spin drift & Coriolis effect

[Bravo 4]

actually it does alway cause an impact right unless you are in the southern hemisphere in which it will ALLWAYS be LEFT. just as a left spin will cause left drift.
if you dont beleave me shoot out to 1760 yrds and do as you describe. you WILL be WAY off if you try to adjust for a impact left corialis in the northern hemisphere no matter the direction u shoot.

the adjustments i list will get u closer than u can dial anywere in the usa(except alaska), given mean velocity of 2800 fps (a good median for most types of rifles)and bc in the high 5's

At least a couple times a year we shoot our .50's out to a little over 1600 meters, the same mile as your 1760 yards. As a matter of fact that's what we have scheduled this weekend.
When talking about the effects on REALLY long range shooting I believe that I have some pretty knowledgeable resources on the subject. I not only asked our Mortar Platoon SGT (a 20 year 11C), but also five 11C instructors(all MLOC grads, with close to 100 years combined experience).They all said the same thing, you cannot accurately account for Coriolis without a Mortar Ballistic Computer and input the gun's coordinates, the target's coordinates and factor in the bearing from gun to target. You cannot just say it will always land to the right. And these guys shoot out to 7200 meters. I also have a few buddies that are instructors at the Sniper School and they will say the same thing I was told going through the school, you cannot just range a target and put a number on it...you can't just favor/adjust right and call it good.
Now then, the one common factor these guys have in common is they are all Army trained. That could be the down fall of my/their experience...but I doubt it. It if was that easy I bet we would be using it.
As for the 3" right spin drift and 3" right of Coriolis at 1000 yards. I would be willing to say that it's really 6" of spin drift. Looking at the data book for our .50's shooting the MK211 rounds, it shows a .5 MOA of spin drift @ 1000 (also what I use for my .338 Edge). For our M24's most guys I know use .75-1 MOA.

 

[rem]

In Excel the formula for the cell would be:

=1+2*0.00007292*2870/-32.2*COS(RADIANS(45))*SIN(RADIANS(270))

thanks, that is very helpful.

 

[RDM416]

......As for the 3" right spin drift and 3" right of Coriolis at 1000 yards. I would be willing to say that it's really 6" of spin drift. Looking at the data book for our .50's shooting the MK211 rounds, it shows a .5 MOA of spin drift @ 1000 (also what I use for my .338 Edge). For our M24's most guys I know use .75-1 MOA.

Bravo 4,

You are exactly right about just the spin drift being way more than 3" at 1000 yards. According to Bryan Litz book, Applied Ballistics for Long Range Shooting, using two different equations for a .308, 168 grain SMK the spin drift alone will be somewhere between 11.1" to 14.24" with a 1:10 twist barrel, a little less with a 1:14 twist. This would be somewhere between 1 to 1 1/2 moa. The spin drift for a 50 BMG using a 750 grain Amax, 1:15 twist barrel is 6.73" as measured by the military using Doppler Radar. (very accurate data). I have verified this with my 510 Allen Mag, using the same bullet but at a higher velocity (the test was a 2690 and I am running 2850 fps) I am seeing 6" right drift at 1000 yards ( a little over 1/2 moa). I use 1/2 moa for my 338 Khan at 1000, the ballistics program I am using gives it 6" value.

 

[paphil]

I've read this entire thread and am more confused than before I started. First , Corioles has nothing to do with spin drift. It is all about the rotation of the earth and is a very small factor in 1000 yard shooting It is dependant on time of flight and direction. North and south have no effect and east will be high poi and west will have low poi. How much depends on distance and time of flight.
Spin drift is caused by the effect of gravity on the moving ,spinning bullet . when you apply a force to a gyroscope it tends to move at right angle to the force applied. On a bullet spinning right and gravity pulling down, the drift is to the right. The opposite for a left spin.
When you have a wind blowing from the left , the gyroscopic force will make the bullet go right and down. Conversely a wind from the right will make the bullet go left and up. I know many will argue this but real world experience tells me that i should listen to my college physics lessons and the results I have shooting long range cold bore shots. The drift is about 3 1/2 minutes to 1 . You don't get spotter shots on game. Try it next time you shoot in the wind.

Next time you shoot a spotter shot in the wind, , pay attention where it hits. Wind from the left, hit will be low. Wind from the right, the hit will be high!

Found a really good old thread with some actual testing. Vertical Component of Wind Drift

 

[rem]

Here's another resource for spin drift and coriolis effect:
spindrift
-Bryan

Bryan did you come up with all of those equations? I like your article.

 

[tresmon]

Good points bravo.

modern ballistic programs for shooters are nothing more than old mortar & artillery math programs tweaked specifically for the rifle shooter.

