[ARCHIVED THREAD] - spin drift chart m855

Posted: 8/24/2011 3:09:46 PM EDT

I have a 1-7", 20 in barrel and I would like to know what the spin drift is from 300-800 meters, with m855 ammo, please

Posted: 8/24/2011 3:11:17 PM EDT

[#1]

bump for the info

Posted: 8/24/2011 3:42:38 PM EDT

[#2]

Quoted:

I have a 1-7", 20 in barrel and I would like to know what the spin drift is from 300-800 meters, with m855 ammo, please

Applied Ballistics for Long Range Shooting, by Bryan Litz, gives the formula for the Gyroscopic (spin) drift as:

Drift = 1.25(Sg+1.2)tof^1.83

Sg = Gyroscope stability factor

tof = time of flight

Excel Spreadsheet Format: Drift=1.25(Sg+1.2)*tof^1.83

Plug and play.

Posted: 8/24/2011 3:49:53 PM EDT

[#3]

I haven't seen anywhere where time of flight has been converted to distance. Please explain this more if you can.

Posted: 8/24/2011 4:05:01 PM EDT

[#4]

This is for Sierra 69s. Not quite the same, but the same bullet length.

Range Drift
Yards (MOA)

100––- 0.1
200––- 0.2
300––- 0.2
400––- 0.3
500––- 0.5
600––- 0.6
700––- 0.8
800––- 1.0

Posted: 8/24/2011 4:05:36 PM EDT

[#5]

Quoted:

I haven't seen anywhere where time of flight has been converted to distance. Please explain this more if you can.

This is available online, but I will post it for you.

Range  ToF
0      0.00
100    0.11
200    0.24
300    0.39
400    0.55
500    0.74
600    0.96
700    1.21
800    1.50

Sg is dependent on atmospheric conditions.
At sea level, with std. temp and std. pressure, the M-855, fired out of a 20" barrel with a 1/7" twist, has a Sg of 2.5

Posted: 8/25/2011 5:59:43 AM EDT

[#6]

Quoted:

I have a 1-7", 20 in barrel and I would like to know what the spin drift is from 300-800 meters, with m855 ammo, please

300M - 0.8"

400M - 1.5"

500M - 2.7"

600M - 4.3"

700M - 6.6"

800M - 9.7"

Posted: 8/25/2011 6:11:14 AM EDT

[#7]

Spin drift doesn't play a big enough factor to try and compensate for it. Especially if you are shooting ball ammo.

Posted: 8/25/2011 7:56:40 AM EDT

[#8]

Topic Moved

Posted: 8/25/2011 9:59:20 AM EDT

[#9]

Thanks everyone!

[ARCHIVED THREAD] - spin drift chart m855

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[ARCHIVED THREAD] - spin drift chart m855

[ARCHIVED THREAD] - spin drift chart m855