Ring Height

Discussion in 'Long Range Scopes and Other Optics' started by silvertip-co, Apr 7, 2015.

  1. silvertip-co

    silvertip-co Well-Known Member

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    In 50 yrs of messing with bolt action rifles I always believed that the lowest scope mount that would clear the bolt was the best way to mount a scope. ie The closer the scope height to the bore the better. In re re re reading one of Jack O'Connor's many treatises on the wonderful .270 Win he says something like this " I guess a scope mounted higher would make the .270 shoot flatter a lot further"(paraphrasing). He was discussing the advantage of a 300y zero over having a 200y zero. So I thought Id run it by the experts here for your considered input. High or low mounting for farthest flattest reach?
     
  2. Rich Coyle

    Rich Coyle Well-Known Member

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    Does the height of the rings above the barrel affect trajectory?

    Sixty shots says, “Yes!” Arbitrarily I decided on a single ten shot group at 100, 200, and 300 yards with two scope heights. According to the computer, if you sight in a firearm at, say, two hundred yards with the low or the high sight, it hits dead on at two hundred yards. Novel concept. The fun information is at one hundred yards or three hundred yards. And beyond.

    I used a Savage .223 with the 26" blued (not stainless) barrel for the test. A trigger job brought the pull down to about two pounds. Th scope was 8X - 32X Burris target scope.

    The loads consisted of a 65 grain JLK bullet (.397 sea level ballistic coefficient corrected to .411 for 1100 feet at the Grants Pass range according to the computer), a neck sized, trimmed to length Remington case with a deburred and squared flash hole holding a CCI BR-4 primer. The powder charge was 27 ½ grains of VarGet. The cases had a weight tolerance of .2 grains and have been fired four times. The average velocity for the first thirty was 3,221 feet per second with a standard deviation of twenty-one.

    The HIGH rings: scope 2.2" above the bore. The temperature started at forty-two degrees and went up to forty-eight degrees during the four hour session. All shooting was done at 32X. The targets were five eights inch squares.

    The Burris settled on the left two hundred yard target, where it was zeroed, to start. The first five shots appeared to make a group that looked more like a one hundred yard group in the square. I admired the group awhile through the scope. Even considered putting up another target. Being more lazy than vain, I continued shooting until the ten shot group was completed. Three of the next five went inside the original five, but a couple made holes on either side of it. The two hundred yard group had a vertical dispersion of only one half inch. Horizontally it opened up to one and eleven sixteenth inches.

    Next I went to the one hundred yard target; leaving the zero setting for 200 yards. Shot number seven opened the one hundred yard oval shaped group to five eighths inch. Measuring from the center of the target up to the center of the group showed .63" on the caliper. The program said it would be .86"....not too bad.

    At three hundred yards, the ten shot group consisted of a round one and eleven sixteenth inches. The three hundred yard group was 5.5 inches low with the 200 yard zero. Barnes said it would be down 5.58 inches.

    The LOW rings: scope 1.68" above the bore.
    The rifle was cleaned and resighted at two hundred yards. The ten shot group of was an enjoyable 1 3/16" group at two hundred yards. Now to the verification groups.

    At three hundred yards the first eight shots were looking good for a factory rifle: 1½ inches. Number nine and ten were on either side opening it up to 2 5/16". It was 5.94 inches low. The 1.68 inch sight height centered 7/16" lower than the 2.2" sight height.

    Moving onto the one hundred yard group: It was great! All ten shots went into a group of less than a half inch, which could be covered with a penny! The group was one inch above the line of sight. The program said it would be 1.12" high. There is only 1/8" discrepancy between the shooting and the program. There was about 3/8" between the impact points of the high and low rings at one hundred yards. The high rings hit lower...or was that the low rings hit higher?

