Teach me about Automag Pump Kits

[Drone31]

How long does the mainspring need to be? I assume people are trimming them shorter.

[alpha_q_up]

It really depends on a combo of factors, when building/tuning my pump mags I used to start by cutting the spring to be flush with the tip of the bolt, now I start with a heavily used worn gold spring and test it out then cut the spring little and test it the wash rinse repeat until I have it where I like it. Recently I've had luck and most the time them being worn in is enough to make the pump work perfect