This all started because I put a Dream Valve on my .22 Talon with a 19 inch barrel.
Had the regulator set at 200 bar and got 1100FPS and 68FPE
So I decided to figure out the optimal plenum volume.
What I did was calculate the barrel volume and then tried 25CC, 50CC, 125CC and 250CC plenums.
Huben Power Dream Valve Universal: 25CC Plenum
Huben Power Cricket Max-ATH: 50CC Plenum
Shan Bao 20CM 300psi Tube and regulator 1/2 of a Huben: 125CC Plenum
Shan Bao 40CM 300psi Tube and regulator 1/2 of a Huben: 250CC Plenum
This was with AirForce .25 Condor and Talon with 24 inch barrels.
(.125*.125)*3.14*24= 19.31CC
The objective was to find at what point adding more plenum volume reached diminishing returns.
3x or 4x barrel volume seems to be optimal
Sufficient plenum and air path (which the AirForce platform provides) you can accelerate the pellet the length of the barrel.
The 50CC was good little short of 3x
The 125CC pretty much maxed the FPE gains at 6x
The 250CC was virtually identical to the 125CC
Bob Sterne was working with a conventional Poppet style rifle.
Way too many variables in the air path to do anything other than find what a specific rifle can add via plenum
Hammer spring
Hammer weight
Poppet spring
Transfer Port
Poppet Dwell
Air pressure
Plenum port
Right angle air flow changes
I'm sure there are probably others but change any one of those and you change the volume of air through the Poppet. So optimizing the plenum is custom for each poppet rifle.
The Condor firing H&N 30gr Barracuda was getting 880FPS ate 1750psi with the 125CC plenum
Same gun and the 25CC plenum required ~2000psi.
Cranking the regulator to 200bar with the 125CC and the pellet went supersonic.
You can really lower the regulator pressure with a well optimized plenum.
Or you can get some bit time FPE
Unfortunately the Shan Bao tubes are on AliExpress are either out of stock (40CM), with the wrong style regulator (40CM) of big jump in price (20CM). The other issue there is connecting up those tubes to a standard air rifle.
To do that gets a tad heavy and unwieldy. Need a U adapter.
Niksan Ozark .25, Shan Bao 40CM tube, Huben Regulator, Huben U adapter and a 1.6L bottle.
Note the droop on the tube
View attachment 14005