Well, it's not rocket science, but the same way that the old trigger unit is attached to the gun. It's about 1 year when I fully upgraded a vsr and it was 2 screws and the spring guide stopper what attached the original trigger unit to the gun.
But the stock trigger guard doesn't fit around it and the screw that is furthest back that attaches the trigger to the gun is hidden in the base plate which i can't get to easily because there is lots of stuff near it.
Your going to have to do a self-mod to your stock/trigger guard because of the "quick release" the zero triggers come with.
Depending on what rifle you have your going to need to modify it differently but usually are the same.
Get a file and file down the trigger guard so that your zero trig will drop in. It may take a little time to get the fitting righ but shouldnt be hard. All of us that upgrade our rifles have done it. No biggy and doesnt disrupt the integrity of the rifle.
PM me with a list of what you fitted and how and we can sort it out from there. If it helps you feel better I just did a load of upgrades to my VSR this weekend, and on test firing got 31 fps out of it
the bb litteraly landed 3 feet in front of me
" title="" border="0"/> found I had an air leak in the hop/nozzle joint....all fixed now