Breaking down a VM-68 into parts and narrating each step along the way.
Find VM-68 parts forsale online at: http://www.baccipaintball.com/parts/semi/vm-68.html
The thread for the screw to connect the m-16 lone star grip is 28 tpi.
The length of the cup seal in this VM-68 is 1.35 inches but you can typically use standard non piercing cup seals that are 1.285 inches.
I recommend drilling the port on the valve out when using the shorter length standard cup seal.
Find Dan on google Plus at here
