I had an excellent conversation with Paul at Sierra, about minimum bullet RPM and bullet stability, we zeroed in on they 107gr HPBT, and he was telling me that the minimum bullet RPM, that he has sent down range and still maintain stability, is 216000 RPM he achieved that from a 6 BR that he sent at 2400 FPS from an 8 twist barrel, Then I asked him about slower twists and if it would be possible to stabilize the same bullet, I told him about my other chamberings and so he proceeded to tell me if I maintained that min RPM it would stabilize, so we did some math and this is what we came up with, the formula is muzzle velocity X 720 ÷ barrel twist, remember 216000 RPM is the magic number, I have came about these findings myself on my own, but it was nice to hear it from the bullet MFG, I have found the number is even lower closer to 200000 when you start to get past the 3500 FPS mark, but I will stick with 216000 for the sake of argument.

2400FPS for a 8 twist barrel 6BR check

3000FPS for a 10 twist 243 AI check

3600FPS for a 12 twist 6mm06AI check

4200FPS for a 14 twist 6mmMachIV there is load data available to achieve this.

Dean