Been playing in my shop (a bit crude since I was looking more at function than cosmetics):

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12:00 made from 1/4" copper tubing with cap and 1/2" pine dowel piston
10:00 and 2:00 made from 1/2" copper stubout w/ 1/2" oak dowel piston
4:00 and 8:00 made from 1" pine dowel with 1/2" oak dowel piston
6:00 made of 1/2" copper tubing with cap and 1/2" oak dowel piston

All are functional, 1/2" copper based units produce superior compression.  Unit at 6:00 is shortest (4" overall); unit at 10:00 is longest (6" overall).  All wood unit at 8:00 is the lightest (1.5 oz.). Each unit also uses a rubber O-ring about 1/4" from the end of the piston.

dd