until sunday I used a stock m16a2 for like 3 years, 1 of which it was my loaner gun. TM make great guns. My hi capa is stock and it was my primary every sunday for 6 months of the winter (CQB) My Mk23 was stock aswell for about 3 years, performed flawlessly. I started upgrading only because I got a stock AK that was broken, I figured as long as im on there I may as well replace a few things.... then everything

TM M14 SOCOM
semi-auto removed (its used as countersniper) 450 fps
Prometheus spring
Steel bushings
G&P Middle Gear (Super Torque Up)
Systema Steel Gears
G&P Steel Spring Guide
G&G silencer
G&P Tactical Scope Mount Base for M14
G&P M14 Barrel Top Cover (Carbon Black)
Gearbox + motor "foamed" for sound reduction
Heavier battery cables and fuse removed
PDI 6.01
8.4 3300 ma battery's used

But the rest is stock TM for now :)

Back when I had my FAMAS the only upgrades were a spring (330fps) and metal bushings, the rest is stock. My MP5 is stock internally, but has a metal body and some other aftermarket parts (not done by me, aquired in trade).