Upgrades avenge x .25

I've also been doing some looking into the power plenum for the Avenge-X.
As I understand it the concept of a larger plenum provides potential for tuning to a lower regulated pressure with less hammer spring, resulting in the same FPS for a given pellet. I'm a newbie to this sport but I gather that decreased hammer spring also means cocking effort is less, making things smoother to stay on target between shots. There is also the claim of increased regulated shots for the same given pellet or slug shooting to the same distance. Additionally, there is a forum in the UK with a claim to a calculator, although I have not yet been successful in recreating the math in my own spreadsheet. His calc for the energy stared in 1cc of compressed air @22 degC @Reservoir max pressure has stumped me.

https://airgunforums.co.uk/threads/...retical maximum out,Shaggy and 1 other person

I found 3 power plenums on the market:
One from SA Air (https://saairrifles.co.za/product-tag/air-venturi-avenge-x-plenum/)
One from an ebay seller (https://www.ebay.com/itm/405549486165)
A couple from another ebay seller (https://www.ebay.com/str/alienairgunsandbargains)
Then there is this video from Badger Air Sport, ()