I can't speak for the m4 so I don't know exactly what needs to happen on that guy but here is what I can tell you about my scar.
1) shoot it!
The more you shoot it the better it gets. Don't worry about the barrel and changing the hop up just keep shooting it took about 5000 shots before it got really good.
2) tooth floss the bucking
There's a lot of gas power coming out of it. Don't let it escape.
3) glue the nub to the adjustment piece
The nub moves around slightly shot to shot. Gluing it up there with dramatically improve the hop consistency.
3) proper lubeing
Now what I'm going to tell you is not what most people are going to tell you. Most sillicon lube is absolute crap.
http://www.mec.ca/product/5039-747/s...-light-grease/
Go get some of this stuff and use it everywhere in the gun. It's safe. Don't worry about it just use it. This is one of the best paintball lubes. People like it more than dow33 which is one of the only sillicon lubes I recommend. And it will last year's.
Don't use green gas in your mags. Use propain and lube the seals with the slickoleum as mentioned above. The seals probably only need to be lubed once ever few months. However the valve which gets hit by the fireing pin can get lubed once every couple outings. It's the only thing that moves in the mag other than the fill valve. Just worry about that one and that is it!
Here is what I've done with the nosel o-ring. You may not want to do this. I found the seal between the nosel and bolt carrier is extremely bad so I used some dow 55 which slightly swells O-rings for a better seal.
Just having all that done to my scar has made it dramatically better. Unfortunately it's just shy of aeg accuracy and consistency and that is strictly due to the property's of propain. Which draws me to the the last point.
4) Use hpa with a high capacity mag mod. That will get you to the aeg consistency and accuracy. Until this is done I don't think you will find any advantage extending your barrel or changing the bucking.(stock bucking is actually quite good)
Edit: Also do the jb weld hammer mod . The pins like to fall out of the hammer.