Today my 2289 pump grip, Mellon Air power adjuster and 18" Mellon Air barrel arrived!
I pulled the 24" barrel off and installed all the new goodies.
After some initial problems with the power adjuster (basically I put the top screw in too far which impeded the spring) I was able to get it to dump almost
all the air at 15 pumps.
Now with 10 pumps it does 550-562 fps with 14.3 grain pellets. So a high of 10.03 fpe.
With 15 pumps it was 596-613fps. High of 11.93 fpe.
So basically the power adjuster itself gave me a fpe increase even though I decreased the barrel length from 24" to 18".
Note I have a TKO muzzle brake on there as well which people say cuts 10-15 fps (never measured).
My transfer port seal could use some work as I noticed it's a bit bent from all my swapping and manhandling. It's actually a thin bit of (brass? copper?) tubing with some poly tube around it. I believe I got it from a Green forum member sometime ago-- I can't quite remember
I imagine if I replace it I'd gain a few fps.
The extra power is nice, but the biggest thing I noticed is that this thing is DEAD ON now! I always thought that 24" barrel wasn't the most accurate thing out there which was why I didn't keep it on a 2240 a few years back. The Mellon Air barrel shoots GREAT!
Other than maybe
tweaking the transfer port itself and the seal, I think I'm done-- the gun shoots great, is quiet and with the 2289 pump handle is much more comfortable to pump.
Thanks everybody for the advice.