twist rate stability calculater

[n zeder]

have ordered a 1/12 twist barrel for my 22 dasher with 53gr vmax in mind for rabbits out to 500mtr+
ran the berger stability calculater for that combo and its only just stable,it recommends 10 or less which surprised me.wondering if i need to change twist rate,my gunsmith said 12 twist was standard for the lighter bullets and thinks i should stick with 1/12.
my 1/10 .204 ruger shooting 40gr was also deemed marginallystable??thats a very accurate rig...how reliable is this calculater?

 

[Laurie]

You'll be fine with 1 in 12". There are two issues here that overstate the spin rate and hence rifling twist pitch needed - first, the light acetate tip on the VMax and AMAX models extends the bullet overall length (which in relation to calibre is what mostly dictates the required spin for full stability), but doesn't actually affect is as much as if the metal bits (jacket and core) went as far forward ... and secondly, the Miller Rules Formulae which the Berger calculator uses is designed for boat-tail form bullets. The boat-tails on a lot of light 224 bullets are pretty vestigial and a far cry from what you find on say a 6.5 or 7mm Hybrid. They're closer to a flat base than a 'real' boat-tail. FB bullets use quite different stability criteria (see note on the Berger twist calculator web-page) generally needing a full inch less twist than a typical true boat-tail, sometimes more. Tens of thousands of 222 and 223 Rem shooters have used this bullet for years with good results in slow twist barrels.

 

[n zeder]

You'll be fine with 1 in 12". There are two issues here that overstate the spin rate and hence rifling twist pitch needed - first, the light acetate tip on the VMax and AMAX models extends the bullet overall length (which in relation to calibre is what mostly dictates the required spin for full stability), but doesn't actually affect is as much as if the metal bits (jacket and core) went as far forward ... and secondly, the Miller Rules Formulae which the Berger calculator uses is designed for boat-tail form bullets. The boat-tails on a lot of light 224 bullets are pretty vestigial and a far cry from what you find on say a 6.5 or 7mm Hybrid. They're closer to a flat base than a 'real' boat-tail. FB bullets use quite different stability criteria (see note on the Berger twist calculator web-page) generally needing a full inch less twist than a typical true boat-tail, sometimes more. Tens of thousands of 222 and 223 Rem shooters have used this bullet for years with good results in slow twist barrels.

cheers laurie,yes thousands of .22 cal shooters cant be wrong,my thoughts as well.always good to get others thoughts on this as it had me abit worried...
the oal i plugged in was not including the vmax tip btw.