Action film about an assassin. Late 90s early 2000s

This movie is about an assassin that is trying to kill a political candidate, the killer in the movie uses a huge gun from the back of a van i believe, its a gun with advanced sights and machine powered. The scene I remember clearly is when the killer goes and buys the gun from the seller, the setting is a country area possibly a mountain or forest area, when the killer inspects thr gun he tells the seller that the guns accuracy is off, the seller explains that’s impossible and the buyer says to go out by the car on the shooting range and hold this pack of cigarettes, the seller does but looks visibly shaken and when he does the buyer aims perfectly at the cigarette pack and shoots, the bullet goes right through the guys arm, after that he keeps shooting and blows up the car by shooting it and kills the seller.