AEG's generally don't give a shit about rain. I've played in pouring rain before. Just give it a wipe down after, and if you really want to open it up and check the exterior of the mechbox and interior of the gun body. It's not salt water.
GBBR's would be similar to AEG's, rain doesn't matter at all for them.
I've seen many Systema PTW's go down because of the rain, however.
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