(by jomarx)Take notes the followings:* Metal bushings and reshimming is required for each upgrade.* The Stubby killer is quite hard to increase its FPS because of its short barrel length, unless your going to use an extended barrel (which defeats the purpose of using a 'short' stubby).* High ROF M4's tend to missfeed, its either because of the magazine OR it needs a sector chip (sometimes both).
* SP140/500fps upgrades requires a reinforced gearbox OR just wait for the stock gearbox to break (... Continue reading ...
