A guy wants me to airbrush on some AR mags. He is going to send them to me and I'm supposed to paint them and send them back to him, in New Jersey. Anyone know the legality of this? New Jersey worries me.

i would not
if you go to cabelas to buy one (lets say you lived in NJ).. and went to order..
link to page to buy 30rd pmag

then click on the (in red) "View All Restrictions That May Apply" NJ is down on there.. All off NJ i would not

Hmm, if they are his and he sends them to you and you do nothing, but airbrush them I don;t see how you are breaking the law. I could see that he might be by owning them if there is a restriction, but you aren't selling them to him, he already owns them.

You're not selling to him. Besides, they may be permanently modified already per magazine capacity limits in New Joisey.

I just moved to VA from NJ... Anything 15 rounds or less, you should be ok. If the magazines are more than 15 rounds, DO NOT ACCEPT!! I know Hexmag makes a 15 round magazine to look like a 30; has a round restrictor inside. If any questions, I'd refer to the following link:

http://www.njsp.org/about/fire_ag2.html

What if he disassembles the mags and only sends you the bodies to be painted 1) it's just a piece of metal at that point. 2) you wouldn't want to paint the internals of the mag anyway. 3) You would have no knowledge of the amount of rounds each mag can hold.

I'm just giving you an idea. I believe that if you're not comfortable with the idea, don't do it.