I've got a new ASA 9mm upper that the block fits in from the top inside of the receiver..the block I presently have fits so tight that it has to be installed & removed with a rubber mallet..I am being sent another block by the seller....my question is (and I have NOT shot it yet)...those that have used these types, which operates / shoots better a tight block like I have or a loose block that fits in and out with complete ease..and also the block that fits tight also allows the mags to "rock" back and fort a little..does this tend to cause problems? Thanks again for all that reply!!   jackpot

Well, I have an ASA adapter and upper.  But I use it in a Cav-15 (Cavalry Arms).  The adapter fits snug, but not too snug that I can't push/pull it by hand.

Now I did try the adapter in a few standard AL lowers and a few would not even allow it to fit.  I can't recall which it was.  I think my RRA is one and an old pre ban Oly (the old stop sign marked one).  I haven't tried the other AL lower AR's I have though....

The adapter and mag 'rock a litte', but i have no problems with it.  Usually the problems are feed problems related to the mag and not the adapter.

mine is tight in my eagle arms/armalite lower.  can't even get it started in my bushmaster lowers

My fits tight in my Rock River lower, but I can pull out by hand.My gun functions perfect will
the ASA mag block.The only problem is the one
bad follower in a mag.