Acceptable Zero for new RPR in 6.5
- Thread starter waegeek
- Start date
I can only tell you what my 55 years of field shooting experiences have taught me.
As the range increases the bullet will drift left or right depending on twist. As the range increases the variables such as eddy currents in the wind, angle to target and the animal moving multiply exponentially.
I must smell awful because even at extended ranges with the wind on my side game animals tend to only give me a very short time to range, aquire and fire. The concept of spotting, ranging, adjusting the sights and acquiring again seems to not work for me.
Whether I use a scope or iron sights I zero at 300 yards. I then practice at various ranges to see where that 300 yard zero hits in terms of elevation, if the range gets long, 500 plus yards and if the wind does not act to harshly all my rifles drift right.
In the field I range, aquire, never adjusting sights. Also having a decent range finder and working an area where you have previously ranged helps.
PRACTICE, PRACTICE, PRACTICE!
As the range increases the bullet will drift left or right depending on twist. As the range increases the variables such as eddy currents in the wind, angle to target and the animal moving multiply exponentially.
I must smell awful because even at extended ranges with the wind on my side game animals tend to only give me a very short time to range, aquire and fire. The concept of spotting, ranging, adjusting the sights and acquiring again seems to not work for me.
Whether I use a scope or iron sights I zero at 300 yards. I then practice at various ranges to see where that 300 yard zero hits in terms of elevation, if the range gets long, 500 plus yards and if the wind does not act to harshly all my rifles drift right.
In the field I range, aquire, never adjusting sights. Also having a decent range finder and working an area where you have previously ranged helps.
PRACTICE, PRACTICE, PRACTICE!
I certainly agree with your second sentence, but if I have a bullet "drifting" one direction or the other as the range increases, I know I do not have my reticle pointed at the exact center of my bore. Time to get the tall target and plumb-bob out.
From 300 to 1000 yards using a right hand twist i usually need about a minute of left to get me close.
I keep it centered at 300 and play the shots as the situation allows. I wish one time to get a dumb animal that would give me 15 or 20 seconds seconds to get on them.
SSL
Gold $$ Contributor
If you golf, you know that a 'slice' for a right handed player drifts to the right, the direction of the spin imparted by the miss-struck ball. The same happens to a bullet's flight, but is at a constant rate and occurs farther out due to the speed of the bullet. 300 yards or so is also what I find with the majority of my rifles.
SSL
Gold $$ Contributor
Of course. I was referring to the basic mechanics of the shot without outside influences. Add in wind and other elements and it is indeed a whole new ball game!
Yup it's spin drift. Part of the external ballistics in long range shooting.
Lapua Ballistics tips: Spin drift adjustment
Spin drift (or gyroscopic drift) causes the bullet to drift slightly horizontally at long shooting distances. The direction of the drift is the same as the barrel twist rotation, i.e.
Yes, and I used to throw curveballs, too, but the resistance of a slick bullet ratio to its momentum, compared to a dimpled golf ball, is nothing.
Maybe some bullets do demonstrate "spin-drift," I just never see it with my bullets. The other night I caught a zero-wind relay at 600 yds. Dialed my scope up 12 moa from my 100-yd zero and shot (no windage correction). The straightness of my reticle had been previously verified with a "tall target test" at 100 yds. Where is the "spin-drift error" with my 130-gr. 6.5mm bullets from 100 to 600 yards?
jelenko
Gold $$ Contributor
From JBM Ballistics spin drift calculator - using a Sierra 77 gr SMK, 2800 fps, 0 ft altitude, 8 right twist barrel with wind speed - 0.
