It's under Main Shoot Rules, Rule 3
3. EQUIPMENT TESTING
The Organisers must reserve the right to Chronograph any Rifle or Pistol used at any shoot that is subject to the BFTA rules, to ensure compliance with legal requirements. This can be done before, during, or after the shoot at the Chief Marshals discretion
a. The BFTA has declared a maximum pellet speed for rifles of 5 fps below the 12 ft/lbs limit; this is for the actual pellet being used by the shooter on the day.
5fps below 6 ft/lbs will apply for pistols.
b. (Non Grand Prix Series Competitions) A minimum of one registering shot and a max of 3 registering shots will be allowed over the chronograph, no power adjustments are permitted once the competitor has started the competition. Failure of the gun to comply with 3a. above will disqualify that gun for the whole event. Any competitor whose gun fails the chronograph test will have their card marked as void but they may complete the course if they wish with another gun (See Rule 17 - FIRING LINE CONDUCT) to help maintain the group they are shooting in.
(Grand Prix Series Competitions) A minimum of one registering shot and a maximum of 3 registering shots will be allowed over the chronograph, if the gun registers over the Current Legal Limit the shooter will be asked to remove the gun from the course. If the gun registers over the BFTA Limit but under the Current Legal Limit the shooter will receive a YELLOW CARD. On the issue of the first YELLOW CARD the shooter will receive a warning, will be allowed to carry on with the Competition and his/her score will count. On the issue of a second or subsequent YELLOW CARD during the season the score will be void.
c. Deformed pellets may not be used for the testing process (see Penalties, Rule 14) and to this end the Chronograph Marshal may request visual examination of pellets before loading and/or after insertion into the Competitors Gun but before the breech is closed.