YOU shoot the rifle. Not the mechanical accuracy of the rifle.

On a hunting rifle lower mounted scopes mean the bullet is closer to the line of sight at close to moderate ranges which can make it easier to hit game at ranges between 50-150 yards. Since ANY sight is mounted above the bore the barrel will always be pointed slightly up at the muzzle in order for the bullet to rise up to your aiming point. The farther the sight above the bore, the more the bullet has to travel up to align with your sight picture.

Mounting the scope higher places it farther above the bore and increases the angle between the two. This means that the bullet will be farther above your line of sight at 50-150 yards which could result in shooting over a small target at closer ranges. At long ranges though this is an advantage.
 
jmr40 said:
The scope should be mounted so that it is naturally in line with your eye when the rifle is shouldered. Generally speaking a lower mounted scope is easier to get behind, but stock design also plays a factor. If you have to un naturally hold your face off the stock or lower your face into the stock it can affect how well YOU shoot the rifle. Not the mechanical accuracy of the rifle.

On a hunting rifle lower mounted scopes mean the bullet is closer to the line of sight at close to moderate ranges which can make it easier to hit game at ranges between 50-150 yards. Since ANY sight is mounted above the bore the barrel will always be pointed slightly up at the muzzle in order for the bullet to rise up to your aiming point. The farther the sight above the bore, the more the bullet has to travel up to align with your sight picture.

Mounting the scope higher places it farther above the bore and increases the angle between the two. This means that the bullet will be farther above your line of sight at 50-150 yards which could result in shooting over a small target at closer ranges. At long ranges though this is an advantage.
Click to expand...

Exactly. I'm kind of disappointed in you for not attempting to make this more complicated than it actually is.
 
"Mounting the scope higher places it farther above the bore and increases the angle between the two. This means that the bullet will be farther above your line of sight at 50-150 yards which could result in shooting over a small target at closer ranges."

No, that's backwards. Easy to check with a ballistics calculator. Figure it with a regular hunting zero, 200 or 250 yards.
 
Would this work?

sin cant, or sin 1 degree = .017, highest point of trajectory = 60 inches, then .017 X 60 = 1.02 inches offset towards tilt direction when cant is 1 degree, then impact would be lower also

at long ranges where the highest point of trajectory might be 3 times more or 180 inches (15 feet) the offset would be like at 1 degree 3.06 inches, with a cant of 5 degrees (sin 5 degrees = .087) the offset would be 15.66 inches. Impact point would be lower also.

since the bore axis would not coincide with the line of sight any cant effect would direct the bullet in the direction of the cant angle and the maximum height of trajectory would be offset and impact low.

I would guess that a 20 MOA base would increase cant effect because it would increase the angle between line of sight and bore axis - the bullet, being affected by gravity starts falling upon exiting the barrel and assumes its trajectory path.

My views on all this are to use a stock having a high comb, a scope with a 30 mm tube allowing maximum adjustments, and level everything using a spirit level on the rifle and a plumb bob lined up with the vertical cross hair. I use a rope with one of my small steel targets hanging from the 2X4 support holding up the target backer at 100 yards; I then line up my vertical cross hair with the rope then adjust my scope reticle. Hopefully, everything in the reticle is at 90 degrees - should be with an etched reticle.

Despite having 2 working eyes looking at a spirit level and reticle and thinking about what to do next is a distraction to what might be happening elsewhere. I would like to have a scope with a level embedded in the reticle and if I had to design one I would attach a shallow U shaped tube, curve down, having an index mark in the exact lower middle, on the bottom of my etched glass lens reticle, the tube would contain a drop of mercury and when the drop of Hg was resting on top of the index mark I would be ready to go. The Hg tube would be huge in comparison with other reticle features and might not focus real good being not in the same focal plane as the rest of the reticle.

On occasion when I shoot snakes up close I crank my scope down to the lowest power and aim over them.
 
Last edited:
Lucubration, no I idea what it meant but just KNEW I liked it. Looked it up: laborious or intensive study; also : the product of such study —usually used in plural.

Howard, you are the man.
 
Of course, bullet will also drop more as the rifle's canted. It can be calculated using the cosine of the angle.

