Don,
Your velocities ARE low. I have a Knight Disc Elite .45 and had an Omega .45 until a short time ago.

Here are some velocity readings using the 200gr SST from both rifles.
Knight Disc Elite .45 200gr SST
100gr 777 ffg 1967fps
100gr 777 fffg 2025fps
110gr 777 fffg 2011fps

T/C Omega .45 200gr SST
2 Pyrodex pellets 2023fps
3 Pyrodex pellets 2362fps
100gr 777 ffg 2051fps
100gr 777 fffg 2064fps

Now both of these guns have longer barrels than your G2 and I wonder if the velocities given by T/C were really from an Omega. Also, 777 is a little hotter than Pyrodex, somewhere around 15% hotter. If I were you, I'd give some 777 fffg a try and see if it still gives you the accuracy you want. I'd expect 100gr fffg 777 to be around 1700fps from your G2 with the Shockwaves. Powerbelts usually ARE about 100fps slower than the sabotet counterpart.