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bullet drop and scope leveling

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Unread 03-17-2006, 09:01 PM
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Join Date: Dec 2005
Posts: 2,483
Re: bullet drop and scope leveling

The person whom I talked to at Lilja (I cannto remember the name) told me that drilling a hole 34 inches deep and being on center on both ends was near to impossible.

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Something's wrong. Obermeyer and Kreiger have been gun drilling blanks that size with less than a couple hundredths of an inch error at either end. A gun drill automatically centers itself at the center of rotation by the shape of the tool; a long and well established method used by many top barrel makers who get excellent results.

Of course, Lilja had to supply several barrels to a couple of folks on the US Olympic team before they got one that would shoot well. I wonder why...... Maybe Lilja hasn't perfected their gun drilling methods.
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Unread 03-17-2006, 10:44 PM
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Location: on the rifle range in Utah
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Re: bullet drop and scope leveling

I can attest to the fact that the coriolis effect of the earth spinning at different speeds (about 500 yards per second at the equator) depending on latitude is zero.

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I would disagree with this statement. It may be a small amount but it is still there. And the farther you shoot, the more it shows up. I have shot enough at 2000 yards plus to get some calm enough days that there was no other explanation for the phenomenon than for the "C" effect.

Another interesting point was that at 2k, every bullet that went left of the gong usually also shot high, and every bullet that went right of the gong went low.

At what points in the ocean were you shooting from the ships and did you notice a change in Coriolis as you got farther from the Equator?

But I believe that the original poster's problem (if he did truly level his scope properly) was as JBM stated. I have witnessed gyroscopic drift in every bullet fired to one degree or another and it is much more of a factor than Coriolis. If Coriolis makes 1" difference then Gyro makes 9". These are not the real amounts of course, just an example to show the magnitude in each.

If you are leaving your rifle zeroed at 1k for left-right movement and it is always on, then you have "zeroed" the "G" drift out and it may seem non apparent but it is still there although it may be in a small amount. You have simply just corrected for it.
Find it
Range it
Click it
Pull it
Dump it

If it's not far, it's boring.
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Unread 03-18-2006, 07:40 AM
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Re: bullet drop and scope leveling

Rifle shooters have observed the phenomena of bullets going high-left and low-right for a century or more. If a left-hand twist is used itíll be low-left and high-right. Itís most predominant with smallbore 22 rimfire rifles at 100 yards but gets less at shorter ranges. Some left-handed smallbore competitors cant their rifles about 35 degrees to the right so making windage only adjustments will compensate correctly in both axes. Centerfire rifle shooters have noticed it starting at about 800 yards and getting a bit worse at 1000 when some ammo types are used.

Itís caused by cross winds putting different pressure under and over the bullet. A clockwise spinning bulletís surface pulls a wind from the right under it putting more pressure at that point so it moves left and up. The opposite happens with a wind from the left. Smallbore prone shooters will hold towards 4:15-oíclock when wind from the right picks up. Highpower shooters will hold off at 3:15-oíclock for a right wind pick up; the effect is much less than with 22 rimfire at 100 or 50 yards.

As for the coriolis effect on rifle bullets through 1000 yards, it may well exist. But itís so darned small and unimportant that none of the top highpower long range folks I know care about it nor get concerned about correcting for it. I once fired 30 rounds alternating between a 100- and 1000-yard target at 5 AM when the air was so calm and clear I could see bullet holes in the black at 1000 yards. The 15-shot groups at 100 and 1000 yards were centered for windage but the close one was some 40-odd inches high and straight up (measured with plumb line) from the aiming mark. Whatever drift effect there was didnít matter; it wasnít visible.

I donít remember much detail about gun aiming computersí corrections for latitude from my experiences in the late Ď50s. When I changed latitude, bearing and range values running tests on those marvelous mechanical monsters the gun orders in the horizontal plane also changed. How much was for precessional drift and how much was for the earthís rotation now escapes me. One can read about it by going to:
then scrolling down to the section ďCorrecting for the Coriolis Effect.Ē The greater the range the bigger the correction was. More information or large caliber ballistics including the projectileís drift caused by gyroscopic precession or Magnus Effect can be seen at
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Unread 03-18-2006, 09:52 AM
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Join Date: Feb 2005
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Re: bullet drop and scope leveling

I tend to agree with Bart on this as I have not experienced any drift horizontaly out to 1000 yards on calm (no wind) days.
range it,check the wind, dial in correction, aim and only one shot
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Unread 03-18-2006, 12:12 PM
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Re: bullet drop and scope leveling

I agree with the above statement. I routinely shoot up to 978 yards down a 30 foot wide opening through 60 foot tall pine trees that act as a very good wind brake.