| (yd) | (in) | (MOA) | (in) | (MOA) | (ft/s) | (none) | (ft•lbs) | (s) | (in) | (MOA) |
|---|---|---|---|---|---|---|---|---|---|---|
| Range | Drop | Drop | Windage | Windage | Velocity | Mach | Energy | Time | Lead | Lead |
| 0 | -1.5 | *** | 0.0 | *** | 2808.3 | 2.515 | 1348.2 | 0.000 | 0.0 | *** |
| 100 | -0.0 | -0.0 | 0.1 | 0.1 | 2565.3 | 2.298 | 1124.9 | 0.112 | 19.7 | 18.8 |
| 200 | -3.8 | -1.8 | 0.3 | 0.1 | 2334.1 | 2.091 | 931.3 | 0.234 | 41.3 | 19.7 |
| 300 | -14.0 | -4.5 | 0.6 | 0.2 | 2115.6 | 1.895 | 765.1 | 0.369 | 65.0 | 20.7 |
| 400 | -32.0 | -7.6 | 1.1 | 0.3 | 1909.1 | 1.710 | 623.1 | 0.519 | 91.3 | 21.8 |
| 500 | -59.6 | -11.4 | 1.8 | 0.4 | 1713.0 | 1.534 | 501.6 | 0.685 | 120.5 | 23.0 |
| 600 | -99.1 | -15.8 | 2.9 | 0.5 | 1526.0 | 1.367 | 398.1 | 0.870 | 153.1 | 24.4 |
| 700 | -153.6 | -20.9 | 4.2 | 0.6 | 1348.7 | 1.208 | 310.9 | 1.079 | 189.9 | 25.9 |
| 800 | -227.3 | -27.1 | 6.1 | 0.7 | 1183.5 | 1.060 | 239.4 | 1.317 | 231.8 | 27.7 |
| 900 | -325.9 | -34.6 | 8.6 | 0.9 | 1060.0 | 0.949 | 192.1 | 1.587 | 279.2 | 29.6 |
| 1000 | -455.3 | -43.5 | 11.7 | 1.1 | 1003.3 | 0.899 | 172.1 | 1.878 | 330.6 | 31.6 |
And who the hell is "JBM Ballistics?" Their website smacks of some nerd in his mother's basement who has never, or only very rarely, actually fired a rifle (kinda like some of the people who have frequented this thread). I have no idea where this nerd got his "data." Did he fire a single round coming up with his charts, or just lift the data from some other nerd in some other mother's basement?
Excuse me if I continue to base my "ballistics concerns" on what I actually see happening on my targets.
Moreover, .5 moa at 600 yards is in most cases going to be trumped by the air movements. It is not something worth even thinking about, if it exists at all, not to mention that few people have a rifle that shoots accurately enough at 600 yards to even be able to discern that they are .5 moa off to the right or left.
BUT, that said, I have felt cheated that none of my bullets experience it, and I will be happy to acknowledge its existence just as soon as it shows up on an actual target.
CharlieNC
Gold $$ Contributor
Who is JBM? Just one of the oldest and most widely used ballistic resources in the world. Read any book or authoritative article about ballistics and you will find spin drift is a fundamental accepted physical principle, not a big deal at 600yd but very important at longer ranges such as 1000yd which is quite obvious in the chart just above. And at these longer distances it affects vertical as well to the tune of 10% or more of the wind value, which some updated apps provide the option to include. When shooting steel matches from 400-1200 yards I find it useful to set my turret 0.2mil left to account for spin drift in order to use the reticle for windage alone.
jelenko
Gold $$ Contributor
What CharlieNC did was convince me he doesn't have the foggiest clue who "JBM Ballistics" is.
And, yeah, I only shoot 3 or 4 days a week. This was the steel I shot at 1,000 yards today, no cross-breeze at all. Come up from my 100-yd zero was 29.0 moa, adjustment to windage was ZERO.
WHERE IS THE "SPIN DRIFT?"
Oh wait, I know, I have to get out to 2,000 yards to see it, right?
Most people shooting at 600 yds and farther would be much better off forgetting about "spin drift" and instead concerning themselves with whether their scope is on straight.
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CharlieNC
Gold $$ Contributor
I don't know Bryan Litz either, but I did read his book. Maybe try sleeping in a Holiday Inn Express with his book under the pillow!What CharlieNC did was convince me he doesn't have the foggiest clue who "JBM Ballistics" is.
And, yeah, I only shoot 3 or 4 days a week. This was the steel I shot at 1,000 yards today, no cross-breeze at all. Come up from my 100-yd zero was 29.0 moa, adjustment to windage was ZERO.
WHERE IS THE "SPIN DRIFT?"
Oh wait, I know, I have to get out to 2,000 yards to see it, right?
Most people shooting at 600 yds and farther would be much better off forgetting about "spin drift" and instead concerning themselves with whether their scope is on straight.
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