    In the book GAME LOADS AND PRACTICAL BALLISTICS FOR THE AMERICAN HUNTER, Bob Hagel suggests that we sight our varmint rifles in to hit one inch high at one hundred yards. I did that exercise in the computer. The high rings required an impact point of two hundred nine yards. The low rings needed a sighting of one hundred ninety-three yards. Shots from the HIGH rings would impact .29 inch HIGH at two hundred yards. For the LOW rings, the computer had the bullets hitting .24 inch LOW at two hundred yards. That's more than ½ inch . At three hundred yards, it’s more of the same. The high rings are punching holes 5.15 inches low and the low rings are down 6.20 inches. That's more than one inch higher for the same rifle shooting the same bullet at the same velocity under the same conditions.

    Perhaps the outer limits for the .223 could be extended. Another computer generated range estimate: Three hundred fifty yards. The high rings impact 9.83" low, while the low rings come in at 11.14" down with the 200 yard sighting. For the lower sight to approximately match the higher sight over a three-hundred yard course of fire, one needs almost one hundred feet per second additional velocity....according to BARNES.

    In conclusion, what can we conclude? The high rings shoot closer to the line of sight both; before and beyond the range for which they are sighted. That means flatter trajectory without higher velocity.
     
  3. FearNoWind

    FearNoWind Well-Known Member

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    Now let me see if I've got this right.
    Did ya'll say that, all things being equal (same rifle, same scope, same mounts - we only mount the scope higher on the rifle - same rest, etc.) mounting the scope further away from the center of the bore results in better accuracy through improved trajectory? I can't wrap my head around the scope having an effect on trajectory. What am I missing here?
     
  4. Rich Coyle

    Rich Coyle Well-Known Member

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    Accuracy remains the same. The trajectory, with higher rings, appears to flatten somewhat, as postulated by Jack O'Connor and documented by my shooting.
     
  5. FearNoWind

    FearNoWind Well-Known Member

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    Meaning no disrespect to the source(s) of this theory, the physics just don't add up.
    "Tajectory" is the bullet's path toward the target. The bullet's path is a factor of the physical influences (force applied, barrel dynamics, the angle of the barrel relative to the horizon, etc.) and that doesn't change just because I move the scope further away from the center line of the bore. If every aspect of a series of loads is identical and the rifle's placement and physical characteristics remain unchanged, the projectile can be expected to print in exactly the same place with every shot - atmospheric influences excepted of course. Think of it this way. When you sight in your rifle, you adjust the scope to line up with the point at which the rifle prints on target. You don't keep testing loads until you find one that puts the holes where you are holding the cross hairs. :D
     
  6. Rich Coyle

    Rich Coyle Well-Known Member

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    Meaning no disrespect to the source of your theory, the physics don't contradict real life experiments. All you have to do to disprove your theory is run the exact load at the exact velocity in JBM and use 1.5" scope height and a 2" scope height. Don't argue until you have either done that or spent three hours testing it with one rifle using one load with the same scope mounted in different height rings on the same day in the same atmospheric conditions.

    Again no disrespect intended. A few years after I did my test Barnes ran a test and, guess what, they came up with the same results!
     
  7. bruce_ventura

    bruce_ventura Well-Known Member

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    There is no mystery here. It's the same bullet trajectory either way.

    The taller rings move the point of impact down by 0.5". When you dial in 0.5" of bullet up to get back to the same zero at 100 yds, that also raises the POI at longer ranges. Compared to the POI with the shorter rings, the taller rings raise the POI by 0.5" at 200 yds, 1" at 300 yds, etc. It's just simple geometry.

    Or you could just use the lower rings, raise the POI another 0.33" at 100 yds, and get the same drop at 300 yds that you would have gotten with the higher rings.
     
  8. Buttermilk

    Buttermilk Well-Known Member

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    What is easily overlooked: actual bullet path stays the same with either scope height. However, what does change is the eye position or line of sight.

    Moving this LOS up or down in relation to bullet path is what makes the trajectory "flatter".

    It really is simple physics.
     
  9. Rich Coyle

    Rich Coyle Well-Known Member

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    Your post took the mystery out of it. I did what you suggested with JBM. I couldn't cut out the rest, but if one looks at the first column after the yards, it shows what you said.

    Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
    (yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
    50 -0.1 -0.1 0.1 0.2 3596.6 3.221 3044.1 0.041 7.2 13.8
    100 0.7 0.6 0.4 0.4 3488.7 3.125 2864.2 0.083 14.7 14.0
    150 0.7 0.5 1.0 0.6 3383.6 3.031 2694.2 0.127 22.4 14.2
    200 -0.0 -0.0 1.8 0.9 3281.1 2.939 2533.5 0.172 30.3 14.5
    250 -1.5 -0.6 2.9 1.1 3181.2 2.849 2381.5 0.219 38.5 14.7
    300 -3.9 -1.2 4.2 1.3 3083.5 2.762 2237.5 0.266 46.9 14.9
    350 -7.2 -2.0 5.7 1.6 2988.1 2.676 2101.1 0.316 55.6 15.2
    400 -11.5 -2.7 7.6 1.8 2894.7 2.593 1971.9 0.367 64.6 15.4
    450 -16.8 -3.6 9.7 2.1 2803.3 2.511 1849.4 0.420 73.8 15.7
    500 -23.2 -4.4 12.2 2.3 2713.8 2.431 1733.2 0.474 83.4 15.9
    550 -30.8 -5.3 15.0 2.6 2626.1 2.352 1623.0 0.530 93.3 16.2
    600 -39.7 -6.3 18.1 2.9 2540.2 2.275 1518.4 0.588 103.5 16.5
    650 -49.9 -7.3 21.5 3.2 2455.8 2.200 1419.2 0.648 114.1 16.8
    700 -61.5 -8.4 25.3 3.5 2373.0 2.126 1325.2 0.710 125.0 17.1
    10/04/15 21:44, JBM/jbmtraj-5.1.cgi


    Calculated Table
    Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
    (yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
    50 0.1 0.1 0.1 0.2 3596.6 3.221 3044.1 0.041 7.2 13.8
    100 1.0 0.9 0.4 0.4 3488.7 3.125 2864.2 0.083 14.7 14.0
    150 1.2 0.7 1.0 0.6 3383.6 3.031 2694.2 0.127 22.4 14.2
    200 0.6 0.3 1.8 0.9 3281.1 2.939 2533.5 0.172 30.3 14.5
    250 -0.8 -0.3 2.9 1.1 3181.2 2.849 2381.5 0.219 38.5 14.7
    300 -3.0 -1.0 4.2 1.3 3083.5 2.762 2237.5 0.266 46.9 14.9
    350 -6.2 -1.7 5.7 1.6 2988.1 2.676 2101.1 0.316 55.6 15.2
    400 -10.3 -2.5 7.6 1.8 2894.7 2.593 1971.9 0.367 64.6 15.4
    450 -15.5 -3.3 9.7 2.1 2803.3 2.511 1849.4 0.420 73.8 15.7
    500 -21.7 -4.2 12.2 2.3 2713.8 2.431 1733.2 0.474 83.4 15.9
    550 -29.2 -5.1 15.0 2.6 2626.1 2.352 1623.0 0.530 93.3 16.2
    600 -37.9 -6.0 18.1 2.9 2540.1 2.275 1518.4 0.588 103.5 16.5
    650 -48.0 -7.0 21.5 3.2 2455.8 2.200 1419.2 0.648 114.1 16.8
    700 -59.5 -8.1 25.3 3.5 2373.0 2.126 1325.2 0.710 125.0 17.1
    10/04/15 21:46, JBM/jbmtraj-5.1.cgi
     
  10. FearNoWind

    FearNoWind Well-Known Member

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    lightbulbOK Bruce and Buttermilk, thanks a lot. I think I'm beginning to understand where the my confusion lies. Because the bullets arc crosses the line of sight twice on its way to the target, elevating the sight makes it necessary to adjust the angle of the muzzle.
    The actual bullet trajectory remains relatively constant but because, with elevated sights, the bullet's initial path is at a greater angle as it intersects the line of sight the trajectory (relative to line of sight) is said to change. I'm no engineer and it's been a long time since math class; I hope I've got all that right.
    I'm comparing the geometry to what happens when we adjust the ladder sights on a military rifle. There are two "zero" points on the bullet's path; the first at the point where the bullet initially crosses the line of sight and the second where the bullet meets the target.