Just a heads up I took the trigger apart on my ATR last night and replaced the retun spring. I used a lighter spring from a local hardware store, doubt it matters where you the source the spring from. I did have to drill out the hole that the spring sits in a little but it was very easy. I cut the spring a little long to get rid of some creep but didn't really fine tune it at all.
For a mod that cost basically nothing and took about 15 minute there is a huge improvement in the trigger. It is lighter, with a nice smooth pull and a crisp break. There is still a little creep but not enough that I'm going to bother mesing with it.
Put a spent shell in the chamber and tried dropping, jarring and otherwise bumping the gun to see if it would accidentally fire and had no trouble at all.
Have shot it twice since the mod and everything works great. I highly reccomend this to anyone with an ATR or 4x4.