What holds a RRA 9mm mag will in the receiver?

[Hang-Fire]

The title says it all. I just ordered a Rock River 9mm mag well adapter. I was wondering exactly what holds the mag block in the host receiver.

HF

[Snake RAH]

A setscrew in the front bottom of the mag block.

[Hang-Fire]

A setscrew in the front bottom of the mag block.

I was wondering how secure the mag block is. Will I have to worry about ejecting it out of the mag well, or have you guys found it to be pretty solid? Sorry, I'm building my first 9mm AR.

[Snake RAH]

If you tighten it to hand tight (and NOT He-Man hand tight), it will be secure enough to stay in your gun.

The magazine release on your lower works with the magazine (either Colt or modified Uzi mag), and doesn't put any downward pressure on the magwell block, so once tightened, it doesn't move.