Unlike everyone seem to suggest I start out with GBBR. Also handle& own PTW, and AEG before
In General,
Magna System (WA):
If you're coming from a real steel AR-15 gunsmith or know it all, this is the best. The only thing new is the hop-up and nozzle. Both are easy to learn. The main draw back of this system is parts breakage. I suggest you use the lightest possible bolt carrier and run CQBR length Inner barrel to keep fps down. DO NOT use NPAS for Magna. It's a bad design, and a main source of headache.
- Most realistic (operationally) GBBR
- Lots and lots of parts available, avoid anything but steel (or AR-15) on moving part
WE AWSS (brass tube): Is consider the most reliable GBBR if you upgrade the internal firing to steel. Even tightening all the screws, the gun is made of pot metal and will eventually wear out. The biggest down side of this system is that it's not suitable for Full auto (ROF is relative low and you can cause the nozzle to freeze reducing efficiency)
WE Open Chamber (Open-Bolt): is the new WE system found in PDW, M14,G36, SCAR, L85, and now AR-15. It has significantly higher kick than AWSS system as well as higher ROF. All in all it is considered equal or superior to the AWSS in everything except nozzle reliabilty. The Nozzle is made of plastic instead of stainless steel. As such when a gun double feed it is a likely scenario the front nozzle will break, and replacement will be needed.
KJW (Tanio-Koba): is considered as out of box game ready GBBR. It uses thermold magazine (slightly larger than GI mags, some double mag pouch will not fit two, namely SDS (specialty defense system...US Army Contractor for gear) The gun is the most AEG compatible GBBR currently available. The biggest issue for the system is the rubber band breaking and lack of aftermarket support (compared to the rest)
KSC's System 7-Two is a similiar system to Magna only it's more reliable and more efficient in gas. However the biggest down side is the poor KSC hop up design (ball bearing as hop up nub)
What would I recommend?
WE Open bolt, mainly I suspect WE will become the Marui of GBBR. The biggest issue with GBBR like real steel pistols are that the magazines are not interchangeable. So far WE STANAG has the most platform compatible (AR-15, SCAR, PDW, L85, and Custom-shop M249) Although the parts are not prefectly durable, alot of parts needed to be upgrade are interchangable with other platofrm (ie trigger set of WE AR-15, PDW, SCAR, G36 are interchangeable)