Jon Gosselin -- Yeah, I Fired My Gun

Jon Gosselin has no apology for firing a warning shot to scare off a trespassing paparazzo, because he tells TMZ it's within his legal right.

Gosselin says the female photog is the one who broke the law by trespassing and repeatedly refusing to leave his private property ... which he says gave him the right to bust a cap.

"I am licensed to carry a concealed handgun, which I withdrew and used to fire a warning shot AWAY from the paparazza" Jon says, adding, "It is well within my rights under Pennsylvania law when someone is trespassing on private property."

Gosselin is calling the photogs bluff -- she says she's filing police report -- because he's certain cops will tell her a thing or two about trespassing and a person's right to protect their property.

Jon says he's mulling over his own legal right ... because he's really pissed at the pap.

Whether it's legal or not for Jon to fire the shot ... it did the trick.