The Smith & Wesson model 29 is a revolver produced by Smith & Wesson on its N frame line, champered in .44 magnum and can fire up to six rounds. It was seen in Lethal Weapon 3 as Jack Travis' sidearm of choice for the climax of the movie, replacing the Walther PPK.
Travis is seen pulling his revolver on Captain Murphy and holds him at gun point to take him to the LAPD impound to recover all his stolen weapons and ammo. He is then seen loading his Model 29 with armor piercing bullets while he and his men load up on weapons to take back their hideout. Travis then uses it in a brief shoot out in the subway while Riggs is chasing him through the tunnel.
He then uses it to fire his armor piecing rounds at Sgt. Cole, until Riggs comes to her rescue and disarms Travis.