Hi Antoni,
The inside of your gun should look clean but not dry, the piston & spring should have a light smear of grease & the piston head a thin smear of silicon oil.
I hold my combro on with elastic bands.
Your velocity will depend on which calibre you're using.
.22 weighing about 14.3 grains will be around 600ft/sec & .177 weighing about 8.5 grains will be around 775ft/sec.
Hope this helps.