[Reckless]

+1 prommy barrel

for hop up .. I perfer modify 'accuracy' hop unit, ARS rubber with bump shaved, and SCS

.. as for length .. I beleive general consensus is a bore up kit is 'needed' for barrels over 509mm

if your target max is 400fps .. and you've got full kick ass seal with a M120 spring.. your gonna possibly already break that limit with a 509 6.03 prommy ... it's also strongly recommended that a full cylinder be used for anything over a 363mm

for me personally gearbox-barrel wise... full cylinder, ARS piston/cyl head, prom nozzle, M110 spring, at the moment I'm liking the Madbull half steel rack pistons, modify hop unit, ars rubber, scs , 509 6.03 prom barrel (end the barrel just inside the silencer, basically just clear the outter barrel) .. TM EG1000 motor, basic set of torque up gears (I personally haven't had much luck with helical and half tooth requiring Gear sets.. but many have.. nor have I really needed them) .. a raptor drop in trigger mosfet thing. and run a G&P PEQ with a 10.8v battery .. shim the hop and the inner barrel for as little to none movement as possible.. etc ..

mind you .. not much of the above is drop in, or plug and play ... infact it kinda rides the blurred line between DMR and AEG sniper rifle

if you take what you have, put the money/time into the barrel and the Hop rubber, make sure your FPS is consistant , run good bb's (aka BBbastard .3's or atleast .28's) ... run your inner barrel length to clear your outter barrel ... barrel quality means way more then barrel length.