Hacksaw is an orthogonal sawtooth with expansion factor equal to 9 that was found by Dean Hickerson on August 7, 1992. The population in generation t = 385(9n) - 189 (n ≥ 1) is t/4 + 1079, but the population in generation 1155(9n - 179) (n ≥ 0) is only 977.
The pattern consists of two parts, a stationary shotgun and a set of puffers moving east. The shotgun produces, and usually destroys, a salvo consisting of a middleweight spaceship and two lightweight spaceships. The moving part consists of a blinker puffer 1 and two period 24 glider puffers whose output gliders destroy each other (with help from an accompanying middleweight spaceship). In generation 385(9n - 189) (n ≥ 1) (and 228 for n = 0), a salvo hits the back end of the row of blinkers, causing it to form a blinker fuse that decays at 2c/3. When the row is completely gone, a new row starts to form and a spark is produced. The spark is turned into a glider by an accompanying heavyweight spaceship; the glider is turned into a westward lightweight spaceship in generation 1155(9n - 127) (n ≥ 0) by interacting with the glider puffers. The 3-glider synthesis of the lightweight spaceship is due to David Buckingham. When the lightweight spaceship hits the shotgun in generation 2310(9n - 184) (n ≥ 0), another salvo is released, starting the cycle again.
The idea for this sawtooth pattern was suggested by Bill Gosper.
