Here is a question:

Say I have a pellet of 15g (grain). Its velocity is 550 ft per second in my air rifle. Using the calculator on the website below, this produces an energy level of 10.08 ft/lb.

https://www.airgundepot.com/airgun-calculators.html

Simple logic therefore suggests that each 55 ft/second velocity is equivalent to approx 1 ft/lb energy (550 ft sec divided by 10.08 ft/lb). Similarly, 5ft/lb energy would be 275 ft/second velocity (half of 550 ft/sec).

However, neither of these deductions is correct. Type in 55ft/second and the calculator produces a ft/lb energy of merely 0.1 ft/lbs. Type in 275 ft/sec and the calculator says the energy is only 2.52 ft/lbs, when it might have been expected to equate to 5 ft/lbs.

At the other end of the scale, if we raise the energy by merely 11 ft/second from 550 to 561 ft/sec, then the energy rises to nearly 10.5 ft/lbs from 10.08 ft/lbs.

The question is, why does this calculation not work equally; why does it work exponentially as the velocity increases, leading to a much faster rise in the ft/lb rate as the level of velocity rises?

It means that a rise of a few foot per second can significantly raise the ft/lbs rate. Thus, a difference of 11 ft per second velocity between the fastest and slowest pellet might seem well within the parameters of an efficient and consistent spring gun but this will also result in a rise of the ft/lb measure of nearly 0.5 ft/lb.

There is doubtless a simple answer; I wonder if one of the many experts here could kindly explain it.

Regards to all,
Andrew.