Doesn't the Air Arms S510 have a shrouded barrel? Isn't the shroud air filled behind the muzzle with a baffle in front of the barrel muzzle? Or is it only the endcap on the shroud that fills the space in the shroud? Either way, I get that a 12 FPE air rifle has less muzzle blast to upset pellets. Especially if the barrel is longer. Certainly, the 30+ FPE versions have air strippers to fill the reflex portion of the shroud.
It's not the powerplant why the HW80 is still accelerating at 16" vs Cardew's rifles using much less. The powerplants between the rifles is different. But not enough to do that. The difference is the barrel.
“You lost me when you started talking about the "tail" of a barrel.”Yep