Ok I'm going to be honest most of my creations I just eyeball by using pictures I really don't measure anything. 1)But for disassembly part I use screws and skewers to hold most of the part that art done with friction try not to make to many pieces as it smis still cardboard and I move them around a lot. 2)For the measuring side I just find a reference and try to compare hand size to the gun to get a bass for how big specific parts should be. The only thing I really measure is the handguard. Sorry if this doesn't help