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1000 yard question |
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shooter4
Optics Apprentice Joined: February/11/2009 Status: Offline Points: 177 |
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Posted: February/15/2011 at 12:29 |
Gentlemen
Ive been offered to try out a range that is 1000 yds long. Im bringing my 308, zeroed in at 150yds with 168 grain bullet. Nice combo. BUT I have never tried a long shot like that before. I really need to adjust my scope to compensate for bullet drop.
The big question is if I need to compensate for bullet drift as well at these ranges?? Is there bullet spin-drift (left or right?) other than wind drift?
Also, is it true that when turning the up/down adjustment knob on the scope, the crosshairs move slightly (left or right) off target? (depending if you adjust up and down). If so what effect does that lateral movement add up to at say 100 clicks on the scope?
Hope I wont look too stupid when I try out those 1000yds.
thanX
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SVT_Tactical
MODERATOR Chief Sackscratch Joined: December/17/2009 Location: NorthCackalacky Status: Offline Points: 31233 |
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get your data on the bullet your shooting and go to a ballistics calculater, print it out with wind drifts for 5, 10, 15 and 20 MPH
Edited by SVT_Tactical - April/26/2011 at 09:07 |
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shooter4
Optics Apprentice Joined: February/11/2009 Status: Offline Points: 177 |
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That is not what Im asking about. Im asking if some knows if there is a drift on the bullet caused by it spinning - AND if the mechanics of scopes are such that turning the horizontal turret causes the scope to move slightly vertical??
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SVT_Tactical
MODERATOR Chief Sackscratch Joined: December/17/2009 Location: NorthCackalacky Status: Offline Points: 31233 |
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if mounted correctly, the horizontal movement will not move the bullet vertical, and vise versa. If its not mounted straight, then yes it will. One way to test this is at 100yds, shoot once at the bottom of your target, dial in 10MOA up, shoot again at the same spot you aimed at originally, dial 10MOA down and shoot again at the same spot, do that until you have 3 shots at each place, they should be perfectly straight up and down, do the same thing vertically, shoot once, dial 10MOA to the right or left, shoot at same spot....... if the groups are perfectly level you should be good. They make tools and devises to get it but I've used this method with good results.
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biggreen747
Optics Journeyman Joined: October/16/2009 Location: Colorado Status: Offline Points: 470 |
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www.jbmballistics.com will calculate spin drift too..
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We measure it with a micrometer, mark it with a crayon, and cut it with a chainsaw.
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Rancid Coolaid
MODERATOR Joined: January/19/2005 Location: United States Status: Offline Points: 9318 |
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If you are moving from a 150-yard zero to a 1,000 yard shot, my recommendation is don't.
A 1,000 yard shot is not easy, no one can tell you exactly what your dope adjustment will be. Questions of Coriolis effect and spin drift are important considerations, but if you are (and no offense intended) expecting to get educated in a forum or on a 1,000 yard line, this will not go well for you. I recommend you put some time in to understanding your round's ballistics, then trying it at 300-500 and 600-800 if possible. Your questions seem a bit simplistic, which leads me to believe you are new to rifles with optics. Long range ain't easy, and you will not gain what you need to to make 1000 yard shots by talking with people on the internet - no matter how good the people are or how well intentioned you might be.
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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What scope are you using? Yes, you will have a bit of spin drift, but that should be the last of your worries right now. Having enough adjustment at all, compensating for the wind and hoping the bullets are still supersonic at 1000 (what load/velocity/barrel length, etc, do you have and what is the site elevation?) are the biggies.
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jonoMT
Optics Master Extraordinaire Joined: November/13/2008 Location: Montana Status: Offline Points: 4853 |
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Yep, you have a lot more to worry about than the 8" or so that spin drift would impart to a typical .308 load @ 1000 yards. There are lots of cheap scopes that will throw the windage out when elevation is adjusted or vice-versa. So at least make sure you have a decent scope that tracks and returns to zero. Then take the advice above and nail 300 yards before you move to 500, before you move to 750, before you move to 1000. Just speaking from my own experience, I never even tried 600 yards until I'd been shooting at lesser ranges solidly for a couple years.
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Reaction time is a factor...
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Jon A
Optics Journeyman Joined: March/14/2008 Location: Everett, WA Status: Offline Points: 670 |
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Expensive ones too! |
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Griffin99
Optics Apprentice Joined: September/19/2005 Location: Lawton, OK Status: Offline Points: 83 |
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My day job is an artillery officer. There is a portion of our certification called manual gunnery, where you get to do all of the calculations that a ballistic computer does by hand. First off, a couple of points.
