AURORA | As Bobby Cox strides around the hulking structures, his sense of awe is palpable.

Adorned with a forest green hard hat — across the front of which the words “Pit Boss” are neatly stenciled in crimson cursive — Cox peers upward, marveling at the metal giant above him. He points out minute details with the pride of a parent holding a strong report card.

“He cut those pulleys himself,” Cox says, gesturing at three chrome cylinders in the process of devouring yards of royal blue rope. “Nobody else has pieces like that because he makes them all custom. The whole thing is one of the nicest, most efficient trebuchets anyone has ever seen. It may look simple, but let me tell you, it throws a pumpkin.”

Cox is the project manager for Aurora’s Parks, Recreation and Open Space Department and he knows quite a bit about pumpkins. Specifically, hurling them thousands of feet at velocities topping 400 miles per hour.

Punkin’ Chunkin’ Colorado

10 a.m. to 5 p.m. on Saturday, Oct. 11.

11a.m. to 4 p.m. on Sunday, Oct. 12.

Arapahoe Park Race Track, 26000 E. Quincy Ave.

$3 for entrance one day or $5 for both. Children under 12 are free.

The event will also host pie-eating and costume contests, a pumpkin pie bake-off, and a beer garden.

Visit auroragov.org or call 303-326-8659 for more information.

That’s because on top of his role with the Parks Department, he’s the pit boss and safety supervisor for the city’s annual Punkin’ Chunkin’ Colorado event, where dozens of weekend warriors bring homemade catapults, trebuchets and air cannons out to the plains surrounding the Arapahoe Park racetrack to see who can launch a gourd onto the prairie the farthest. Cox is one of the leading chunkin’ authorities in the country, having been to and helped officiate the world championships held annually in Sussex County, Delaware, where the peculiar practice started in 1986 by a couple of mechanically minded farmers.

Cox knows the ins and outs of how to create a good chunk from the proper angles, materials and counterweight — so it’s notable when a new chunker or machine catches his eye. And John Heffelfinger and his 48-foot-tall Pluto machine have done just that.

“My belief is we will have another world champion right there,” Cox says while ogling at Pluto’s monstrous frame. “Actually, I guarantee it.”

Heffelfinger is the heir apparent of the chunkin’ world. Entering only his third ever chunkin’ event this year, the custom wood and metalworker has already made waves with his specimen of a machine that hurled a pumpkin nearly 2,800 feet  during a practice toss earlier this week; a number right on the brink of breaking the current PC trebuchet world record of 2,835.81 feet, set in Delaware last year by Yankee Siege II. The practice launch may in fact have broken the world record, however the pumpkin was never found due to it being launched into dense prairie grass and waning sunlight, so an approximation was made using GPS coordinates.

The success of Pluto’s inaugural launch is the result of an investment of about 500 hours of labor, and $3,000-$5,000 in parts. Those numbers may seem eye-popping to some, but they’re pedestrian when compared to the nearly $75,000 and some 2,000 hours longtime Colorado chunker Greg Wolfe has put into his championship winning machine, Inertia II. An eight-year chunkin’ veteran, Wolfe is the reigning trebuchet champion of the event at Arapahoe Park, has twice taken top honors at the Delaware world championships and even he is impressed with what Heffelfinger has done in such a short time frame.

“John’s machine is something,” he says. “He’s only been at it a couple years, but he has got the itch bad. He’s going to give me a run for my money this year.”

Heffelfinger will have seven sanctioned attempts to break the world record and dethrone Wolfe as reigning trebuchet champion over the course of the two-day festival this weekend. Each attempt in the adult division — there’s also a robust youth division — must be completed using an 8 to 10 lb. pumpkin, which is weighed on a state certified scale. Historically, chunkers have elected to use fruits of the white lumina variety as opposed to the traditional orange due to the belief that they are sturdier and less susceptible to “pie” or disintegrate into mush before leaving the sling. If a pumpkin “pies” before takeoff the attempt in voided and the contestant is given a score of zero.

In line with his innovative ways, Heffelfinger shirked chunkin’ tradition yet again when he completed his nearly record-setting practice toss with an orange pumpkin he got from a local farm stand.

“I knew if I wanted to be competitive I would have to come up with something different and original and improve on technology a bit,” he says. “And I feel like I’m on track toward doing that.”