Not sure about weight but always bought just 9mm buffers. This I do know if you use a standard length car 9mm buffer it needs a spacer to keep bolt from over traveling and bending bolt stop. I have three conversion builds with mag block adapters that run flawless. If you have questions feel free to pm me.Not to detract from the good deal OP
Do you guys know if the stern defense beretta 92 adapter would work with this upper?
Also, any specific weight buffers you suggest for the 9mm upper swap?
The 9mm upper game is new to me, but since this is about a 9mm upper I may purchase I just wanted to ask those in the know.