Its from this that I got my 3" & 3" reference.
Per your spindrift quotes: spin drift varies with diameter of the projectile, length of projectile and RPM, but the program will not ask for rpm because you will not know... it asks you for muzzle velocity and rifling twist and calculates it for you.

All good stuff!

 

[rem]

I've read this entire thread and am more confused than before I started. First , Corioles has nothing to do with spin drift. It is all about the rotation of the earth and is a very small factor in 1000 yard shooting It is dependant on time of flight and direction. North and south have no effect and east will be high poi and west will have low poi. How much depends on distance and time of flight.
Spin drift is caused by the effect of gravity on the moving ,spinning bullet . when you apply a force to a gyroscope it tends to move at right angle to the force applied. On a bullet spinning right and gravity pulling down, the drift is to the right. The opposite for a left spin.
When you have a wind blowing from the left , the gyroscopic force will make the bullet go right and down. Conversely a wind from the right will make the bullet go left and up. I know many will argue this but real world experience tells me that i should listen to my college physics lessons and the results I have shooting long range cold bore shots. The drift is about 3 1/2 minutes to 1 . You don't get spotter shots on game. Try it next time you shoot in the wind.

Next time you shoot a spotter shot in the wind, , pay attention where it hits. Wind from the left, hit will be low. Wind from the right, the hit will be high!

Found a really good old thread with some actual testing. Vertical Component of Wind Drift

i have read the same thing some where else( wind with spin drift) and it makes complete sense. but does it effect it a lot or a little?

 

[load]

At least a couple times a year we shoot our .50's out to a little over 1600 meters, the same mile as your 1760 yards. As a matter of fact that's what we have scheduled this weekend.
When talking about the effects on REALLY long range shooting I believe that I have some pretty knowledgeable resources on the subject. I not only asked our Mortar Platoon SGT (a 20 year 11C), but also five 11C instructors(all MLOC grads, with close to 100 years combined experience).They all said the same thing, you cannot accurately account for Coriolis without a Mortar Ballistic Computer and input the gun's coordinates, the target's coordinates and factor in the bearing from gun to target. You cannot just say it will always land to the right. And these guys shoot out to 7200 meters. I also have a few buddies that are instructors at the Sniper School and they will say the same thing I was told going through the school, you cannot just range a target and put a number on it...you can't just favor/adjust right and call it good.
Now then, the one common factor these guys have in common is they are all Army trained. That could be the down fall of my/their experience...but I doubt it. It if was that easy I bet we would be using it.
As for the 3" right spin drift and 3" right of Coriolis at 1000 yards. I would be willing to say that it's really 6" of spin drift. Looking at the data book for our .50's shooting the MK211 rounds, it shows a .5 MOA of spin drift @ 1000 (also what I use for my .338 Edge). For our M24's most guys I know use .75-1 MOA.

look all i did was give the answer for the equation (derived from ballistics fte)for 45 degrees lat. at that lat it gets you close enouph from southern arizona to northern idaho. i listed how to quickly vector for east/west asimuth. again i did not say it was perfect but i did say close enouph. if you go closer to equator or to the north pole (notice my comment about alaska)the numbers change and will need new calcs. but for a majority of people in the us these simple numbers work. i did not mention #s for spin drift.

 

[Good]

Tag. I love this stuff.

 

[Punisher]

Why don't we have LH twist barrels?

Left twist, It would only work if you are shooting northward. Shoot south and you've got it. Shoot east or west and the corialis effect changes your flight time.

 

[Punisher]

Like my wife says: "why don't you just... Become a better shot."

 

[Michael Eichele]

Left twist, It would only work if you are shooting northward. Shoot south and you've got it. Shoot east or west and the corialis effect changes your flight time.

North or south doesn't matter. Impact WILL ALWAYS be right in the northern hemisphere.

 

[Punisher]

I understand your point, but lets say you account for all of the variables on your 1000 yard whitetail shot. if your gun shoots 1MOA at 1000 yards you are still very likely to miss the vital area. not to mention 1mph of wind will drift your bullet at least 4"(depending on your caliber fps and BC). I shoot at distances at targets before I ever shoot at an animal at that range. If i have 1.25 MOA worth of drift at 1000 between spin and Coriolis Effect I know exactly what it is because I have shot at that range many times before I will take the shot.

Unfortunately, if my gun only shot 1 MOA, I would not take a 1000 yard shot. I require accuracy of at leat 1/2 MOA to actually pull any shot off.

 

[deadidarren]

Unfortunately, if my gun only shot 1 MOA, I would not take a 1000 yard shot. I require accuracy of at leat 1/2 MOA to actually pull any shot off.

+1...