The velocity change is due to, I believe, the physical diameter of the hop system. With the hop turned off, enough air blows past the bb and down the barrel ahead if it to drop the FPS. When you engage the hop, you are decreasing the diameter of the rubber enough to provide a better seal and voila. This would mean that slightly larger diameter bbs than the 5.98mm Airsoft Elite bbs may not suffer from this. But who doesn't engage the hop-up on an airsoft gun anyway?
The body of this gun is super rigid with zero flex at all. And yes you can let the bolt go and it clangs into the front of the body (chamber in the real gun), which is heavily reinforced.
As far as compatability with Marui-spec parts, this has never been a strong point for ICS and I haven't really tried with this gun to see if that is still the case. The only issue I see is possibly with gears and bushings. Everything else looks compatable with other brands. But this has always been the issue with other ICS guns as well.
And finally, thanks alot Kip for hosting my pics. You're a god-send!!
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.