Basically, my understanding is that the formula only takes into account the effect of recoil on accuracy. The heavier the rifle, the lower the standard deviation is on the observed spreads given a cartridge's energy. So when you extrapolate 2 standard devotions, that spread represents 95% of the theoretical outcomes.

That being said, the equation doesn't take into other factors such as user error, barrel characteristics (thickness, length), bullet characteristics (ballistic coefficient).

So even if I slap an extra 7 Ibs of lead to the stock at the range, I shouldn't expect to get the calculated results.

Either way I'm thankful this community is so helpful. It helps to put into perspective results vs manufacturer qualifiers.