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After a bit of searching, I found another puffer in the 8-wide tube:

x = 8, y = 28, rule = B3/S23:T8,0
3bo$5b3o$2o3bo2$4bo$2bobob2o$bob5o$ob3o$ob4obo$2o2bo2bo$2obobobo$4b2o$
2ob2o2bo$4bo$3bobo$obo4bo$o4bobo$4b2o$bo3b3o$bo4bo$3o$2b5o$4b3o$4b3o2$
8o$8o$8o!


Is 5-wide the lower limit or could one ...

Thank you!

I haven't found any puffers in the 8-tube but they exist for sure in any tube with a width 9 or greater. I'm just using normal terminology for the things because I have no better way to refer to them.

x = 9, y = 19, rule = B3/S23:T9,0
2bo3bo$bobobobo$bobobobo$2bo3bo$3b3o2$3bobo$3b3o2 ...

A period 8 lightspeed spaceship that only works in a tube that's 8 blocks wide:

x = 8, y = 32, rule = B3/S23:T8,0
4bo$3b3o3$3b3o$4bo4$4bo$4bo$2bo3bo$b3ob3o$b3ob3o$bobobobo$2b2ob2o$2b2o
b2o4$3b3o2$3bobo$4bo2$2o5bo2$2b5o4$8o!


A 9-cell ancestor of the spaceship:

x = 8, y = 2, rule = B3/S23:T8,0 ...