my gun was used when I got it - and it had an air leak. It was shooting around 330 with .20s, a new $18 cylinder head solved the problem for me and it was shooting 376 with .30s at last chrono, same internals otherwise...
I would check and replace the o-ring(s) on the cylinder head and possibly piston if you see those being cracked, and possibly use teflon tape around the area that needs to be bored out to put in new internals....
http://airsoftatlanta.com/parts_vsr10.htm - my problem was fixed with part 77733 which apparently went up in price. However, some cheap o-rings would have probably done the job just fine....