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Scope Height Above Bore

4K views 11 replies 9 participants last post by  LeShaghal 
#1 ·
I know how to measure the scope height above bore when the scope is mounted level, but.....where does one measure this height when a canted rail/rings are used?

Example, 30 MOA rail, this cants the scope down towards the muzzle. Measure at the front ring, turret or where the reticle is located in the erector tube (if you know where it is)?

Using a ballistic program I realize that scope height doesn't change trajectory that much, if you are close, but does make a difference at long range.

Just curious.
 
#3 ·
The article didn't answer the question for me, because with canted rings, the front and rear of the scope are at different heights. I've always used the center of the scope tube and found the ballistic calcs to be good. But I admit I have not looked for extreme precision at ultra long distance.

I await a really good answer as well.
 
#4 · (Edited)
Further reading shows measurements being made from centerline of bore to center of objective lens.
Also center of bolt to center of turrets, and center of chamber/bolt face to center of scope tube.
Apparently all work well enough for the ballistic calculator to produce usable results.

I'd use the distance from center of chamber at the breach to center of scope tube.
That's where the rear of the cartridge ends up, every time, so it's a constant reference.
 
#5 ·
My personal method is to measure from the chamber to centerline of front scope ring.

This is one area where close enough is close enough. Seriously. You won’t notice a quarter inch height difference on target with a 22, I don’t care how far out you’re shooting. Waaaaay too many other variables have a far greater effect.

For example, my rifle is zeroed at 50 yards with SK Long Range Match. Using Strelok Pro, I have plugged in a scope height of 1.6 inches. If I plug in a target distance of 350 yards (and zero wind) Strelok Pro says I need to Come up 16.3 MRAD.

If I plug in a scope height of 1.85 inches, it tells me to come up 16.2 MRAD.

So, a difference of 0.1 MRAD at 350 yards. That is 1.26 inches at 350 yards. Totally insignificant, considering the other variables such as humidity, wind, muzzle velocity, and not to mention the mechanical accuracy of my rifle system.

Move it out to 500 yards, the quarter inch difference is still only 0.1 MRAD, or now 1.8 inches on target.

Now let’s make it a it a half-inch difference in scope height: at 350 yards, we get an on-target difference of 0.2 MRAD, or 2.5 inches. Significant? Nah.

Alright, so let’s throw in the variable of wind. You’d be surprised how much wind impacts elevation with a little 22. Also, best we can do with wind is measure where our anemometer is, and estimate everywhere else.

So, catch this: 4 mph wind from 64 degrees will require an additional 0.1 MRAD UP from my no-wind zero. If the wind is 6 mph, I need 0.2 MRAD UP from my no-wind zero.

See the point? Just measure your scope close enough and then go shoot. :bthumb:
 
#9 ·
My personal method is to measure from the chamber to centerline of front scope ring.

This is one area where close enough is close enough. Seriously. You won't notice a quarter inch height difference on target with a 22, I don't care how far out you're shooting. Waaaaay too many other variables have a far greater effect.

For example, my rifle is zeroed at 50 yards with SK Long Range Match. Using Strelok Pro, I have plugged in a scope height of 1.6 inches. If I plug in a target distance of 350 yards (and zero wind) Strelok Pro says I need to Come up 16.3 MRAD.

If I plug in a scope height of 1.85 inches, it tells me to come up 16.2 MRAD.

So, a difference of 0.1 MRAD at 350 yards. That is 1.26 inches at 350 yards. Totally insignificant, considering the other variables such as humidity, wind, muzzle velocity, and not to mention the mechanical accuracy of my rifle system.

Move it out to 500 yards, the quarter inch difference is still only 0.1 MRAD, or now 1.8 inches on target.

Now let's make it a it a half-inch difference in scope height: at 350 yards, we get an on-target difference of 0.2 MRAD, or 2.5 inches. Significant? Nah.

Alright, so let's throw in the variable of wind. You'd be surprised how much wind impacts elevation with a little 22. Also, best we can do with wind is measure where our anemometer is, and estimate everywhere else.

So, catch this: 4 mph wind from 64 degrees will require an additional 0.1 MRAD UP from my no-wind zero. If the wind is 6 mph, I need 0.2 MRAD UP from my no-wind zero.

See the point? Just measure your scope close enough and then go shoot. :bthumb:
I'm glad you typed that out. I couldn't agree more.
 
#8 ·
If it works for him, great, but he is touting using a lower jaw rest for stock weld. Problem there is just how much your jaw is open or closed or clenched.

I can work, but takes more time to gain consistency. The cheek bone is always in the same place. If you need to tilt your head as he states, then maybe you need a better adjustable comb that gives left right offset as well, like trap shooters use.

He doesn't address the scope height question as asked here at all.
 
#10 ·
I've never found a ballistic program to be that accurate anyway. For a .22 they are IMO a complete waste of time. Just find the best ammo and then create your own chart of scope settings for 25, 50, 100, 150, 200 etc. by actual shooting.

Then you really know.

As for scope height, I want a cheek-weld when shooting a shotgun and for nothing else. For all rifle shooting I'll take a high scope any day.
 
#11 ·
SavagePlinker said:
I've never found a ballistic program to be that accurate anyway.
+1

It's easy to see they make certain assumptions by looking at inclined shooting angles. They report the exact same trajectories when shooting uphill and downhill. In reality, they're not the same.

Imagine an exaggerated scope/bore angle of 5 degrees difference. If the scope is aimed uphill 45 degrees - the bore is aimed uphill 50 degrees. If the scope is aimed downhill 45 degrees - the bore is aimed downhill 40 degrees. Put 50 up and 40 down in your calculator and you'll see a huge trajectory difference.

The assumption the calculators make is that the scope and bore are parallel. Of course they're not, or you'd hit low at every distance from the bore.

I haven't checked 22lr trajectory differences with actual scope/bore angle corrections, but I did with a 30.06 trajectory. The difference in POI at 300 yards up/down at 45 degrees was under 1/4". Because the scope/bore angle is VERY tiny, the zero angle calculator assumption is "good enough".

Likewise, it doesn't really matter much where you measure the scope height above bore. It just needs to be center-to-center as best as you can measure.
 
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