A 1 degree cant has a cosine of 0.9998. That times a 350 inch bullet drop atd 1000 yards equals 349.9467 inches. Subtract that from 350 to get the drop below horizontal; .05331 inch.

As the high point in trajectories is about 60% of target range, it'll be that much of the horizontal drift at target range for a given amount of cant. About the same lower than high point, too.
 
lucubration is hardly a usual word - not my shabby paper-backed Oxford Dictionary or the M-S Word Thesaurus but Merriam-Webster had it. I am surprised that the spell checker in this forum did not go red.

My thoughts are that numerous anti cant devices may be had for between $35 to $150 so there just has to be more than indifference to the cant subject or various manufacturers would quit making them and the market would dry up. Cant is a consideration for long range shooting often at improvised positions and for less than $50 you can buy a bubble level but knowing how it works what it will fix is of use.

One pic of the display of several aperture front sights having bubble levels showed what a 1 degree cant would look like in a bubble level but I would be indifferent (meh?) to some item like that for long range varmint shooting using big scope sights that are mounted high above the receiver and allowed by fish and game regulations. Did I miss seeing a bubble level attached to a scope?
 
cdb1 said:
I plan on getting a rifle chambered in .308 Norma Magnum and finding a good load with 200 grain bullets. I'd like to get a Schultz and Larsen.
Click to expand...
That's a virtual twin to my 30-338 Win Mag. I've worn out 3.5 barrels and 65 grains of IMR4350 under Sierra 200's shot well under MOA through 1000 yards.
 
Back to the op and scope height on a stock Rem 700 rifle for varmint use.. I don't know much about levels and all this other stuff. I have been using varmint rifles since 1975. Four of them. All with heavy barrels. A Sako .222, Rem 700 .243, custom Mauser single shot 22-250, and a Cooper .204. Using them in the field, i.e. from a scabbard hanging on a horse, quad, Honda trail 90, or laying on the back seat of the truck, and almost always firing them with some kind of rest, the lower the scope the less there is to get knocked around. I also use scopes with smaller front bells in order to keep them low. I have one 30 mm scope and it does seem to have a little more brightness than a 1 inch scope of equal front bell size.
These rifles got used for what they were. I do understand levels, cant, and the rest and it is very important when a truly accomplished shooter babies his sophisticated expensive rifle to the range, gently shoots it and cautiously transports it home.
When the coyote pops up there isn't time for all that.
Most off the shelf rifles produced here without iron sights have a stock cut that will be fine for normal humans that choose low, medium, or high mounts.
It's the long range competitive smallest group size shooters that really need to watch that stuff.
 
win71 said:
Back to the op and scope height on a stock Rem 700 rifle for varmint use.. I don't know much about levels and all this other stuff. I have been using varmint rifles since 1975. Four of them. All with heavy barrels. A Sako .222, Rem 700 .243, custom Mauser single shot 22-250, and a Cooper .204. Using them in the field, i.e. from a scabbard hanging on a horse, quad, Honda trail 90, or laying on the back seat of the truck, and almost always firing them with some kind of rest, the lower the scope the less there is to get knocked around. I also use scopes with smaller front bells in order to keep them low. I have one 30 mm scope and it does seem to have a little more brightness than a 1 inch scope of equal front bell size.
These rifles got used for what they were. I do understand levels, cant, and the rest and it is very important when a truly accomplished shooter babies his sophisticated expensive rifle to the range, gently shoots it and cautiously transports it home.
When the coyote pops up there isn't time for all that.
Most off the shelf rifles produced here without iron sights have a stock cut that will be fine for normal humans that choose low, medium, or high mounts.
It's the long range competitive smallest group size shooters that really need to watch that stuff.
Click to expand...


I agree with everything but the 30mm scope being brighter because it has a larger diameter tube than a 1" scope. I'd be willing to bet it's the glass that makes the scope brighter.
 
Oh boy cdb1, you may be really right. The 30 mm is a Zeiss.
Pretty good insight.
I also have a 15 year old Leica 20-60 spotting scope. Makes almost everything at the range look blurry. It is the glass.
 
