Last Sept. I bought a .177 Walmart Shadow, and installed a .22 Gamo barrel into it about a month later. I had bought the barrel from Rich, I'm guessing it was a take-off from a .20 conversion he did.
I enlarged the port to 5/32 (.153), because I found that this seems to benefit the .22 guns. The spring in it is an unknown Crosman spring (not a Quest spring), that happens to work fairly well. It's a tighter fit on the Gamo guide (this one has the "skinny" factory guide) and is less twangy than the stock spring, although the power is about the same. I also have the stock spring and tophat spacer to go with it.
It shoots CPHP's at a little over 700fps.
It also comes with a "Shadow Supreme" muzzlebrake, uninstalled.
In all honesty, I'm not desperate to sell it... but I wouldn't mind trying out an MP513 or an RWS34 if I could get enough for this rifle.
If interested, let me know...