I don't remember what the ideal barrel length for a VSR10 is, I think it's somewhere in the range timbuk gave, but the reason you don't want a super long barrel is this:
So when the piston is held back by the sear, the volume between the piston head and the cylinder head is how much air your piston's going to move. As the piston goes forwards it compresses the air and accelerates. As it hits the cylinder head the air continues to expand/accelerate the bb forwards. 410-480mm is the point at which the air stops accelerating. It continues to expand, but with negative acceleration (slowing down), so everything past 410-480 is just a waste essentially.
Are you East or West WA?
Real Sword SVD and KWA MP7. Accuracy by precision or volume, the choice is mine.
Own it, paint it, mod it, love it