Looking for upgrade advice

[Infidelta]

So I have an Echo1 AK47 BOLT, and I'm looking to beef it up. For being an echo1, it's a pretty solid gun, but I'd like to to shoot a little hard. Have a little more umf, when my bbs hit others(so it doesn't feel like the bb just feel on them). It has a short barrel, so I don't expect it to reach out and touch, just hit harder. I already have a mock surpressor and extended TB inside it. I know the gun also has a stock M100 spring, so I'd like to up that to a M120, if it'll stay at/under 400fps w/.20's.

To just cut to my questions:
To you tech savvy people out there; what internal upgrades should I get? What might you think I'll need to reinforce. I'm just real noob when it comes to taking apart a gearbox and knowing what is real quality parts.
And any suggestions on where I should take my AEG to get worked on?

Thanks.

[Warlord]

for under 400fps with .2g your good with plastic pistons, but it never hurts to put metal teeth piston in. Always correct AOE(angle of engagement from piston to sector gear), sorbo pads on the cylinder help do that and reduce gearbox shell wear. Compression sounds like the next major thing to check on and maybe a new piston head. As far as springs go you can go with m110 to acheive over 400fps with a ball bearing spring guide.

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