[JustASimpleSniper]

While it was not a VSR-10, one of my rifles has a screw-in air nozzle. From repeated firing, it would sometimes come loose and give me an awful air leak. Some teflon tape fixed all that. As earlier stated, in majority of cases, there is no leak, but if you do have a leak, it sure can make a difference.

 

[JustASimpleSniper]

Piston weight may or may not increase fps. It may induce joule creep increasing FPS, but at the same time may slow it enough to reduce FPS. Besides that, maybe a thick foam dampener on your cylinder head, the little bit of lost volume may drop it.