Answer:
The choke in the end of the barrel
Explanation:
The choke in the end of the barrel is what tightens the shotgun's shot pattern. The choke basically prevents the pellets from spreading by reducing the width of the barrel of the shotgun. The pellets are fired and travel down the barrel/choke of the shotgun, once the pellets leave the end of the gun is when they can finally begin to spread. Without the choke the pellets leave the barrel of the gun and are allowed to spread wider, but with the choke they have a very limited spread.
