115 vs 125 vs 135 vs 145 for steel

[SPQR476]

If you want to geek out, what we are really talking about is an application of Force to the steel, so you can play with mv/t, but there's a torque component based on distance from the axis of rotation in the case of a popper, etc., blah.

I think that in reality, the imperfect nature of the energy transfer means that the math is only useful in being predictive when talking about changing a single variable, e.g., bullets of same weight, same construction, with a velocity difference, and not always.

I believe that if a guy wanted to really hash this out, it would take a high speed camera with a 90 degree view of the impact face, with a perfectly controlled impact point on a perfectly smooth popper face and a graduated background to determine the movement and velocity imparted to the popper.

Having watched a few impacts on high speed, I think we'd find that even at identical momentums, bullet weight is a factor, but I'd bet that bullet construction and shape are, too, and it all relates to how much of that momentum gets truly transferred to the steel, and how much is lost radially from the impact point as the bullet breaks up. It also might prove out that the heavier bullets are transferring more force to the plate in part because the greater sectional density and slower velocity means that bullet fragmentation happens over a longer time, and that a more solidly constructed bullet (fmj) might transfer more force to the plate as the force required to fragment the bullet would be higher , keeping the bullet intact a few microseconds longer to allow for more transfer of energy, and when talking about steel, HP may actually transfer less energy since they come apart easier.

This is just theory-- I'm not pretending that this is the definitive answer. I just think that the dynamics of the impact and energy transfer have a lot to do with various bullet performance on steel, and it might be worth setting something up to look at it.

[Yeti]

Interesting discussion.

Most folks always thought that a heavier FN bullet was better, but it all depends on what YOU can shoot accurately, quickly.

WOW I guess I will just stick with 125s and not worry about it.

For us mere mortals, I think RC has it covered. Pick a load that works for you and practice, practice, practice.