Ive gotten RIFs into the US without any issue, including a few TMs, which Customs usually either seize or dremel off the trades. I just pack them in my suitcase, wrap the tip in orange duct tape, put painters tape all over it with "Airsoft Replica" written in Sharpie on the tap. Ive gotten a TM MP7, TM mk23, WA SV 1911, and a few others across no problem (although my bags always get searched on the way through)
I've had a visit after ordering a safariland for a glock 19 "because it's what the police use" I refrained from correcting him and just explained the reasoning then it was released from customs to me, first time it's ever happened even though I had 2 safariland's before and it's never happened since but hey ho it all worked out