Depends what. I run GBBRs so it's a mix of RS, high end airsoft parts and cheap ACM knockoffs.
e.g.: pistol grips need to be RS (and they just feel so much better), stocks I have a RS Magpul CTR (not the PTS one), an ACM UBR (which fits better on WE than the PTS one and costs a fraction of the RS one) and I have a couple of Element LMT Cranes, which are fine for what they are. RIS/RAS handguards, I use the high end (Madbull) versions: they're good value for the money and the rails are the right size.
In some cases its cheaper using an RS part than the airsoft copy. Adding a Badger Tactical Latch, for example, or basic parts like receiver plates, stock tubes, etc.
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