With a sport PCP (like the M-rod) so far I have NOT lost energy with heavy weights….normally gain a little energy.
Velocity is lower as the weight goes up, but not low enough not to earn more energy than the lighter pellets.
Typical would be:(in this case all JSB pellets)
8.4gr. / 1034fps / 19.9 foot pounds
10.3gr. / 974fps / 21.7 foot pounds
13.4gr. / 897 fps / 23.9 foot pounds
16.2gr. / 834fps / 25.2 foot pounds
(power guys: this was was not that rifle's max.)
Do have some match rifles that don’t follow those rules… with really limited air use and low speeds with lite weight pellets to start with, will often show less energy with the heavy weights.
Do get odd ball results from pellets that fit tight or have a lot more bearing area...the 16.1 EunJins will be a bit slower than the 16.2 JSB’s.
Shot count hasn’t been too far apart…..if running efficiency calculators, often the heavy weight ends up a little more efficient (it’s air use vs energy, so the little gain in energy off sets a small change in shot count).
Normally the heavier pellets have a higher BC. That doesn't make up so much trajectory (gravity, but does gain wind-age resistance and even better retained energy.
Basically you get more hold over, but less wind hold off.