Some "simple" math...
FSR fins are about 1 rev per 12" of flight.
At 300 fps this means 18,000 rpm, assuming everything is "perfect"
After a discussion with uv_halo, we decided the Lapco is about 1 rev per 48" of flight, which translates to 4,500 rpm
He and I agree that the Hammer Head and the Lapco use about the same rifling rate, so the 1,350 rpm number is either measured or concocted.
I am glad to see that someone has finally figured out that bullet style rifling is not as good at gripping a "soft" shelled round, as pellet gun rifling.