Can a convicted felon buy nail gun?

A nail gun is useless as a weapon, and if you pull that out then someone else might pull a real gun out and then you'll really be in trouble. It sounds like you probably deserve the hassle you're getting anyway.

other than being an incredibly lame way to enter a gunfight (only Mel Gibson can kill with a nail gun)

I just want you to think about what you will tell the judge. Something like:

"it seemed like a good idea at the time, in retrospect it wasn't too good..."

Am I going to give a convicted sex offender self defense advice hmm no you deserve whatever you get or worse.

Baseball bat by the door might be better. Or call the police, if you can prove the harassment they might help you out. What state do you live in, I can research some laws in your area and get back to you?

Nail gun is probable okay, it is the ammunition you can not possess or buy.

you watch too many movies nail guns don't work like that

yes, maybe with a signature.

LOL, ok sure. But, you deserve what your getting.