builder bog piston

[battlemonkey]

I have wanted to make a coaxal gun for a while and have moved away from the idea of a masive gun for something more portable.
I was wondering counld i use this piece of 2in cast builders bog as the piston with equilisation holes drilled through and a ruber disk on the end.
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If not what would be the next easyist design

[f.c]

look at jacks how-to on epoxy casting. i just doubt builders bog would really do the job.