Scope height off the barrel

[RonS]

RonS said:

"The closer to the bore you mount the scope, the closer to on target you will be as your range increases or decreases... given most calibers."

That statement is confusing and not totally true. The further apart the scope to bore the further away the second crossing point will be. It is old knowledge. I read about it in Jim Carmichael's book of the Rifle over 25 yrs ago. The scope and bore are not setup at the same angle. The bore has a higher angle above horizontal than the scope. As a result the aiming point and bullet trajectory will cross twice downrange.




Anyone with a ballistics program can crunch the numbers to see.

Usually the first crossing point is near 25 yds. I decided to see just how much difference there would be and crunched some numbers below:

I used JBM program to compare my 6mm BR's trajectory with a 105 Hybrid at 2843 fps
Elevation is 4000 ft, 59 degrees, 30% humidity etc. Zeroed for 25 yds.

Scope height second crossover point
1.5" 256 yd
1.6" 271 yds
1.7" 287 yds


I don't worry much about what height I place the scope on my bolt action rifles as long as I get a good comfortable cheek weld. I input the height above bore into the JBM program for my trajectory.

I once bought a pair of extra low talley one pc rings and discovered I couldn't comfortably get my face low enough on the bell and Carlson Ti stock to see through a 3.5-10 x 40 Leupold!

Now there's an answer. And a good one. I agree. I use Strelok and punch in the same data. The result being that I'm on paper from 100 out to 1000 yards on the first shot. Unless it's blowing a gale and I missed the wind call but even at that, the elevation is pretty much on.

My answer was oriented toward flat shooting calibers at closer ranges. See it at the range pretty frequently. Someone sights in an AR at 25-50 yards then goes out to 100-200 yards and they're not on paper or steel anymore. They're trying to find out where they are hitting. Very high would be my answer. Take it out further and you might be back on at some point. How far? Depends on a lot of factors not the least of which is the bullet, the velocity and the height of the scope above the bore.

 

[lancetkenyon]

I like my scopes as low as possible to clear the objective bell by a minimum of 1/8", and when I have a comfortable cheek weld. An AR platform has no drop at the comb, so the optics sit a touch higher than a hunting type stock. Same can be said for a tactical type stock.

Comfortable and consistent cheek weld helps increase accuracy for me.

A few examples:
My AR setup (note it is not nearly as high as some would prefer, but it fits me from prone and upright the same) w. Seekins Low (.92") rings for 34mm scope on 1/2" risers (now have a Badger Ordinance 22MOA canted mount that adds 1/2" as well)


My 6.5 SLR w. Seekins 1" high rings for 34mm scope on 20MOA rail. Scope has 56mm objective. I might be switching to the Seekins Low (.92") rings soon.


.300RUM w. Leupold high rings for 300mm scope. Waiting for the elk to arrive.

 

[gohring3006]

I like my scopes as low as possible to clear the objective bell by a minimum of 1/8", and when I have a comfortable cheek weld. An AR platform has no drop at the comb, so the optics sit a touch higher than a hunting type stock. Same can be said for a tactical type stock.

Comfortable and consistent cheek weld helps increase accuracy for me.

A few examples:
My AR setup (note it is not nearly as high as some would prefer, but it fits me from prone and upright the same) w. Seekins Low (.92") rings for 34mm scope on 1/2" risers (now have a Badger Ordinance 22MOA canted mount that adds 1/2" as well)


My 6.5 SLR w. Seekins 1" high rings for 34mm scope on 20MOA rail. Scope has 56mm objective. I might be switching to the Seekins Low (.92") rings soon.


.300RUM w. Leupold high rings for 300mm scope. Waiting for the elk to arrive.

Very nice paint jobs. I have noticed shooting prone you can get a little bit lower on the stock. But its still pretty high compared to a bolt gun.

 

[lancetkenyon]

Very nice paint jobs. I have noticed shooting prone you can get a little bit lower on the stock. But its still pretty high compared to a bolt gun.

Yes, definitely higher than a bolt gun by about 1/2" or so, but with no comb drop, it has to be higher to get behind the scope for me. I don't know if I could go any lower and still have proper sight picture without cramming my face down on the stock.

I close my eyes, and mount the rifle where it is comfortable and consistent. When I open my eyes, sight picture is perfect for me.

 

[FEENIX]

Yes, definitely higher than a bolt gun by about 1/2" or so, but with no comb drop, it has to be higher to get behind the scope for me. I don't know if I could go any lower and still have proper sight picture without cramming my face down on the stock.

I close my eyes, and mount the rifle where it is comfortable and consistent. When I open my eyes, sight picture is perfect for me.

Yep, it don't get no simpler than that! BTW, those are great rigs you have and I agree with gohring3006 on the patriotic paint job. You and WR have some cool toys.

Below is nearly an hour's worth of various scopes mounted on AR (or similar) platform ...



My wife shooting her RRA Operator at http://gfssc.net/ ...

 

[4xforfun]

duplicate

 

[4xforfun]

So no one really answered the question. The answer is that it comes down to a simple question of geometry. Picture a scope mounted 5 inches above the bore and one mounted 1/2 inch above the bore. Shift from a 50 yard shot to a 150 yard shot. Which do you think is going to be closer to on target if the caliber is .223? It's a very simple solution. You'll be shooting airplanes out of the air with a scope mounted 5 inches above the bore... Relatively speaking. The closer to the bore you mount the scope, the closer to on target you will be as your range increases or decreases... given most calibers.[/quot

Lets take my 300 wby shooting 210 vld's. 300 yard zero with BOTH 1/2 inch and 5 inch scope height. All else stays the same.

With the 5" scope height the maximum height of the bullet flight is at around 175 yards, where you are 3 inches high.

With the 1/2 inch scope height, the distance of max height is about the same, but the bullet is now 5 inches high.

lightbulb

 

[just browsing]

I have Seekins Precision Medium .87" rings on my 110 FCP and haven't had any issues. I was considering going to the Low .82" rings but I've been ultra lazy about switching them.

For reference... I can't imagine the .05" is going to make much of a difference: