After his Colt Official Police service revolver fails to slay the giant ant, Peterson runs and gets this from his patrol car. Needless to say it packs a bit more of a punch. Agent Graham and several soldiers use them in later scenes as well.
The soldiers at the film's climax use these rifles in addition to the Thompson, several fitted with grenade launchers.
First pic:Thompson SMG on the left, M1 Garand w/grenade launcher on the right.
Colt Official Police
Doomed redshirt Trooper Ed Blackburn (Chris Drake) uses a Colt Official Police revolver. Later, Trooper Sgt. Ben Peterson (James Whitmore) uses a Colt Official Police to shoot at a giant ant.
Colt Detective Special
A Colt Detective Special is found by Sgt. Peterson in the destroyed camper at the beginning of the movie. FBI Agent Robert Graham (James Arness) shoots at an ant with a Colt Detective Special of his own later.
Lever-action rifle
A lever-action rifle, described as a 30-30, is found at Gramps Johnson's store with the barrel bent in half.