CowCow Technology Upper Lock for AAP-01 Airsoft Gas Blowback Pistol
(Color: Blue)

"Do keep in mind i have a stock upper, however i had to file down some parts of the button that didn't fit. However, after doing so it works perfectly

"This part was difficult to install and did require filing. There were also issues with the latch mechanism properly disengaging (this can be seen in how the stock button has a uniform shelf that slides along the groove of the lower receiver). The fact that filing was needed to even get to spec feels disingenuous to "precision" claim.

With a little more tinkering, I bet I could get it to work fine, but it feels like a let-down when the other products seem live up to their "drop-in" reputation.