Heavy pellets pcp/spring

[Ringokid]

Hi all looking for some tech info, there must be some boffs.
I know heavy pellets are more efficient in pcp vs spring in general but why, what is the science behind it. (Probably a simple answer, maybe)

 

[jesim1]

It’s to do with the way the potential energy in the compressed air is converted to kinetic energy. In a PCP there is a sudden blast of air caused by it expanding rapidly and pushing the pellet along the barrel. In a springer the process is comparatively slower, as the piston compresses the air the pellet starts to move along the barrel and is more of a longer shove than a quick smack.

Heavier pellets are more efficient with the fast expansion as they start to move suddenly and benefit from the quick blasts sudden expansion, whereas the lighter pellets start to move too quickly with that kind of expansion, and so do not allow the pressure to build as highly behind them as they are already moving and creating a larger expansion area behind the pellet as it moves along the barrel. So the light pellet is in fact too light for the design and not as efficient as the heavy one. The reverse is true of heavy pellets in a springer, they are too heavy for that design and therefor less efficient.

Not the most scientific answer, but pretty close to the physics of it

 

[Ringokid]

Thanks that sounds reasonable, never looked at it in that way

 

[JimPlas]

The pellet is propelled by two types of energy. The obvious one is the potential energy associated with the pressure and volume of the air (PV energy), which becomes flow energy as it flows up the barrel. The second is the air's internal energy (U), associated with its temperature. Both types of energy help drive the pellet.

Heavier pellets take longer to travel up the barrel, so are exposed to the two types of energy for longer, and so gain more kinetic energy.

In springers, heavy pellets are too close to the breech at peak cylinder pressure/temperature for maximum energy transfer, and more of the energy is lost to piston bounce.