I know there are some WE rifle GBB users here, and so I am posting this to share my own WE rifle project. I've owned the Gen III WE MK16 for a little over a month now, skirmished with it, changed parts in it, field stripped it dozens of times, and fired over 500 rounds in it. I am looking to make some more modifications to it, and therefore looking for opinions/further suggestions.
First off here is a picture of my MK16:

I painted the stock, pistol grip, the middle and lower rails, the foregrip, flashlight, and flash hider, all with Krylon OD Green Camouflage paint. I used a can of Krylon flat matte finish over it. It's a nice and dull OD color. My exterior furniture is an Action/Guarder Reflect scope, G&P tac light and G&P foregrip. The replica is robust and very sturdy, however after about 4-5 magazines expended you will need to tighten a few screws. Overall the exterior has performed outstanding; my only complaint is the stock is slightly wobbly and the pistol grip gets loose easily(fixed with a couple of twists from a phillips head).
As far as the internals, I have installed the RA-Tech stainless steel NPAS system, which was an absolute pain to install manually, but it is performing fantastic. The pro to the stainless steel system is that it comes with a nifty tool that will allow you to adjust the valve(and FPS) without removing the gas block (I think I am saying that part correctly). Here is a pic of the stainless steel NPAS:

Now, the only problem I have had with this replica, is located in the trigger assembly, which I had issues with out of the box. I will include a picture, as I cannot find the part number on the manual. This little piece started to bend, and eventually fell off within a week of owning it, and I have since had to super glue it together. It has something to do with the charging handle pulling it apart, and I speculate the same damage is occurring when the replica recoils. If anyone has had similar problems and knows a solution on fixing it, please let me know. Here is a picture of the part in question:

Okay, now what I would like to do to finish this project is fairly simple, and this is where I need your help. I cannot for the life of me find an inner barrel besides the RA_Tech. The reason being is this GBB inner barrel differs from AEG due to the hop-up system. On their website it simply states 'tight-bore' but does not give any specs. I am looking to extend the inner barrel to 363 MM, or M4 length. To hide the longer inner barrel I am planning on slapping this Madbull barrel extension:
http://www.airsoftgi.com/product_inf...oducts_id=3477
The last thing I was considering was replacing the finicky stock WE hop-up with the 'Stinger' hop-up. However, I have no idea if the upgrade is worth the money.
I apologize about the novel, but to recap here is what I am looking for as far as suggestions/opinions:
1. Any solutions to my trigger assembly issues?
2. RA-Tech inner barrels, are they good and at least 6.03 in diameter?
3. Stinger hop-up, worth the hassle of buying/installing?
My closing thoughts are this: This GBB rifle replica is my first, and after 500 rounds, I love it. It hits hard, too hard for TASO (chronoed at 423 at TACPB with green gas). The field stripping is a blast, and I love cleaning it. I highly, highly recommend the Bioval .27 BB to use with it (yes they are expensive, but worth it). And after owning 7 AEG's (from bottom of the barrel to high end) I can say that I will never go back.