Jon Gosselin — Threatens Photog With Gun … Shot Fired Allegedly

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Jon Gosselin pulled a gun on a photog in Pennsylvania yesterday — then allegedly fired off a warning shot before chasing her away in his car … and our sources obtained photos of the scary encounter.

It all went down yesterday in Beckersville, PA when a photog (not ours) followed the reality star home from his new waiter”s gig … trying to snap photos of the cabin where Jon lives.

The photog fessed up … she followed him off the main roads and onto dirt roads … but assumed it was a public road and not private property.

We”re told as soon as she started snapping away … Jon made an aggressive b-line for her … then pulled a gun out of the back of his pants.

The photog says Jon started yelling at her for trespassing … then fired off a warning shot.

The photog says she booked it … but Jon followed her until she got back on the main road.

We”re told the photog plans to hit up local police this afternoon to file a report.

We tried to reach Jon … to no avail.