I'm still trying to figure out WHY he needs to upgrade his ICS M4, in another thread he was told to leave it as it is and just get a better hop up rubber and a tightbore, yet highny is feeling likehe'll be outgunned on the field unless he goes for fullbore top notch upgrades that really won't improve his playing ability. Old saying around here, Poncho I think, "Upgrade the player, not the gun" still stands out immensely. First I'd do if I got a new gun, whatever type, is use heavier ammo which is a proven way to increase range and accuracy. Second, metal bushings, a decent spring (such as a Modify t90 or 100),a better hop up rubber, maybe a tightbore and bearing spring guide................... massive improvements there, I wouldn't go much past that because it's largely more of headache to deal with. Over all my years of fixing, troubleshooting and pgrading guns, the most reliable and accurate have been those with very minor upgrades. The largest pain in the ass guns and most unreliable have been with huge upgrades, such as full tune up kits by the top manufacturers, and tose clients that decided to buy a bunch of parts from different brandnames because it looked cool, only to give a gun tech 3 to 20 hours worth of work to get shooting right. KISS VERY much applies to airsoft upgrades, upgrade what is needed and replace the parts that are known to be faulty stock (such as the G&P tappet plate, usually goes within the first 1000rds).
Keep this in mind, it's the BBs that hit the players that makes them call hit. Start with quality ammo that will be stable in flight for longer ranges, and penetrate brush easily. Minimum is 0.25g BBs. You will get the best performance out of 0.28g BBs (recommend Bastards) Unless ICS has changed their stock fps, used to be 330fps with 0.20g BBs........... there really isn't a lot you need to do to upgrade the performance. Remember the guy that replied to your hread that said the more you try to upgrade your ICS M4, the more problems you'll have with it. You ask, we reply, up to you to sort out the best course of action from the responses. There are a lot of people on here with little experience that will tell you one thing, there are a lot of others with a lot of experience that will tell you the truth. Up to you to decide what you want to buy.