I always zero my gun dead nuts right on at 400 yards and then check it on successive days to verify zero. We have even shot 5-shot groups over several days (ie two shots today, two tomorrow and one on the third day that were .5" or better. Afer the 400 yard zero is obtained and confirmed on three different days, we progressively move the drop board out in 100 yard increments to derive drop tables for the particular cartrige. Additionally, I have placed 3/4" maskng tape level across the top of the board and another 90 degress vertical to use as an aiming point.

We have found that the higher BC bullets tend to track closer to the vertical aiming line (ie lesser drift) while the lesser BC bullets travel further away (ie more drift) from the line. In fact during some of our testing last year, we were actually hitting the masking tape at the 900 yard mark when holding dead on. Finally, the bullet drift in minimal wind conditions was so slight with higher BC bullets, anything over a 2" drift was considered a bad shot.

We only shoot to derive the drop tables when it is cloudy or before the sun rays hit the ground causing mirage.

In short, using wind flags with the pine trees blocking the wind and shooting at times when mirage has not started has yeilded some very consistent shooting results. Our most accurate bullets were the Lost River bullets seated with the ogives .020" to .050" away from the rifling. Many times the two shots at each range, the holes were touching all the way out to the 800 yard line. We never got the 900 yard shots to touch. Too bad the Lost River bullets (both poly and metal tipped) do not expand. We found this out the hard way when deer were hit and knocked down only to get up and run off and later killed with healed-over Lost River bullet wounds.

Anyway, we did not see much drift due to spin and we were shooting 8 twist barrels.

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Unread 03-18-2006, 01:04 PM
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Join Date: Sep 2003
Location: Blighty
Posts: 637
Re: bullet drop and scope leveling

We did coriolis to death a while back; can't summon up the will to rehash it here so here's a link:

Drift (or spindrift) is one of the few 'weird and wonderful' ballistic effects observable and measurable at 1000yds...the others (coriolis etc) are all at play, but not measurable. Drift absolutely is.

Itís not yaw, but precession caused by the bulletís tip continuously pointing down as its spin axis stays parallel to the trajectory path. As the bullet noses over, its right-hand twist causes it to change its direction to, or drift to the right.

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...actually, projectiles fly slightly nose up in relation to their trajectory; this means that air resistance will try to lift the projectile's nose. Because the projectile is a powerfully spinning gyroscope it reacts to this upward pressure by yawing slightly to the right (it's just something gyroscopes do), with this new yaw, the changed direction of air resistance causes the nose to move down (again, because of the weird way gyroscopes react to forces)...then it will move left...then it will move up ....and so on round and round.
This creates an effect known as 'nutational rotation' ..a more complex movement than I can describe without drawing a picture.
....anyway, the net effect of all this movement is that (clockwise spun) projectiles average a 'nose high and right' attitude in relation to the line of their trajectory. This 'average orientation' of the projectile known as the yaw of repose. should be obvious why a 'high and right' yaw of repose (also known as 'equilibrium yaw') will cause increased air pressure on the left side of the projectile and thus cause it to drift to the right.

...I think you'll find the values quoted by JBM are the average accepted 'norms'.....take a peek through a direct fire antitank gun sight next time you have a chance; their reticles are actually marked to account for drift...even at relatively short range [img]/ubbthreads/images/graemlins/smile.gif[/img].
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Unread 03-18-2006, 01:37 PM
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Join Date: Jan 2003
Location: The rifle range, or archery range or behind the computer in Alaska
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Re: bullet drop and scope leveling

I once fired 30 rounds alternating between a 100- and 1000-yard target at 5 AM when the air was so calm and clear I could see bullet holes in the black at 1000 yards. The 15-shot groups at 100 and 1000 yards were centered for windage but the close one was some 40-odd inches high and straight up (measured with plumb line) from the aiming mark. Whatever drift effect there was didnít matter; it wasnít visible.

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Sometimes if a shooters scope is not quite level with the rifle and happens to be in the right direction as you click or use hold overs for that matter it compensates for the spin drift leading one to believe that it doesnt exist. I assure you that this is a scientifec fact that spin drift occurs. Whether or not ones equipment is set up correct or not is another story. Personaly I have a right handed twist and know what my drift values are through tests and have my scope ever so slightly off of perfectly plumb. As I use clicks or hold overs it takes the guess work out of holding off to the left. My rifle is level and the level mounted to my scope reads level, but the scope is not quite level.

If you have never experianced spin drift and you were shooting in a DEAD still air enviornment you were none other than lucky to have screwed up mounting your scope and did something right. [img]/ubbthreads/images/graemlins/wink.gif[/img]
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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