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[i]Tophat Adjustments
All Airforce rifles come from the factory with their top hat too far out. Wasting air and causing excessive noise
In an effort to make the Airforce line of airguns consistent the tophat adjustment is one of the most important part in obtaining that consistency.
The tophat is the part that the bolt seats it self against when the bolt is closed. It is threaded onto the valve stem of the tank and can be moved down and up for adjustments in fine tuning the rifle.
When the gun is fired the hammer hits the bolt and the bolt hits the tophat forcing the tophat down which moves the valve stem and opens the valve. This allows compressed air to escape through the valve stem into the bolt pushing the pellet down the barrel. The tophat only needs to move a very small increment maybe 5 to 6 thousandths of an inch to work properly.
The position of the tophat can have profound effect on the amount of air escaping from the valve and the result can be seen in the velocity of the pellet.
You measure the velocity with a chronograph and it is need to correctly adjust the tophat.
What you need to correctly adjust the top hat is:
A caliper or Micrometer
Feeler gauge
Chronograph
I suggest if you need to adjust your top hat start with it .070. This measurement is taken from the bottom of the top hat and the top of the valve. Loosen the screws holding the top hat, and I always give my gun some preload on the mainspring for testing and set it at about 4 on the power wheel. Have a good supply of air and choose the best pellet for your gun that you will use the most. JSB, Crosman Priemeres and Kodiaks are some favorites. Shoot your gun over a chrony and look at the velocity. Now turn the tophat .002