Re: Bullets vaporizing in mid-air
PacNor's rule of thumb ain't bad though. Atleast for common heaviest per cal bullets.
I've used it for many years, specifically with Bergers;
Stay this side of 290Krpm with Bergers(ok, old Bergers), and <310Krpm with SMKs, or JLKs. This, in smaller cals.
Krpms = (720*Vel/Tw)/1000
At 2800fps/7tw you're at 288Krpms, and normally bullets hold up fine. But a 6/284 is generating more bore heat than usual..
If you want to see it over and over from every angle, research 22-243 90gr bullets in 7twist. These guys have a very narrow band to work between stability and failure.
With larger bores, or shorter bearing bullets per bore, the limits can be raised upwards of 320Krpms.
So even if their rule doesn't pass all tests, it does indirectly define the energy where failure is a factor. Bore heat, friction,, The energy wasted in spinning up a long bullet, in a bore.
Last edited by Mikecr; 06-17-2009 at 09:21 AM.