Originally Posted by Joe King
What I would like to know is how am I stabilizing a 53gr vmax in my 22-250 with a 1 in 14 twist. It shouldn't work but it does. according to a twist rate calculator I would have to push it north of 4100fps. All I got is my gunsmith is really damned good, and my dies are make some very concentric loads, so everything lines up just so.
a long (and I mean a really long time ago) ago Walt Berger told me that it took 179K rpm to stabalize his VLD's at impact. We all thought hey that's right, and it did make some sense at the time. Later we learn that some other things (the data was there already, but nobody bothered to listen). But this also answered a lot of questions as to why I couldn't get 88LD's to stablize in a 6mm that was really spinning the bullets extremely fast. I was roughly one twist in a foot too slow.
Now as to how you are doing a .29 B/C in a 1:14 twist is a mystery. Shouldn't be able to do this, and it's been proven out many times over the last 12 to 14 months. Have you actually measured your twist rate? Or simply went by what you were told. (I've seen them vary as much as an inch). In a 12 twist the .29 is right there, and with a factor of .85 it's still close. I've found that the 55 grain Vmax is about it with a 1:14 twist, and a 50 grain Vmax works better. But on the otherhand a 55 grain Nosler BT has a slightly lower B/C than the Hornaday, and may well work. I can shoot the 60 grain BT's just fine in a 12 twist due to their lower B/C number. Never had a 1:12 twist .223 to compair notes with, but have been around several 1:14 twist 22-250's and the results are always similar
Reason I use the factor number is to allow for friction and other varibles. You figure take the bullet length and divide the diameter into it, and then divide the twist rate into that number. Then I multiply it by .85.
example: .88 length divided by .223 equales 3.946. Then divide that by the twist rate of 12 for .328. That would be for perfect conditions. Now I mulitply that by .85 for .279B/C. Some guys use .80 and some use as high as .95 for a factor number. A .90 factor number gives you a near perfect match for the 53 grain Vmax with a .29B/C (note I'm only guess at the actual length). Is the formula perfect? I can't say but it works. I have noticed that the larger the diameter of the bullet the lower the factor number is needed (for me anyway), but the .85 number is just a generic number I use. I never get lower than .80 and have gotten as high as .95 in the past