On this subject you can certainly get technical. On the other hand if the height (what ever that might be ) is comfortable and everything is clear and the sight in process goes well..........
 
win71 said:
I have one 30 mm scope and it does seem to have a little more brightness than a 1 inch scope of equal front bell size.
Click to expand...
The size of the front lens determines how much light gets into it then funneled into the main tube and into its lenses. All 30mm lens captures the same amount of light. That main tube diameter doesn't matter; its just a pipe light goes through. The lens glass and coatings determine how much light entering it gets through it as well as the other lenses and into your eye.
 
Last edited:
Scopes - should 1 real good scope that can be switched from rifle for a certain need be better than 3-4 scopes of lesser quality that on occasion present frustrations? Big objectives, high quality glass/coatings, lots of brightness, big size, high mounting and precise adjustments = $$$

On the scope height business - I played around with the Hornady 4 Degree of Freedom ballistic on line program, my reasoning was that this software was derived from Doppler radar under controlled conditions and should have a high degree of validity. As expected there are many variables that are accepted as input data. I was only concerned about scope height, velocity, bullet, range, and both drop and maximum height above line of sight. I ran data without any effects of wind, elevation, and temperature. I selected Hornady's 75 .224 ELD M @ 3150 fps (.22-250 with a variety of 4350 powders) the other bullet was Hornady's 178 .308 hpbt @ 2650 (seems good for a .308W).

What turned up:

.308 with 178 @ 2650
Drop @ 1000, 50 yard zero -374 inches, scope height 1.5 inches
High point trajectory, 1000 yard zero 130 inches, scope height 1.5 inches

.22-250 with 75 @ 3150

Drop @ 1000, 50 yard zero - 274 inches, scope height 1.5 inches
Drop @ 1000, 50 yard zero - 255 inches, scope height 2.5 inches
High point trajectory, 1000 yard zero 100 inches, scope height 1.5 inches

Cant errors

Looking at stuff on the internet I saw a variety 3.5 inches @ 1000 with 1 degree, 5 inches @ 1000 with 1 degree, Bart B calculation using the sine of 1 degree * drop would give 6.52 inches with 1 degree with a -374 drop.

I looked at:

//scopelevel.com/Default.asp

and

//www.riflescopelevel.com/cant_errors.html

The first link gets into calculating cant effects using max height trajectories and provides a diagram to do this - the fact that the bullet is still in flight and needs to complete the end 40 % of its path the 1000 yard target is not addressed.

The second link addresses the path beyond the high point trajectory but does not provide a numerical solution or estimate. However, I real good diagram is presented showing the "error triangle"

My solution was to use the error triangle with the sine of the cant angle * height of max trajectory @ 60% = cant error at max height, then determine the slope using the cant error back to 0 range, then having the slope project the cant angle forward to 1000 yards to determine cant error @1000. As expected the slope being rise (y axis) / run (x axis) was huge as the 600 yard rise was compared to the inches wide run.

I used an Excel spread sheet to do this.

I got 3.78 inches using projected max trajectory height vs 6.52 using drop with the .308 -- 1 degree cant

I got 2.91 inches using projected max trajectory height vs 4.78 using drop with the .22-.250 -- 1 degree cant

My thinking is that calculating cant using the actual trajectory at a certain range is more like an actual situation provided an estimate of the remainder of the bullets path beyond the high point of the trajectory is done.

The folks at Hornady did not have a way to calculate cant but suggested that is followed trajectory (MOA) and that a level would be a good idea.
 
Last edited:
3 inches of cant error at 1000 with a 1 degree of cant is not much even less at usual varmint ranges of 200 -400 (for me)

Other factors like wind and even "wind drift" as mentioned in the Hornady program could be more important. My usual varmint rifles are a .20 Practical, 40 VMax @3700; .204 R, 40 VMax @ 3750; .22-.250 75 Amax @ 3150; .243 W , 87 VMax @ 3200; and 6mm AI 95 Berger VLD @ 3300. Cant is usually of no concern out on the rodent fields - high velocity, flat trajectory, mid ranges <600, but what if I wanted to reach out to the end of the section or about 880 yards should I be in the middle of the section.

IMG_0007.JPG

The lighter brown area just below the horizon, right side, about 2:00 from road line, is at the section border about 880 yards out. Just at the edge of the light brown area there is a fence that runs left to intersect with a gate across the road. Note that there are no horizontal or vertical features to line a reticle up with - everything is slanted - where is "up" ?

