Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Hunting > Long Range Hunting & Shooting

Long Range Hunting & Shooting Nightforce Optics


Reply

Long Range shots - elevation right on always to the right

 
LinkBack Thread Tools Display Modes
  #43  
Old 08-25-2011, 07:17 PM
Platinum Member
 
Join Date: Apr 2005
Location: Alaska
Posts: 3,368
Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by fatrack View Post
Phorwath,

So the output from your ballistic program shows the same correction regardless of direction of fire? It is my understanding that programs with a correction for Coriolis have an input for bearing and I would wonder why they have this if it makes no difference on the correction?
Yes - it does for the horizontal component of Coriolis drift.

The input for the bearing of the direction of fire (Azimuth) is necessary to determine the vertical component of Coriolis drift, because the vertical drift is maximized when shooting true east or west (90 or 270 degree bearings - parallel to the earth's direction of rotation). The vertical component of Coriolis drift diminishes to zero vertical drift when shooting true north or south (0 or 180 degree bearings - perpendicular to the earth's direction of rotation). Latitude is essential and required to calculate both the horizontal and vertical components of Coriolis drift. The bearing of the direction of fire (Azimuth) is only required to calculate the vertical component of Coriolis drift. (Ballistics software programs might require the input before calculating the horizontal component, but the LoadBase3.0 software yields the same magnitude of horizontal Coriolis drift no matter what bearing I enter.)

What hasn't been mentioned is that in the Northern Hemisphere, horizontal Coriolis drift is always rightward. But in the Southern Hemisphere, horizontal Coriolis drift is always leftward. So in the Northern Hemisphere horizontal Coriolis drift is additive to the bullet's rightward spin drift, for a larger combined rightward drift. If we took our right-twist rifled barrels to the Southern Hemisphere, the bullet's Spin Drift would still be rightward, but the Coriolis drift would now be leftward, offsetting and reducing the combined horizontal drift.
Reply With Quote
  #44  
Old 08-25-2011, 11:50 PM
Gold Member
 
Join Date: Jan 2009
Location: GSP, SC, USA
Posts: 623
Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by phorwath View Post
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.
10x--That's good enough for Gov. Work


Paul to finish this 'Drift course 404' you need to cover one final ADD ON to the OP's situation.
Please cover the additional doping to compensate for a constant 10 MPH 90 degree Right to Left wind and how his 200 gr Nosler Accubond will climb up and over some of those mean air mollies that keep dragging on the right side. I ain't smart enough to figure that, but if old timers ain't kicking in, I think I saw it some where in my other life (when I was younger) that the POI will rise and would the 0.635 MOA of rightward drift be a little bit less because of this drag?
__________________
Son, The first shot is the important one - the others just make him run faster! Grandpa 1949
NRA Life Member 1970
Reply With Quote
  #45  
Old 08-26-2011, 01:39 AM
Platinum Member
 
Join Date: Apr 2005
Location: Alaska
Posts: 3,368
Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by T3-OleMan View Post
Paul to finish this 'Drift course 404' you need to cover one final ADD ON to the OP's situation.
Please cover the additional doping to compensate for a constant 10 MPH 90 degree Right to Left wind and how his 200 gr Nosler Accubond will climb up and over some of those mean air mollies that keep dragging on the right side. I ain't smart enough to figure that, but if old timers ain't kicking in, I think I saw it some where in my other life (when I was younger) that the POI will rise and would the 0.635 MOA of rightward drift be a little bit less because of this drag?
I researched the affect of left and right crosswind-caused vertical drift several years ago, but didn't relegate it to memory, because the quantity of up or down drift was deemed inconsequential for large game hunting. We've already heard from some members that either don't believe in Spin drift or Coriolis drift, or they consider the magnitudes of these sources of drift to be de minimis - insignificant. I don't delegate either Spin or Coriolis drift to de minimus status. But I do delegate the crosswind-caused vertical drift that you refer to - to de minimis status. Interestingly enough, I have read that some long range bench rest competitors commonly dope for this source of vertical drift. When the thickness of a few human hairs separates the winner from the rest of the competitors, I guess every little advantage counts.

Your question caused me to run some strong crosswinds through my LoadBase3.0 ballistics software, and I can officially state that it produced no affect on the predicted magnitudes of Spin Drift. My guess is there's no programming built into LoadBase3.0 software, or any other small arms ballistic software, for purposes of calculating or compensating for this relatively minor source of bullet drift.

