Reply To: .22 vs .25 in a different way (same weight)
I wish Harry would read this, and comment.
The BC is the controlling factor in retained FPS. While spin rate is important, it pays to remember that pellets are both spin and drag stabilized. The spin rate of any projectile doesn’t slow down very much over its flight time, but can nonetheless effect the stability of the projectile. Poor stability can cause the projectile to wobble (and/or nutate) which reduces accuracy and the effective BC.
As a side light… a decade or so ago, Sierra did some measurements on the varmint bullets to see what the reduction in spin rates were. In the case of a 22-250, the initial spin rate was 240,000 RPM. At 100 yards, the spin rate was still over 230,000 RPM.