Damn, that's what I thought. That ruins the entire image I had for building this gun in my head
A guy on Gasguns.info had posted this
"
AGM buffer tube & AGM lower receiver - OK
AGM buffer tube & Prime lower receiver - OK
ACM UBR buffer tube for WA &
AGM lower receiver - OK
ACM UBR buffer tube for WA & Prime lower receiver - OK
"
So I thought there might be a chance this would work with the ACM.