ICS SG551 SWAT upgrades

[Tstyle]

Hi everyone, firstly sorry if this topic has been mentioned before but i couldnt find anything with the answers i need.
i recently bought an ICS SG551 SWAT as a base model for my first project, i havent worked on an airsoft gun before, always got shops to do it for me, but being pretty handy in alot of trades and being an engineer i feel i should be able to strip down and rebuild a gun with the right pointers...
im interested in doing a few simple mods to start, the barrel being the 1st, i wish to get a tightbore, but does anyone know the size i would need, i believe the original is 370 but guess the longest pre-cut one is 363 which i have seen on a few sites, but how easy is it to change the barrel, i managed to strip the gun down to the point where i was holding the barrel in my hand with the hop-up attached but was unsure how to remove the barrel, i guess the small pin that looked to be holding it in?
if changing the barrel would i be required to change anything else, or is it simply a straight swap??
secondly i was thinking of changing the spring, now i know this is more complicated, but im fairly confident i would be able to do it, so can anyone advice me of the process of removing/changing the spring in the said gun, also does this require any special tools or other parts to be changed??
any other pointers on upgrade ideas would be useful while i have the gun stripped down to complete the barrel etc??
thanks for your advice guys!!
happy hunting..

[Tstyle]

Re: ICS SG551 SWAT upgrades

no body know how to strip a ics sg551 then?
or atleast tell me about the barrel and hop, if i was to replace the barrel and hop unit, how do you know what barrel fits what hop?
or are they a universal fitting? any advice would be very helpful?
thanks