I am satisfied, achieved goal (1377 converted)

[Gibsonvair]

I am calling success. My 1377 converted to steel breech, .22 caliber, 14.6" barrel, folding stock, 9S Gravmag, Buckrail suppressor,2-7x32 AO scope I got the FPE I was looking for with the Magnum Airpower cupped piston and valve plus oversized transfer port. I just had to tighten up the pressure of the piston to the valve and got 13 FPE at 15 pumps, 14 FPE at 17 pumps, 16 FPE at 20 pumps, and 16.5 FPE at 25 pumps. I still need to do some trigger work and accuracy testing, but I have high hopes. On the same chronograph, this beats my springer!

[Gibsonvair]

I also validated the power with my cardboard layer target box. It penetrated 40 layers at 25 pumps I adapted this idea from the Needful Things E-bay guy or Alchemy Airwerks Blog. http://www.alchemyairwerks.com/alchemy-blog

[Gibsonvair]

Well, an easy way to boost your FPE is to just enter a heavier pellet weight into the calculator. Not quite as elated any more. New FPE numbers: 15 pumps=11.74 FPE, 17 pumps=12.61 FPE, 20 pumps equals 13.63 FPE and 25 Pumps equals 14.86 FPE. Still OK.

[triggerfest]

Wow ! Nice job !

How is the pumping effort with so many pumps then ?

[threesuns]

OEM pump cup can make decent power when set up properly. Nice job!

[Gibsonvair]

Wow ! Nice job !

How is the pumping effort with so many pumps then ?

 I suspect the valve volume is larger than stock because I have two pistols side by side to compare. One is the (stock) 10.5" barrel with stock valve, piston, and port. The other is (modified) 14.6" barrel with modified piston, valve, and port.  It is way easier to pump the modified gun than the stock gun.  Conversely, the modified out performs the 10.5" barreled (stock) pistol at 10 pumps and beyond. The only sacrifice is swinging around a longer barrel. I consider the 7 FPE of the pistol at 10 pumps marginal for most of my purposes. Pumping up to 25 is a little painful with the stock gun.