Do you mean DIY MODs or upgrades? There is a difference. (Lighten up guys, he hasn't even responded.)
Work on compression and getting the best seal out of all you parts in line from the piston to the barrel. I use teflon tape on almost all of my guns between the cylinder and cylinder head. A aero cylinder head also work as well and putting a small spacer on your spring guide but I wouldn't recommend it as much for AEGs as I would for a bolt gun. I would also wrap a couple layers of tape around your barre l under your hopup bucking too.
http://www.airsoftretreat.com/forums...?topic=40038.0
(I'm trying this one currently on a M14, but no results yet.)
http://alabamaairsoft.technoprimitiv...opic.php?t=245 (works better with some piston heads than others.)
http://www.airsoftfaqs.com/technical...-nozzle-2.html
(the air seal mod is tricky, but my attempts shown gains just as good as the o-ring mod. I just couldn't get it to cycle more than once.)
http://www.airsoftcanada.com/showthr...ight=ventilate
(BIG DEAL if you don't have one.)
DIY Airsoft is hit or miss and then its mostly temporary, but I think its fun to mess around and see what and were things could be improved upon.
Good luck,
mateba
