TPU Piston Pad O-Ring for Finisher 3.X Nerf Blaster

After about a month of using a 3D printed plunger tube for my Finisher, the tube split at the layer line right as the tube begins to narrow because it was colliding with the piston with each fire. The PETG spring didn't help. I designed a replacement piston with slot for a TPU piston pad & integrated o-ring.

The pad cushions impact, dramatically reducing noise & stress on the parts. The integrated o-ring maintains the same seal & power as a normal o-ring.

Print the Piston with slot as the previous piston, 100% infill. Use the same size screw.

2 different TPU pads are provided, one with a skirt for a slightly better seal and one with a slightly wider pad.
I personally use the one with a slightly wider pad since the part of the tube that it impacts most is the lower 20% of the edge, so force is spread through more pad.

TPU Printing Settings:

Filament: Fiberflex 30D
Layer height: 0.2mm
30% gyroid infill
Bottom shell layers: 5
Wall loops 3
Speed: 20 mm/s for everything
Temperature: 200-230C
Fan off first 2 layers

TPU printing tips:
Dry the TPU before each use.
Print very slowly.
Don't require the machine to pull the filament from the spool. 30D is like a springy wet noodle; it stretches until the spool overcomes friction & moves a little, causing a jerky tug on the filament.
Either top feed the filament directly into the extruder
or since this is a small part,
Measure the filament needed and pre-cut filament from the spool and feed it loose into the external port. As long as it doesn't snag on anything, it should print out smooth. My prints were junk until I did this. 
Bonus, you can store the pre-cut filament in an air tight container with silica beads to dry it out if you don't have a filament dryer.