1. The initial distance between the launching position and the front edge of the bucket will be six feet. This will be increased for each round by a three foot increment to a maximum of the length of the Menstrie Scout Hall, or until no machine successfully lands any balls in the bucket in a particular round.
2. Twenty shots per round per machine are permitted. At the end of each round the score attributed to the machine for that round will be the number of ping pong balls in the bucket multiplied by the distance in feet between the lauching position and the bucket.
3. A machine which scores zero in a particular sound may be entered in the next round.
4. Machine settings, including aim may be adjusted between shots.
5. No part of the machine may extend beyond the line marking the launching position.
6. The power source can be any single Meccano electric (e.g., M0 French, "Cricketball", E15 or other) or clockwork motor. There are no power restrictions for electric motors, Batteries may be changed and clockwork motors may be re-wound as required.
7. Once the machine is set in motion for a shot, no operator intervention is permitted.
8. Any machine judged to have damaged the pong pong ball will be disqualified.
9. There are no size or weight restrictions for the machine's construction.
10. The machine should be assembled from Meccano or Meccano Compatible parts.
11. To assist firing range marshals, fielders, commentators, scorers and reporters writing up the event, the entrant's name must be prominently displayed (e.g. a sticky label).
12. Practice sessions using the firing range will be allowed until the Secretary announces the competition has commenced.
13. Machines which become inoperable during a round will be withdrawn from the remainder of that round, but if successfully returned to working order, may be entered in the next round.
14. The ping pong ball may fly directly to the bucket or may bounce one or more times before reaching the bucket.
15. With the exception of a few nuts, bolts, washers, grub screws and set screws, the machine should finish the round with substantially the same number of parts that it started with.
16. The maximum duration for twenty shots should not exceed three minutes. Any shot fired after the three minute limit will not count towards the score for that round.
17. Entrants may enter more than one machine.
18. Proxy entrants are welcome.
19. In the event of a dispute the Secretary will arbitrate.
20. The winner will be the machine with the highest total score for the competition. In the event of a draw, the winner will be determined by a shoot-off at the greatest bucket range

Although the rules mention only a motorised device they do not specifically exclude a manually operated device. Thus if you want to have a firing mechanism operated by tensioning - e.g. Driving Band(s) or Tension Spring(s) which you have to reset after each "shot", that will be perfectly acceptable.