Is machine gun lulu still viable??

I'd say it's viable. What I usually build is:

[ or]

It works fairly well, especially against bruisers, since you can kite them really easily. Only consistent problem is that the items are expensive, so it's hard to reach full build if you don't get fed.

Does magic damage on hit even crit? o.o

If it doesn't I don't see why PD would be in there. If it does, ignore this.

It's not very good.

Lulu is a utility mage, not building AP or CDR turns you into a mediocre short range auto-attacker.

I honestly didnt know that this was a thing really cool though ( don't reccomend for ranked though)

depends on your definition of viable.

you can make it work but it's not going to get you into the LCS

lots of stuff can work on Lulu. I built gunblade + trinity + IE on her in a game not long ago and won the game pretty handily. it certainly wasn't better than a normal build, but it was fun.