However in the process of playing with my ballistics software, I learned that a 10 mph headwind will increase Spin Drift by approximately 0.2 inches at 1000 yds (from 6.6 inches to 6.8 inches) and a 10 mph tailwind will decrease Spin Drift by the same amount. A torrid 60 mph head wind will increase Spin Drift at 1000 yds by about 1.3 inches (from 6.6 inches to 7.9 inches), whereas a 60 mph tailwind will decrease Spin Drift by about 1.1 inches at 1000 yds. Not necessarily all that useful in real life hunting scenarios, but interesting non-the-less. I suspect the primary reason for the increased and decreased spin drift is due to the slightly increased and decreased times of flight, compared to windless conditions. The bullet's Spin Drift is effective for a slightly increased or decreased time-in-flight.

We haven't heard from the OP for quite a few Posts now. I hope we didn't put him into an information overload-caused state of mental stupor. At this point, he can accept that Spin and Coriolis drift could largely be responsible for the rightward drift, or take a pipe bender to his scope tube or barreled action and bend the drift in the opposite direction...

At least a few of our members concur with tweaking the curvature of the scope tube. Not to change the subject, but I have heard it rumored that Osmosis can cause bullet drift... Seriously!. . .

Last edited by phorwath; 08-27-2011 at 02:47 PM.
Reply With Quote
  #46  
Old 08-26-2011, 09:08 AM
Silver Member
 
Join Date: Jul 2010
Posts: 420
Re: Long Range shots - elevation right on always to the right

An interesting point for those that are skeptical about spin drift. PO ACKLEY has a small section dedicated to it. It is a valid anomoly, with numerous variables. Often real observations on bullet flight are counterintuitive. I don't feel that it is of much value for hunting, but for target shooting at the same shooting club with consistan prevailing winds I believe it is demonstrateable and factored into trajectory whether the shooter knows it or not, because no matter what the physics behind these curious bullet flight devations are, we still only have 1 correction available and that is windage and elevation adjustments. As far as the earth spinning goes remember that you are already spinning with the earth and the difference between you and the taget velocity is about zero no matter which direction we shoot, unless you are firing a long range Big Bertha mounted to 3 rail cars. Coriolus, well just take a look at the next tornado you see on television or ask a pilot about course corrections. These things are real science but once again they will be overlooked and compensated for and only of value to those looking for a better understanding of a bullets flight. Of more importance and very much overlooked by the LR multiple distance hunter is simply total bullet length and design. Once a person learns to deliberately adjust his optics out of focus he will start seeing the actual bullet in flight. Long range bullets look like a snake crawling over a sewer grate for about 150 - 200yds. short range bullets go to sleep perhaps as close as 30 yds. I do not give any consideration to a long range bullets behavior for the first 300 yds. and honestly tell people not to even waste time trying to figure out long range behavior with close range observation because there will be no fruit just confusion.
Reply With Quote
  #47  
Old 08-26-2011, 02:12 PM
Platinum Member
 
Join Date: Apr 2005
Location: Alaska
Posts: 3,368
Re: Long Range shots - elevation right on always to the right

For NVH1,
I hope you sort out the issues with your rightward bullet drift. As others have mentioned, the equipment needs to be set up and functioning correctly. It's pretty darn important that you not be canting your rifle. I use anti-cant bubble level devices on my rifles to help ensure I'm not canting the barreled action clockwise or counterclockwise. On uneven ground, like on hill sides and mountain sides, I was surprised to learn how much cant I was causing just relying on my eyes' sense of vertical and horizontal - after I added the anti-cant device to my rifles. Canting the rifle can be a large source of bullet drift.

And to be really sure the drift you're experiencing is real, it's important to shoot on windless days, since as mentioned, even a 1 mph cross wind will cause drift to the extent that you've experienced.

A big reason I think your equipment is set up and functioning close to correct, is that the quantities of drift you've experienced are pretty much in line with what one should expect to see if all equipment is set up perfectly, functioning perfectly, and cant free. So I suspect Spin and Coriolis drift explain the majority of your experienced drift.

Honestly, I don't understand why every long range shooter doesn't experience the same thing you've just encountered. It's the first thing I experienced when I stepped back to 1000 yards and started finding points of impact 10" right of my point of aim, when my 300 yard zero was dead nutz on - left and right. I shot a few more times at both 300 yards and 1000 yards again. What sealed my conclusion was when I was able to shoot in a light snow fall, and I could confirm the environment was wind free over the entire 1000 yard range from the rifle to the target. I even walked the range to observe the snow falling straight down. At that point I posted a Thread on this Forum as you have, requesting assistance in identifying the source of rightward drift.

