Some pics are a little old so I don't remember everything, but I have parts lists for the Tan M4, OD M16, M14 and SR25.
Tan M4 (G&P based): JG 08 Enhanced gearbox w/ G&G upgraded reinforced piston and a M150 spring, Modify ball bearing spring guide, JG M41 magnum motor, sorbo pad, 6.03 Tight bore barrel (JBU or MadBull), MadBull Shark hopup bucking, re wired w/ deans connectors and 16awg silicone high flow wire. Externally it has mostly G&P externals with a KWA outer barrel (the outer barrel has slits cut in it with cable ties stabilizing the inner barrel), it is wired out the stock. Shooting about 500fps @ 20rps on a 11.1v. Range was decent, surpassed 250feet (could have gotten more range but this was just a backup gun so I didn't pay much attention to the detail in my work)
SR25 (Classic Army based): CA SR25 super torque helical gears, SHS 19 tooth piston for elongated gearbox, M180 spring, Systema magnum, Lonex cylinder head, o-ring air nozzle, Deans connectors, Deans wet noodle wiring, Extrem-Fire SW-PANTHER MOSFET, MadBull v.II black python 6.03 tight bore, MadBull shark bucking.....Haven't chrono'd it yet, I need to do some stuff to the gearbox since it shoots week (air nozzle is messed up).
M14 (G&G Real Wood Veteran based): SHS high torque motor,
SHS high torque gears, King Arms Bearing spring guide, M200 Spring, Prometheus hard POM piston, Modified TM piston head w/ bearings, Solid steel Bushings, New cylinder head, New tappet plate, Systema O-Ring air Nozzle, Systema type-0 cylinder, sorbo Pad, Madbull shark hopup bucking, stock 6.04 tight bore, HS armory extreme power MOSFET w/ poly fuse, Deans. The gun was shooting 650+fps, rof was about the same as a stock gun on a 11.1v. This setup launched BBs easily out to 400feet with the high power level it had.
OD M16 (Mix of JG and G&P for the base): Custom wound motor (re wound the motor's armature and polished the commutator), RiotSC Revolution gear set, Prometheus Hard POM Piston, M150 Spring, Modify bearing spring guide, HS armory extreme power MOSFET w/ poly fuse, 4mm bullet connectors, 14 and 16awg aircraft grade wiring, Systema type-0 cylinder, sorbo pad, MadBull shark hopup bucking. Shot 525fps @ 48rps on a 14.8v. Range was a bit over 300feet.
All guns had the basic stuff like shimming, greasing, improving compression and efficiency, etc. Most guns have g-hop style mods.
edit: The wood stock on the '14 was refinished by myself.
The M16 WAS my favorite, but I don't have it anymore....As of now, I'm digging my SR25. I just got it, so it'll be really great for like a week, then I'll get board and it will become "just another gun" lol.