VFC m4 upgrades?

How can I make my vfc my be very consistant, have a REALLY good accuracy and have a almost perfect airseal. Please include all brands and items. also is there anything else I should change out that is "faulty" in the vfc?

You'll want good compression http://www.airsoftcore.com/forum/index.php?showtopic=44944 and make sure that everything in the hop up unit is aligned and literally perfect.

Systema Bucking
Polar Star Nub
Prommy 6.03 TBB
Teflon tape
O-Rings
Shims
Relube
Sorbothane for AoE

As far as thing needing replacing, the Piston, and piston head should be the first things.

As said above, I would change the piston and piston head while you're in the gearbox. I won't recommend specific ones till you tell me what spring you're using and what RoF you're running at.

I suppose we'll start with cylinder compression. Most piston heads aren't at fault, but rather the o-ring is. Stretching the o-ring on the cylinder and briefly applying heat from a lighter can sometimes make the o-ring larger such that it seals better. I have also had great luck with #14 o-rings. Of course, if either the stock o-ring or the o-ring that comes with a piston head seals right, just use that. Cylinder heads rarely leak, but if yours does for some reason, using teflon tape or silicon sealant can seal it up. The stock nozzle has an o-ring and should seal fairly well.

Wrapping some teflon tape or dental floss around the bucking in front of the barrel window and create a better seal with the barrel. The latter option, floss, will probably be better both because it's more effective and because teflon tape will have a tough time fitting in the tight chamber with the bucking.

As for accuracy. Tightbore. I always recommend Prometheus 6.03s if you have the money, but if not, I suggest Madbull as a "budget" option. A hop-up bucking. VFC hop-up chambers are a bit tight, so some like the Prometheus soft I like aren't going to work well. I would suggest a Systema bucking. The above post mentions a PCS or SCS nub. I have found I am not able to really get better results with it or h-nubs provided I tune up my chamber right, but as they are cheap, trying one, as well as an h-nub, wouldn't be a bad idea. Multiple buckings may be in order to test different mound modifications. Unfortunately, a lot of getting a gun to be more accurate/precise comes down to experimenting.

Hopefully that helps.