I'm sure some of the guys can offer a lot more advice than me - I am but a basic tinkerer.
Infact,
@Sitting Duck is a beacon of knowledge when it comes to his spare parts.
Not quite - I have just broke a lot by taking the pi$$ and fitting stuff very badly at first
(I'm the airsoft version of Doug from Scrubs - I have learnt some of the stuff NOT to do)
+1 for AK2M4 - great place, move ya ar$e as some bits sell out quick
Upgrades - a lot of the time badly fitted replacement parts can be downgrades in the end
Prowin, Madbull & others do not come with magic TM dust & over rated imho
I still strongly advise if your barrel/hop is reasonable then build up a new hop/bucking/barrel combo
(if new unit is crap then you still got old one to go back to - strip old unit down, tear bucking, lose circlip = ya screwed)
ZCI barrels are quite good but they are not a prommy
SHS gears are good but not Seigetek
You should see slight improvement IF fitted properly
(plus still believe a sprinkling of luck on bucking/hop/barrel combos)
BUT you might already have a half decent bit of accuracy - sometimes you get lucky & it isn't that bad
So work with what you got, clean, set hop & use very good bb's before you dive into the "must upgrade" route
I'm no expert on accuracy & hop stuff but I know it is too damn easy to make things worse by going nutz
Hence maintain & set your stuff properly first - I have gone back to stock a number of times coz upgrade was $hit
(but I'm still a noob on bucking/hop area)