How To Replace Your "Firing Pin Stop" In Your WE SCAR-L:
If you're running CO2, get the new "firing pin stop". It looks like
this. I am in no way endorsing Evike. I am simply providing an example of the part in question. My understanding is that this stock part has a high failure rate. If you don't feel it's important, then don't get it. It's 10 bucks (US), and if you don't mind a small amount of technical work it's easy to replace.
For WE M4 users, it is listed as "Part #066" in your manual. For WE SCAR-L users, it isn't even listed in your manual. I can't speak for the WE M4 users, as I only have a WE SCAR-L, but I can give a rundown of what you will need to do in order to install this part. It is not as daunting as some people might think.
1. Remove your Lower Receiver - pop the pin out, slide the lower receiver forward, then remove it.
2. Locate your Fire Selector switches, and remove them - turn it to 'A', and continue turning it until it is pointing at the 7 o-clock position; locate the small hex screws on both levers; PAY ATTENTION - there is a small steel bearing, sandwiched between the lever and the receiver, held in place by a spring.
3. Remove the steel part of the Fire Selector that the levers were attached to - I find it helps to rotate it while pushing it towards the right side of the receiver. PAY ATTENTION - to its orientation before you remove it. Note the positions of the 'grooves' that let the Fire Selector do its job.
4. Locate the small flat-head screw, found above the Magazine Release button on the right side of the receiver. Unscrew it.
5. Locate the small star-head screw, found inside the receiver, directly above where the grip would be - Unscrew it; you should see (looking down from above, towards the bottom) a second star-head screw near the front of the receiver - you do not need to remove it.
6. Lift the Trigger Assembly out of the Lower Receiver - it helps to push from the trigger on one side, and left from the top. PAY ATTENTION - there is a small, rectangular piece of steel that has a very small 90-degree bend to it (it would look like a capital 'L' from the side); this is on the right side of the Trigger Assembly, but if you rotate the entire object, it may fall out of its position.
7. Locate the part to be replaced. PAY ATTENTION - there is a small spring pushing down on it.
So there you go. You can replace a very important part of your GBB, and you didn't even need to get into the really fun stuff inside the Trigger Assembly.