The setup on phantom feeds are like that for a few reasons. Biggest one is delrin is forgiving. Being the threads are so fine they will cut there own threads in the delrin. Creating a tight friction lock.
Also makes timing the threads not need so there no problems with ball sights lining up in the right spot. So matching a feed set would not be needed. ( think how a barrel threads on one marker alingins nice and then throw it on another marker and its off)
The same idea can be used with aluim. Only problem comes when you decided to take it a part. Once they go together they tend not to want to come apart.