The triangular barrel has been hit/miss for most. Some can get better groups with a full choked 12 ga and others claim it's a tack driver. Regardless the barrel is considered a "Sporter weight" and needs plenty of cool down time between shot strings. I'd go buy a sand filled "Egg Timer". Shoot a round then turn the timer over. Don't fire another round until the sand runs out. Repeat for a max of 5 shots then take a coffee break. Most any sporter weight barrel will heat up pretty quickly and isn't really the best option for target or varmint shooting. The stock may improve it somewhat but the stock won't make the barrel heavier or make it run cooler
It has a nice action but the only real cure may be something like Benchmark, Bartlein, Krieger, barrel in a much heavier profile. Sendero, Heavy Varmint, Heavy Palma, or my favorite, an MTU profile.