Still with WE, they really are pumping out new things these few months. They have released an open bolt system that is available in either a complete gun or a replacement kit for the original brass tubed blowback design for the M4 series. The kit comprises of a new bolt, cocking handle, barrel and hop unit as well as the magazine feed lip. The upgrade kit will have a new trigger assembly given for free for the upgrade worth rrp of US$40. pics below show the new system in a WE 4
As you can see, the bolt system looks similar to the G36 series they have made, infact the parts are the same so the availability of spare parts will not be much of an issue.
On the topic of new upgrade parts, WE will also release upgraded magazines for performance as seen on the G36 mags, the design internally will work for previous versions of GBB rifles too but with improved performance. I cannot comment on exactly what type of performance and at what costs but with a little gentle push, I was able to find out the predicted retail price of US$30 or maybe even below! Talk about great value there, some pistol mags cost that much, but time will tell if all this is going to be true when the final product comes out.
Some of you may be already thinking the compatibility of magazines with the new open bolt system for the M4 and SCAR series due to the feeding lips. Fear not, WE has already anticipated the switch of some users with replacement lips. Notice the screw on the top of the magazine? That holds the feed lip down and with a new replacement feed lip, this is going to switch the magazine to be compatible with the new open bolt system with minimal hassle using pre-existing magazines.