I am building a totally mini combustion and I want it to not only look good but to work good as well.
I am using a toy guy as the housing and everthing is going to ge inside of it excaet for the cap of the bottly, which will mount just outside the back of the gun.
I am planning to use either a 100mL or a 200mL cough syrup bottle (as both will fit inside) but I don't know how long I should make the barrel....

Also, Is something like a 1/4 inch or 3/8 inch copper line any better than a pen tube?