Assuming it wasn't left cocked I doubt it's the spring to blame.
Those pistols have a split ring metal piston seal - I wonder if the problem is just old grease that's hardened and is slowing the piston in its flight, in which case try squiring a SMALL amount of WD40 or other releasing agent at the end of the piston nearest the back of the pistol when it's uncocked.
The barrel popping up thing I have no idea, unless the barrel retaining styrup plunger is similarly sticky?