I just bought this hk417. Even out of the box it shoots awesome with .25s ( might goto .28 or 3s) this is exactly what I was looking to do with it. I'm also probably looking a add a miracle barrel but I'm unsure if I'll have to changed the hop up while I'm at it.

The hop up for the 417 is already decent enough, the only thing I would consider is the Madbull 3in1 hop up unit for M4 (just the hop up block, no need for the rest) which I'm 99% sure is what VFC used as a base for making their own.

Doesn't the early 417's have structural problems with the gearbox? Did they fix this yet?

The front of the gearbox was weak - this has been addressed post-2012 based on the last one that passed through my hands.

Anyone (prolly Stealth) know if normal v2 pistons amd gears work in this or is it PSG1 stuff or what?
I know, necro post but i have just a simple question about this gun so necroing this thread seemed easier than starting a new one, plus this is alrdy high on google when i search.

Holy shit. You're back. LOL

Yeah it uses standard V2 parts.
https://www.youtube.com/watch?v=SxoLyjhoRcA

Sweet, that piston looks long to me, maybe the guy in the video has small hands lmfao.
Yup, spring is in the air. Time to get shootin stuff lol.

And last question. Is the motor in this gun going to be able to pull the 420fps+ spring with 13:1 gears and an 11.1 15c lipo?
Im not goin for hig speed just high trigger response, tho i know high speed will be a by product of that.

Barely.