Home Forums Hunting & Shooting Hunting Optics scope height influence on trajectory

FASTEST IS NOT ALWAYS FLATTEST

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 barrel for the test. A trigger job by Bud Hopson (Lock, Stock, and Barrel, 115 S.W. "H" st., Grants Pass, Ore. 97526 (541) 474-0775) brought the pull down to about two pounds. The scope was 8X - 32X Burris Signature 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 � 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 inches 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 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 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 inches on the caliper. The program said it would be .86 inches....not too bad.

At three hundred yards, the ten shot group consisted of a round group measuring a nice 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. A flier made a 2 inch ten shot group out of an enjoyable 1 3/16 inch nine shot 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: 1� inches. Number nine and ten were on either side opening it up to 2 5/16 inches. It was 5.94 inches low. The 1.68 inch sight height centered 7/16 inch lower than the 2.2 inches 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 inches high. There is only 1/8 inch discrepancy between the shooting and the program. There was about 3/8 inch 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 � 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 inches low, while the low rings come in at 11.14 inches 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.

Im gonna get some popcorn and watch this unfold!

The correct answer is scope height has absolutely nothing to due with bullet trajectory or velocity. Optics do not trump physics and ballistics.

And after he did all that "research"!

It will affect the way the bullet trajectory intersects with the line of sight.

Read what he wrote about his "research". Note the very first line in all CAPS! I don't think that's what he was saying...oh, and the title of the thread is a clue too.

What the hell did I get into?

Want some popcorn...I'm done here 'cept for watchin' and laughin'!

300WinMag,



Your ignorant predjudice is showing. I use it myself at times.

When the height of the scope significantly changes in relation to the bore, it takes longer for the bullet to get to the line of sight in its "upward climb" while it is falling in relation to the bore.

The impacts change because of the laws of physics and ballistics. Not dispite them.

LMAO Anybody got another beer? This might get bloody.

Wayne

That is absolutely true.Sight height won't change the trajectory of the bullet,but it will change where you have to aim,for the bullet to impact where you desire. Use the link below and vary the sight height to prove it.

http://www.eskimo.com/~jbm/calculations/traj/traj.html

Years ago, when my uncle was a young man, he discovered or was told he could sight in his 06 at 25 yds and be on at 100 also. He is down to his final hunting years and struggling to make meat.

Recently, after a series of misses over the last few years, I inquired if he had sighted his rifle lately. He stated that he had a couple years ago and that he did the 25yd thing.
I told him that what was true when he was shooting irons won't be the same now, because his rifle is now scoped and with see through mounts at that. That height above bore had increased and that in any case if he was an inch off at 25 yds he would be 4 inches off at 100 yds.
He of course thinks I'm full of it and a dumb sumbitch to boot....

Sorry, can't let this one go since I have a fair amount of physics education and mama would be disappointed if I didn't use it. Some definitions:

Trajectory: The path of a projectile or other moving body through space.

Velocity: A vector that denotes both the speed and direction a body is moving.



The first part of your statement may be true, but these are apparent observations. The part that says "this means it shoots flatter without higher velocity" is patently untrue. Projectiles with the same energy (powder), and mass (bullet weight) from the same barrel will follow the same trajectory and have the same velocity, except for the minor variances that drive us nuts when we try to shoot tiny groups.

300WinMag,

When a bullet stays closer to the line of sight than another, one can easily say it has a flatter trjectory than one which is further away from the line of sight.

No matter how you try to apply your education here, you are ignoring the fact that a higher sight appears to have a flatter trajectory when both are zeroed at the same range.

Try it for yourself.

True.

By having a higher scope mount, you have effectively increased your "point blank range", as it is often called, because the bullet is starting out further below the line of sight with a high mount than it is a low mount. Picture the trajectory curve...with a higher mount, you are starting lower on the curve, so the bullet can travel further before reaching the maximum height than it would with a lower mount.

The outlaw got it right.

Go to Norma's website and play with their ballistics calculator.

It tain't flatter .... its actually MORE of a rainbow.

True but misleading. The velocity and trajectory remain the same, but there's a distinct difference in the relationship between the line of sight and the path of the bullet.

Physics makes it inevitable and indisputable that the height of the scope axis above the axis of the bore have a slight but definite effect on the relationship between the line of sight and the trajectory of the bullet.

The bullet crosses the higher line of sight farther from the muzzle, both as it rises above the line of sight and again as it drops to and below the line of sight.

The advantage of a higher line of sight is definite but slight.

Ken's explanation is simple & correct.

MM

This I agree with as explained. Even if I didn't, I don't have the physics knowledge to dispute it, but in this case, don't need it. What it seems is not taken in to account by the OP is what becomes of the bullet's path between the first time it crosses the line of sight and the second time. As is commonly said here...there are no free lunches...that ballistic arch will remain the same based on velocity, BC, etc., etc,. and wont change for any given bullet. You can't make a slow bullet shoot flatter by raising the line of sight...you may increase the "point blank range" or think you have, but in reality created such a ballistic arch that your mid range trajectory is so high that it takes you off target at that range. For every projectile at any given velocity, there is an optimal sight height and sight in calculation to give maximum point blank range.

http://www.chuckhawks.com/rifle_trajectory_table.htm