1) Rancid Coolaid gives great advice for you. You can get an idea of what you need via a forum, but you actually have to shoot that distance with your rifle,bullet,scope combination to get your actual data for that setup. A forum or ballistics computer can only give you an idea of what to expect. 2)jonoMT and Jon A are spot on as well about drift. Since we use predominantly right hand twist barrels (155mm and 105mm howitzers are the same) the projectile will drift to the right. At the range of 1000 yds, however, the effect is negligible at best. 3) also, at 1000 yds, though Hollywood loves to misuse the Coriolis effect. When you start getting out past 3000 meters, you begin to take the rotation of the earth into effect. If you start shooting extreme long range, that might begin to be a factor. In artillery, we use a manual (among many) called a Tabular Firing Table, or TFT for short. This manual has data for shell type, fuse type, powder charge and type for the series of cannon tubes that we use. These tables are built around "standard conditions," just like the ballistic software out there. For example, the standard conditions of the TFT are Weather: 1) Air Temp 100% (59 degrees F) 2) Air density 100% (1225 gm/m cubed) 2) No wind Position: 1) Gun, Target, and Meteorological Datum Plane at the same altitude. 2) Accurate range 3) No rotation of the earth Material: 1) Standard weapon, projectile and fuze 2) Propellant Temperature (70 degrees F) 3) Level Trunnions and precision settings 4) Firing table muzzle velocity 5) No drift That is our base line when we look at the TFT. Your ballistic software has to have standard conditions similar to these to even begin to give you an idea of how your bullet is going to act in flight. Every ballistics software has a disclaimer (long and boring to read) that will essentially say that the figures you are getting are based off of whatever standard conditions they set in their software and should be used as a guide rather that actual data blah blah blah. What you are trying to do with your rifle at 1000 yards is the same thing I am trying to do at 10,000 meters with a howitzer, which is to correct for non-standard conditions. What the software gives you is what we call "should hit" data. If your ballistics software says you should have 45 MOA elevation adjustment at a 1000 yards, that is what you "should hit" with. You dial that in your scope and pull the trigger and the bullet lands in the dirt in front of the target, the impact is your "did hit" data. Your "should hit" data from the software couldn't tell you that the temp outside as you are firing is 20 degrees hotter, you are at 4000 ft, the barometric pressure is lower etc. Basically it can tell you what your bullet would do in a perfect world, but not the one in which you are currently shooting. That is why you have to get out there and gather your own data. When you get this data (scope elevation, cold bore etc.) RECORD that data in a book. It will help you out tremedously in the future shooting that rifle, scope bullet combination at those distances. Besides getting out and actually shooting your rifle at that range, there are a few other things that you can do to help yourself improve at that range. Your rifle, scope, bullet, powder, case etc are all variable in the "equation" that you are using to solve the "hitting the 1000 yards target" equation. Anytime you change one, you need to record data for future reference. I cannot say that enough. If you buy factory ammo, buy as much of one lot as you can afford. When you go to buy more at the same store, loot at the lot numbers. When the lot numbers change, expect that same round that you have used before, to behave slightly differently when shooting it. That is one of several reasons manufacturers have lot numbers. If you hand-load, the powder, primer, case, and bullet are all variables, if one changes, then you can expect changes to bullet impact. They may be slight, but the are there. RECORD those changes in your data book. If you used Varget before and now you are using IMR 4064, but you run out of IMR 4064 but have Varget lying around (assuming the powder lot numbers are the same), you have a much better idea of what down range performance to expect when you load that round. Your data book can be a full blown sniper data book, to a spiral notebook at Wal-Mart. Just record your scope elevation setting for each range with a given load, temperature, wind conditions, etc. You should have it with you every time you shoot. As far as the Coriolis effect, my TFT, there is an entire table for each charge devoted to the rotation of the earth. For each charge of powder, there are 11 tables that you can extract data from to manually compute the trajectory and deviations from standard conditions of each round. Table I is the table devoted to the rotation of the earth. From the equator, which is 0 degrees latitude to 70 degrees latitude either north or south of the equator are listed values for the earths rotation. The further away from the equator you get, the more pronounced the effect of the rotation of the earth is on projectiles in flight. In artillery terms, it is measured in milliradians. There are 360 degrees in a circle. For artillery work, that is not quite accurate enough to use for computing ballistic solutions, so we use mils to get a bit more precise. There are 6400 mils in a circle (real number is about 6283). each 1 degree equals 17.7 mils For 1000 meters on the lowest powder charge settings of 1 Green Bag, 3 White bag, and 1 L (MACS charge), greatest compensation for both northern and southern hemispheres at 70 degrees latitude respectively is 0.3 mils at 1000 meters. And those projectiles are moving really slow, which means greater rotational effect on them vs a rifle bullet since it is moving 3 times as fast as the projectile. That equals a deviation at 1000 yards in Anchorage, AK or somewhere in the ocean between the tip of Chile and Antarctica ( you have other serious problems like cold ocean if you are shooting at 70 degrees south latitude anyway!) is so small at those extreme latitudes (about 8 inches) that the effect in the continental US at 1000 yards is not even worth trying to do the math, but it equals about 3 1/2 inches at 1000 yards. Keep in mind that these final figures were done with slow moving artillery projectiles at about 700 fps. Your .308 is moving about 2750 fps, so the rotation of the earth has much less effect on the .308 bullet than on the projectile. The closer you get to the equator, the less effect it has. In other words, no discernible impact at 1000 yards. |
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Far Beyond Driven
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8shots
Optics Jedi Knight Lord Of The Flies Joined: March/14/2007 Location: South Africa Status: Offline Points: 6253 |
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Griffin, thanks for your very detailed explanation, which I am sure most of us has found useful.
