The rear sight is a dovetail sight I believe, it just needs to be slide out. Though on the plastic it could've been quite tight.
Alternatively you can get Proud's night sight for it. Its 3 dot tritium-style, and can be had in metal.
The G&G barrel do have cycling issue, I can have mine on(when I had the KSC G19) for display but it wouldn't shoot properly with it....The problem with the thread adaptor is that it has a CW thread from the adaptor into the barrel, and a CCW thread(mine anyhow) to the silencer. Therefore you can never tighten it fully....(tighten one loosen the other)
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