Thread: Whats the difference

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

Originally Posted by Toby

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?

Yup to Litz and no to moly adding weight that matters.



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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.