I was just rounding up numbers to show that I knew muzzle velocities can be way different to give 12fp with different weight pellets.
Normally ... in pcps you get a higher muzzle energy with heavier pellets and with springers you get a higher muzzle energy with lighter pellets. It's the way the air is delivered. Springer ... shuv a penny, quick initial blast ... so light pellet should be more affected. PCP ... more like someone keep blowing through a straw behind the pellet ... so once you get the momentum going, a heavier pellet should be more efficient.
I was giving an example, that I hoped added weight to Rich's comment, that he thought the pressure of air initially behind a pellet in a springer before it moves is high, by stating that when using Barracudas ( very tight in breech ) in an old Vulcan they gave the best energy.