Donnie Darko is a cult independent science fiction thriller/drama written and directed by Richard Kelly (Southland Tales) and stars Jake Gyllenhaal as eponymous Donnie, disturbed suburban teenager confronted by Frank, a guy in a rabbit suit who proclaims that the world will end in an exact time of 28 days. The film was a box office disappointment in its original release, but gained a massive cult following upon its video release. The film would later gain a theatrical re-release with a new "Director's Cut" (though Kelly told on the interviews that theatrical version is his preferred and director's cut was just did to explain some uncertain scenes). A sequel, S.Darko (centered on Donnie's sister Samantha), released in 2009 was not as successful and well-received, nor it was considered or supported by Richard Kelly though it has its own minor cult following.
The following weapons were used in the film Donnie Darko:
Custom Colt MK IV Series 80
Donnie Darko (Jake Gyllenhaal) finds a Custom Colt MK IV Series 80 in his parents' bedroom which he later fires once. At least in the close-ups it has a blued finish, M1911-style wood grips, large target sights, a Colt Commander ring hammer, extended thumb-safety, and a extended beaver-tail grip-safety. it's possible that an airsoft (or other non-firing) replica was used for non-firing scenes.
Unknown Pump-Action Shotgun
When Donnie and his friends, Ronald Fisher (Stuart Stone) and Sean Smith (Gary Lundy) are relaxing with alcohol they use shotguns to shoot on bottles and other random targets on the improvised range. Donnie uses unknown pump-action shotgun which may or may not be air gun (or portrayed as such) or even airsoft due to lack of muzzle flash (though the moment of firing is filmed from a far distance), the sounds and the fact that he pumps it a few times before the shot (he may have been charging the shotgun, though).
Sean Smith (Gary Lundy) has an unknown shotgun on an improvised shooting range. He doesn't fire it, though it's implied that he did this on bottles. Due to nature of it's appearance it may be an air-, airsoft gun or any other non-firing replica.