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so I was trying to find a manual calculation I could do to work out spin drift and the JBM site came up on Google, anyway when you're on that trajectory page and write in all the crap there is the first part at the top where you choose your projectile. I went down until I found 168 Amax I saw the moly coat one under it too but under that there is the Litz. Whats the Litz one about?
Also if anyone could link me to a site or tell me the way to manually work out spin drift that'd be great.
Brian Litz BC's are arguably the most accurate as he has tested them or worked them out from the design.
I wouldn't get hung up on spin drift unless you shoot past 650 heaps and its always around 1.5 - 2" within reason.
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So its the same projectile not coated or anything like the other one is just going off his bc for it? Also does the moly coating add noticeable weight to the projectile?
The Litz BCs are measured by Bryan Litz (ballistician at Berger) with doppler radar from memory and are often more accurate than estimated numbers from the manufacturers
Yup to Litz and no to moly adding weight that matters.Quote:
Originally Posted by Toby
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All right that solves that, anything about manually working out spin drift?
There's a calculator on the JBM site that does it.
I found how it does it for me. Is there some way it shows me the formula?
There is no simple way. Either use the JBM calculator, or just log everything and try work out what it is from your log, if it even shows up in your results.
Ohk, that's a bugger. I was hoping it'd be something like finding the sd where you can take this number and times it by what not and so on to come out with the result.
It's not a real simple thing to work out. The calculator is a "best guess". It's also super hard to measure.
Does it make a difference within 1000yrds? the spin drift that is.
Sometimes. It really is an insignificant value until 600m+
5cm at 500 meters? meh.
Oh hell that's more then I was thinking. Thanks gimp
Determine the gyro stability factor (SG) of your bullets and firearm. Ask for this information when you purchase bullets. If the vendor does not know, there is a calculator that can help determine the SG.
Calculate drift with the following formula: drift = 1.25 x (SG + 1.2) x TOF ^ 1.83. Start by raising your time of flight to the power of 1.83. In the example, 1.9 raised to the power of 1.83 is 3.237. If the SG of our bullet and gun is 1.4, then the equation becomes: drift = 1.25 x (1.4 +1.2) x 3.237 for a result of 10.52. This means in this example, the bullet will drift 10.52 inches to the left or right depending on which twist the gun barrel has.
Found this.
Dialing in .250 moa left for 500 yrds and .5 moa left for 1000 yrds will negate 90% of the right hand drift effect of spin drift at those distances.
The total effect of spin drift is a combined effort of a few factors including but not restricted to projectile length, surface area, rpm and air density, the total amount of spin drift experienced often being as variable as the various projectiles used.
Coriolis has a 4 directional effect on your projectiles point of impact depending on your projectiles flight path in relation to the earths rotation and in certain situations can cancel out the effects of spin drift, and in others exaggerate it.
And just to make matters even more interesting on the day the wind currents, eddies and subtle breezes you experience at your private range can often affect your shot more than either of these two conditions.
dosnt shooter eliminate this carryon?,(the need to get the cryon out)
Yes, as can most ballistic calculators
with the longer calculation's dose shooter tell you it has compensated for it or you assume its been done or is it in the advanced version setting???
Thanks 7mmsaum
Its a capability that you activate in your apps settings section.Quote:
Originally Posted by Neckshot
Toby, if you're interested in some high-end physics, read about precessional force / Magnus effect. It is about what happens to spin stabilised projectiles when they experience wind from the left or right...
Search for an article on Wind Shooting by Ross Mason, he has a neat way of explaining it.
trivia, the pommies made their 303 in left & right handed rifling, the reason for this from what I'm to understand was the effect of coriolis. And the direction that they would be firing. Someone may be able to expand on this?
Cheers Rob
Quote:
Originally Posted by 7mmsaum
That just made me think, if you have a right hand twist and wind is blowing in from the right does that mean it'll drift less then if the wind was to blow in from the left. Also when the wind comes in from the left and pushes the projectile does it spinning in the direction of the wind help it move even further?Quote:
Originally Posted by ebf
but what range are you shooting at?Quote:
Originally Posted by Toby
<300yds no worries, I'd suggest your ability to shoot is the biggest thing.
If you are shooting at 1000 yds and just have to get a 1st round hit then its a calc job. If however you have some wind and a changing angle that will be your biggest effect and the hardest unknown...it could be 3 MOA, 8 MOA or whatever and changing. Then if the furry thing is moving its 1.75 seconds to impact at that range so you have to lead as well. Personally I'd never shoot a furry thing at that range because I would consider I couldnt guarantee an ethical / clean shot.
I don't shoot at any range but am interested in the effects of spin drift and so on.
It will also clime up or down a cross wind.
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Yeah I read that in the thing ebf told me to check out
Same reason a soccer ball or baseball curves!