Bullet Stability ??

[WayneS]

This is usually not a concern in competition rifles but I thoiught I'ld ask here, when running stability programs, they call for the OAL of the bullets , BUT I've read somewhere ?? CRS  that in the case of BTHP bullets that the correct measurment should be of the OAL of the lead core ?? that is measure the distance from the tip ot where a pin touch's the core then substace that from the OAL and that measurment is the one to use

[trotterlg]

I think that is just urban mith, some bullets do not even have lead cores.  The wieght/length/Sectional Density all add up to determine if the bullet is stable.  The formulas use generally accurate estimates, you will likely find a bullet to be stable that does not show as stable in the programs.  Also, the bullet spin rate does not decrease as fast as it's velocity does, however the programs do the calculation as if it did.  Larry

[Nobade]

Interesting read on the subject I found last night...

http://riflemansjournal.blogspot.com/2010/06/ballistics-heavy-bullets-in-113-twist.html

[Catfish]

I have seen programs that figure out what twist you need to stablize a bullet but they are so complexed that I don`t mess with them. The simple rule of thum is that in a given caliber, the longer the bullet the faster the twist needed to stablize it. It does not matter if the bullet is lead or solid copper, it`s the lenth that matters.

[helotaxi]

Think about it this way, a short, fat spinning top is stable (relatively) at a certain RPM or faster.  If you were to add a 2 foot long soda straw to the top, perfectly aligned with the axis of rotation, the top will not be stable at the same minimum RPM.  The straw adds negligible weight to the whole ordeal but still plays a big factor in its stability.