Something to consider on the subject: Power factor is essentially momentum... pf=mv Kinetic energy=mv^2 Therefor, a 115 grain bullet making 120 pf carries more kinetic energy than a 147 grain making the same power factor. So the question becomes, does a transfer in kinetic energy cause the popper to fall or does a transfer in momentum cause the popper to fall. Personally, I think the heavier the bullet, the safer you are making it to fall when it should.