One of my two rifles didn't have the scope tube mounted correctly aligned with the barreled action. It was causing excessive rightward drift. After I corrected that problem, mounted the anti-cant devices and shot some more, both rifles produced around 9 to 11" of rightward drift. To get the rifles to print on the money at 1000 yds, I had to adjust my zero at 300 yds to hit about 1 inch left.

So I researched and researched and learned about Coriolis and Spin Drift. Acquired some ballistic software. Low and behold, the rightward drift I experience is just about exactly as predicted and accounted for with Coriolis and Spin Drift - when combined. I live at 60 degrees North Latitude, and Coriolis drift is just a little greater here than at 45 degrees Latitude. Finally, some peace of mind.

I have since experienced Coriolis and Spin Drift repetitively, with additional rifles. I suspect the reason some members fail to experience these sources of drift is because their equipment isn't set up or functioning properly, it's commonly too windy where they shoot to be able to discern these sources of drift from the cross wind-caused drift, or they have a natural cant to their rifle that by luck or happenstance, happens to offset these sources of drift.

Once a shooter recognizes and accepts these sources of drift, there are any number of ways to account/dope for them. At that point, the methods for doping for them is largely a matter of personal preference.

Hope all the chatter here didn't scare you away. Good luck.

Last edited by phorwath; 08-27-2011 at 02:51 PM.
Reply With Quote
  #48  
Old 08-26-2011, 03:22 PM
Silver Member
 
Join Date: Apr 2009
Posts: 183
Re: Long Range shots - elevation right on always to the right

After reading through this all again I see you are using a one piece tally base. I would bed the base. That will be the cheepest thing to check first unless you have another scope you can try.

I do believe in spin drift and corialis. I don't see how that can be the problem if your left 3/4 of an inch at 100 yards at 200 your sighted in and at 400 your right 4 inches already.
Reply With Quote
  #49  
Old 08-26-2011, 06:32 PM
Platinum Member
 
Join Date: Apr 2005
Location: Alaska
Posts: 3,368
Re: Long Range shots - elevation right on always to the right

I find it a little easier to establish confidence in my POIs at longer ranges, rather than relying on 1/4" to 1/2" anomalies showing up at 100 yards. Some long range bullets require 200 to 300 yards of downrange travel in order to stabilize. I personally don't even bother shooting at 100 or 200 yards when zeroing my rifles, or fine tuning reloads and shooting for groups. I start at 300 yards. Other experienced members on this Forum suggest 300 to 500 yards as a good initial, minimum testing range for load workups for LRH. Lets the bullets fully stabilize. Also, a 1/4 inch shooter error at 100 yards adds a lot more error into the troubleshooting and diagnostic process than a 1/4 or even 1/2 inch error at 300 yards.

Place priority and more confidence in your down range POI's from 300 yards on out. If I solely shoot for groups and POIs at 300 yards and then at 1000 yards, I have found that to be sufficient to develop and finalize my LRH loads. The ballistics software and pre-printed dope charts can then cover the intermediate ranges between 300 and 1000 yards. Unless I plan on shooting to ranges greater than 1000 yards. For my hunting, the majority of the time I'm content if I've confirmed my rifle's zero and performance out to 1000 yds.

Last edited by phorwath; 08-26-2011 at 11:29 PM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: Long Range shots - elevation right on always to the right
Thread Thread Starter Forum Replies Last Post
My long range rifle and first shots jkward Long Range Hunting & Shooting 5 04-17-2010 12:28 PM
Ethical long range shots? dicktaylor How To Hunt Big Game 23 07-29-2008 11:42 AM
Help: Gun vs.Target - steep shots, barometric adjustments with big elevation change? WildcatB Rifles, Bullets, Barrels and Ballistics 17 03-04-2008 07:21 PM
First Long range shots reed The Basics, Starting Out 6 01-02-2008 06:43 PM
Effects of Mirage on Long Range Shots Bud Meadows Long Range Hunting & Shooting 8 03-21-2004 10:34 PM

Current Poll
Do you watch outdoor shows live or by recording them?
Always recorded - 13.07%
112 Votes
Mostly recorded - 24.27%
208 Votes
Sometimes recorded - 15.05%
129 Votes
Rarely or never recorded - 47.61%
408 Votes
Total Votes: 857
You may not vote on this poll.

All times are GMT -5. The time now is 02:42 AM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC