The Plastic ones actually work...
Plus if you make a plastic receiver out of PLA or ABS... they would last a few hundred, if not a few thousand round... of bursted firing.
But, hey, if you want a printed gun, you ain't getting me to make it for you. Buy your own damned 3D printer and make it yourself... since you never know when a house fire will ruin your day in more than one way.
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greg@gregfolkert.net
"No snowflake in an avalanche ever feels responsible." --Stanislaw Jerzy Lec