Originally Posted by WildRose
Then let's correct your information.
Your computations make a lot of assumptions vs what information we have been given to work with.
They are only correct if we assume the shots are fired perpendicular to the rotation of the earth.
That is why I asked him to get us a compass reading on the direction he's shooting so we have more information to work with.
Correct what information? Again, you'll have to further explain yourself. I provided all of the impacting assumptions that were used as input data in order to calculate the magnitude of horizontal Coriolis Drift at both 1000 yards and at 1 mile. My computations are correct for the input parameters I identified and used. If those assumptions don't match the specific conditions of the original poster, are you trying to say my information is incorrect? Here's the information I posted in Post #20:
Coriolis Drift: Input Parameters
Location = 45 Degrees North Latitude
Direction of Fire = Due East or Due West (90 or 270 Degree Azimuth)
Coriolis Drift at 1000 yds = 2.5 inches rightward drift
The Latitude location I provided and used was 45 Degrees North Latitude. The Direction of Fire was I provided and used was Due East or Due West, parallel to the rotation of the earth's rotation. And the Coriolis drift at 1000 yds is correctly calculated as 2.5 inches of rightward drift.
You've stated your understanding and position that Coriolis Drift only causes horizontal bullet drift when the direction of fire is true North (Azimuth of 0 degrees) or true South (Azimuth of 180 degrees), perpendicular to the earth's direction and path of rotation. Your understanding, and resultant position, is mistaken. Which is why you end up with incorrect conclusions, and make incorrect statements.
Coriolis caused horizontal drift is present regardless of the direction of fire, and the magnitude of the drift is determined by the location (Latitude) of the shooter on the earth's surface. The magnitude of horizontal Coriolis drift is greatest at the north and south poles, and diminishes to basically zero at the equator. I chose to use a location half the distance between the north pole and the equator, which is representative of much of the contiguous 48 States.
The compass direction isn't a factor. The information the OP would need to provide is his Latitude location. How many degrees North or South Latitude. And the Latitude is only necessary for the calculation of Coriolis drift. The calculation for the much greater source of drift, Spin Drift
, isn't dependent on either Latitude or the direction of fire.
The OP is seeking an explanation, a cause, a source - for approximately 1 MOA rightward drift out to 1000 yds. What I have explained, calculated, and demonstrated, is that Spin Drift is responsible for 0.635 MOA of rightward drift, and that Coriolis Drift could very easily be responsible for an additional 0.240 MOA of rightward drift. That's a combined rightward drift totaling 0.875 MOA. My question is: Do we really need to be looking for any additional sources or causes of rightward drift? I can't spell it out any clearer. Spin Drift + Coriolis Drift = 0.875 MOA rightward drift at 1000 yds.
Do others still feel compelled to identify the source of the remaining 0.125 MOA of rightward drift based on the limited information we've been provided with thus far? It's a free country and a relatively open Forum. I'm the last person that wants to stand in the way of the exploration and pursuit of all additional potential causes that could produce the remaining 0.125 MOA of rightward drift. Let the fun continue... I'll get popcorn for the kettle... I'm game...