Yes the 9mm mags work perfect in the .40. I havent had any problems with either of mine. I continue using the 9mm in the .40 just to make sure no problems arise and if they ever do, i'll know about how many rounds I put through it before hand.

As for the 9mm rounds in the 40 mag. I have tried this also, and yes it does work. However, you will not see me using it like that. I'd much rather use it with the 9mm mag, as those are very easy to obtain. For the moment the barrels are the MAIN concern of anyone who's wanting to convert.

Just so you guys know, I have about 600 rounds through the 9mm barrel while in the .40 slide/frame. There is still no problems that I can see with either portion of the exchange. Regular cleaning and regular lubing, this thing keeps going and going.

I have also never experienced a mag drop in my .40 at all. I have heard many problems with the mag drops, but for me I have never experienced one. And this is using the .40 as a .40. Maybe it likes me or maybe I got lucky and got a descent one.