Just finished reassembling a Gen 9 M4A1, first time working on one. It has a black nylon gearbox, not the earlier clear version.
The gearbox case seems to be a pretty flimsy offering with a dodgy spring retaining setup. I want to experiment with different piston spring upgrades, but I don’t have a lot of confidence in the strength of the gearbox case, even with a moderate upgrade to 1.3mm
Is the box strong enough for heavier springs or is there a way to strengthen the setup that’s there?