Just on a side note, you say that certain factors have a small impact on accuracy (say 8 inches or 1,5 inches). In rifle accuracy terms these are not small though. OK 1,5 inches are, but certainly 8 inches are not, as the targets are rather small. A bullet has to hit a small vital area for a kill, an artillery shell just needs to fall close to the target (probably within 25 yds or so.)
Shooter seems to be concerned about messing up. A lot depends on your attitude and competency. Can you hold MOA at 100 yds and 300yds and if not have you informed your shooting party so that they can assist you? Are you expecting to make a first shot hit or are you happy to go out there and have fun and learn? We all have to/ had to stand on the 1000 yd mark for the first time.
At the end of the day, go out there, shoot away, have some fun. Keep things safe and no harm is done. If you want to move up to the first shot hits at 1000 yds, well then you need to get out there and put some 1000 rounds downrange at 1000 yds and then start asking questions. Edited by 8shots - February/16/2011 at 01:13 |
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shooter4
Optics Apprentice Joined: February/11/2009 Status: Offline Points: 177 |
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Gentlemen. I got the answers I was looking for. Thankx.
And of course Im gona take this offer and try out a proper 1000yds range. Why not? Yes yes I better master the 500yds first I know. Im comfortable up to 400yds right now but this is a great offer Ill take. Worst case scenario I wont hit the paper at all (I expect so), but at least Im having some fun and watching the others.
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Dale Clifford
Optics Jedi Knight Joined: July/04/2004 Location: United States Status: Offline Points: 5087 |
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right hand barrels have spin drift to the right. Here is a post that shows some of the effects of canting the reticule, and some other topics that may shed some light on your question.
usually right spin drift is amplified by right hand shooters pulling the shot to the right, which is more pronounced when shooting prone than off a bench, and also how much you free recoil you allow in the shot. http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2189771#Post2189771 |
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Griffin99
Optics Apprentice Joined: September/19/2005 Location: Lawton, OK Status: Offline Points: 83 |
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8 shots, just to clarify a bit, what that mean to say is that the 1.5 - 2.0 inches of the earths rotation can't be compensated for at 1000 yards with most scopes out there. The vast majority are either 1/4 inch, 1/4 MOA, or .10 mils (1 mil = 3.6 inches at 100 yards, so .10 = .36 inches at 100 yds). If your scope is adjusting roughly 1/4 MOA for windage at 1000 yards, you would have roughly 2.5 or so inches of adjustment for each click. With somewhere around 1.5 inches of the earths rotation, you can't adjust adjust for it. That was my only point. That is why military snipers shooting 7.62 rifles are not taught to correct for the rotation of the earth in sniper school. They know it has an effect, but can't correct for it, so just a bit of info, especially since the Army's M3A scopes, by spec are 1 MOA elevation adjustments and 1/2 MOA windage. Can't comment on the Marines, but I would say at best, their windage adjustments wouldn't be less than 1/4 MOA, so again, just can't adjust it out. I hope that clarifies my comments about the earth's rotational effect on ranges 1000 yards or less. I don't mean to say it isn't there, just to say it is so small with the equipment (scopes) we generally use, it won't allow us to correct for it, that's all. |
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Far Beyond Driven
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jonoMT
Optics Master Extraordinaire Joined: November/13/2008 Location: Montana Status: Offline Points: 4853 |
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I appreciated the comparison to artillery firing. Interesting background on that.
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Reaction time is a factor...
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3_tens
Optics Jedi Master Joined: January/08/2007 Location: Oklahoma Status: Offline Points: 7853 |
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shooter4 I applaud your attitude. Having fun is the best part. Never forget to laugh .... even if it is at yourself. Thats when it is the most fun. Just wish I could join you. I have never attempted the 1000 yd shot myself.
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Folks ain't got a sense of humor no more. They don't laugh they just get sore.
Need to follow the rules. Just hard to determine which set of rules to follow Now the rules have changed again. |
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Ernie Bishop
Optics Professional Joined: January/26/2010 Location: Gillette, WY Status: Offline Points: 765 |
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Glad you are going to shoot at 1K.
There should be some guys there who will be able to help do what you need to do to have some success. Most of the 1K BR shooters will be happy to help you. Have an open mind to learning and have a great time. |
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Ernie
"If you think you are perfect, just try walking on water." |
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cruft
Optics Apprentice Joined: November/20/2005 Status: Offline Points: 88 |
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make this a "stickey".
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helo18
Optics Jedi Knight Joined: December/02/2006 Location: Montana Status: Offline Points: 5620 |
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+1. My dad used to do artillery in the guards. He would come home and tell stories about it. When I was in OCS we could here the artillery guys practicing all the time. Thanks for that write up and comparison.
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Urimaginaryfrnd
MODERATOR Resident Redneck Joined: June/20/2005 Location: Iowa Status: Offline Points: 14964 |
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Thats why I love shooting at a log in a pond - instant feedback on where the bullet went.
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"Always do the right thing, just because it is the right thing to do". Bobby Paul Doherty Texas Ranger |
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