“While I applaud the efforts of Canada’s NFA to put out these sources, I think Peter Chronhelm needs to tweak things a little, especially on the bullet stability calculator (excel). If you plug in a bullet like a 6mm Berger 105 VLD bullet going 2800 fps, the calculator says the stability factor is not nearly adequate with a 1:8″ twist barrel, meaning the bullet would not even be stable shooting it out of a 1:8″ twist barrel. This also is the case with a 115 gr 6mm out of a 7.5″ twist barrel, but anyone who shoots 6mm’s knows that a 1:8″ twist will fully and adequately stabilize a 105-108 gr 6mm bullet and the 115’s are all well stabilized by a 7.5″ twist barrel.

I don’t want to “pour cold water” on what Peter has done, but it’s no good to put something out there that does not give accurate information and results and winds up misleading people.

Maybe I just don’t know how to use the calculator, but I am pretty sure I was using it correctly.”

Robert Whitley

EDITOR: Robert Whitley makes some very good point. Testing his example, we ran the Berger 105s through the calculator at 2800 fps and came up with a stability factor of 1.0, listed as marginally stable. The recommended stability factor is 1.3 or greater. It could be the model doesn’t work particularly well with VLD-style bullets which tend to be longer for their weight. Bullet length is one of the key variables in that Excel calculation.