RPM relating to stability & or accuracy

Bullet RPM

http://www.bergerbullets.com/twist-rate-calculator/ and bullet length- http://www.jbmballistics.com/ballistics/lengths/lengths.shtml Bullet length matters in my 243 winchesters. 1-10 twist is not super accurate with 100 gr + bullets, but mostly using the 18 inch barrel. The 27 1/2" barrel does better. More RPM'S I guess?

Calculating Bullet RPM — Spin Rates and Stability

For the most part I really don't bother with calculating spin rate. I focus more on the bullet verses the load and how the bullets deliver using or working up loads. That said the above link has some data on the subject.

Ron

<EDIT> I see 243Winxb is up and about his morning. </EDIT>

243winxb said:

Bullet length matters in my 243 winchesters. 1-10 twist is not super accurate with 100 gr + bullets, but mostly using the 18 inch barrel. The 27 1/2" barrel does better. More RPM'S I guess?

Click to expand...

It is probably the velocity due the longer barrel.

There's also a JBM twist rate calculator that I've personally found more useful, http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi I'm not an expert but the faster you push within limits seems to accelerate rpm, a marginally stable bullet at 2600 rates better at 2900 fps, this doesn't guarantee accuracy but the concept is simple enough.

Here's one example of bullet spin rate decay; a Sierra 30 caliber 175 HPMK spinning at 160,000 rpm leaving the muzzle. Used Geoffery Kolbe's formulas:

Bart, thanks for sharing the Excel data.

Ron