hombre243
.30-06
Here is something interesting...but...if this is optimum, why is it not used. (Why a 1/10" twist?)
If one believes this, a 170 grain bullet with a length of 1.022" (Sierra FNSP) requires a twist of 1/13.9". A 125 gr bullet of .725" requires a twist of 1/19.6".
It is the Greenhill Formula: 150 (or 180 for over 2800 fps) (constant) x bullet diameter squared / bullet length.
A 1/10 twist seems a bit fast for anything but a huge 220 gr bullet. I do not have any of those so if someone has a 220 gr .308 bullet and can measure it please post the length here. I am real curious about the twist required.
Here is a calculator that may help see the calculations in action:
http://kwk.us/twist.html
Oh, PS, I cannot believe this calculator is worth much because if it was true to it's word, 3030 barrels would have a twist rate slower than 1/10.
If one believes this, a 170 grain bullet with a length of 1.022" (Sierra FNSP) requires a twist of 1/13.9". A 125 gr bullet of .725" requires a twist of 1/19.6".
It is the Greenhill Formula: 150 (or 180 for over 2800 fps) (constant) x bullet diameter squared / bullet length.
A 1/10 twist seems a bit fast for anything but a huge 220 gr bullet. I do not have any of those so if someone has a 220 gr .308 bullet and can measure it please post the length here. I am real curious about the twist required.
Here is a calculator that may help see the calculations in action:
http://kwk.us/twist.html
Oh, PS, I cannot believe this calculator is worth much because if it was true to it's word, 3030 barrels would have a twist rate slower than 1/10.
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