I have a level attached to my rifle

IMG_0996.JPG

IMG_0994.JPG

The level is plastic "ScopeLevel" brand and cost about $30. I can see it easily through my shooting eye just by looking above the reticle. Note that the level shown on the rifle has been turned around to enable it to be folded down more.

Removing that 3 inches or so cant error might enable a hit on a small rodent out there. I like to wait until they are horizontal presenting the widest target - most misses are due to left or right errors.

Multiples of section widths like 110, 220, 440, 880 seem to work out well with 660 yards for prelim guestimates.
 
Last edited:
Regarding:
RugerBassMan said:
I looked at:

//scopelevel.com/Default.asp

and

//www.riflescopelevel.com/cant_errors.html
Click to expand...

How many readers can spot the big error regarding bullet drop (Figure 3) in the second link shown?

Bullet drop at target range is calculated from where the line of fire intersects the vertical plane of the target above the line of sight. Not from the high point in the bullet trajectory above the line of sight that's about 60% of target range.

A bullet zeroed at 600 yards with a 100 inch drop will leave the line of fire (LOF) pointed 100 inches above the line of sight (LOS) on the target. Cant the rifle 1 degree, then 5 degrees; here’s what happens:

1 degree cant: drop (100) times sine of 1 degree (.01745) equals 1.745 inch movement to the right for the LOF. The bullet drops 100 inches straight down from that point. It goes 1.745 inch to the right of LOS. Drop (100) times cosine of 1 degree (.99985) equals 99.985, subtract that from the drop (100) and get the bullet drop from the horizontal; .015 inch. That’s how far below the 1 degree canted LOF is from where it was without cant.

5 degree cant: drop (100) times sine of 5 degrees (.08715) equals 8.716 inch movement to the right for the LOF. The bullet drops 100 inches straight down from that point. It goes 8.716 inch to the right of LOS. Drop (400) times cosine of 5 degrees (.99619) equals 99.619, subtract that from the drop (100) and get the bullet drop from the horizontal; .381 inch. That’s how far below the 5 degree canted LOF is from where it was without cant.


Calculate your own numbers for a 400 inch drop at 1000 yards for the same bullet.
 
Last edited:
Is this "apples' vs. "oranges"? - I see a diagram , fig. 3, showing the trace of a bullet rising above the line of sight to max height then in the same plane falling forward into the target.

Is "line of fire" the same as a projection of the axis of the bore towards the vertical target plane?; if so figure 3 makes no attempt to do this. To hit the target the bore axis has to be angled up.

To me figure 3 is a down range view of the actual trajectory - like up to max height then forward and down to target.

Are we talking about the same figure 3? If so I see no problem with figure 3 because it does not attempt to show "bullet drop at target range" but does show actual trajectory.

I think cant error would be best determined using actual max height above sight line provided the additional flight of the bullet beyond the max height was factored in and a slope determination of the error triangle would do this. Calculating the cant on the basis of drop is at best a gross estimate because it does not represent to actual situation - hitting a target at extended range.

The actual path of the bullet as I understand it would not be the same as "bullet drop at target range" and figure 3 makes no attempt to show bullet drop from where the line of fire (bore axis?) hits the vertical target plane. Any explanation of the error in figure 3 gotta show the difference between the intent of showing trajectory high point and drop below "line of fire".

I think vertical should not be spelled "verticle" as used in drop.

A better target for correction might be the diagram shown in attachment 1
 
Last edited:
Status
Not open for further replies.

Similar threads

ATTHECROSS
  • Locked
What Scope Rings Would Be Good For A Ruger American Rimfire?
Replies
2
Views
829
ATTHECROSS
ATTHECROSS
P89DCSS
  • Locked
Consistent rifle scope fitting
Replies
4
Views
438
jmr40
jmr40
1
  • Locked
What height scope rings do I need?
Replies
9
Views
891
jakk280rem
J
tcoz
  • Locked
Help with red dot mount height
Replies
2
Views
1K
tcoz
tcoz
L
  • Locked
ring height - Remmy 788
Replies
13
Views
652
SwampWolf
S
Back
Top