Originally Posted by MontanaRifleman
Using 5000' elevation and 40* in Paradise Valley yesterday, the Berger twist/stability calculator shows the 160 Matrix SF was 1.45 @ 3100 fps and the 140 VLD (Match Target?) was 1.49 @ 3300 fps (guessing) out of your 9 twist 264 WM.
I would guess your 140's are on the edge of stability in the 9 twist.
Yah, lol.. I used that same calculator while waiting for my 160's to come in the mail. My numbers are 1975 elevation, and actually shoot the 140 Hunting vld's. Using those numbers and a 9 twist (@ 3135/140vld) I was getting 1.3-ish stability. With the 140's. If I recall off the top of my head, about 1.16 or 1.2-ish for the 160's.. crossed my fingers hoping that's be close enuf, but no sir... I also plugged in a bunch of numbers out of some bench-rest articles using velocities, twists & bullets they were shooting thru 6.5x284's and noted that the 8.5 twists (and their load info) was giving stability numbers on that calculator also in the 1.3 range* ..would think those boys would have good reason using 8.5 and 1.3 stability numbers to shoot 1000y matches. Compares nicely to my 140 numbers thru my 1:9.. obviously tho, not so nicely with the 160's. And my targets prove the fact*
Interesting either way* Definitely need more than 1:9 in this case for the 160's.. that info should help "some guys" anyway!