I too use an ASA upper and have found some interesting things about my mags!
First the upper does not have anything to do with the mags dropping or not, they don’t interact very much! The only thing that touches the mag might be the carrier and differently the bolt to strip rounds off, but no other interaction is going on with the mags and upper.
I have been using a top loaded ASA mag block with my Bushy and now with a dedicated RRA lower.
Both had some issues with mags, first issue, always buy good mags! All of my real Uzi mags work very well; some of the semi generic mags double feed and might fall out now and then. But the no name shit cheap steel mags are the worst! They don’t lock in, cant keep rounds in the pipe, and let more that two or three rounds feed correctly I should go and play the lotto that day!
Now one of the problems has been fixed by giving the Mag Catch one more turn to lock the mags in with, but the damn feeding problem is killing me.
I bought the gun for fun, I never envision myself defending my home with this, and it is for range and plinking duty only! With that said I still want a reliable weapon to use and to bump fire at will!
I can’t tell you how much fun it is to bump fire a 9MM AR at the range!
I believe I will try a different mag adapter soon, I will keep you all posted!
Here is a pic or two for refremce: