I am using ISMI springs for a 1911, which are the same as the springs for the XD Tacticals, as far as I know.
With a empty gun with the striker down, I can, while holding the trigger back, I slam a mag in like I'm doing a reload, and have the striker reset when I have anything less then a 20# spring in it. If I have a snap cap in the chamber, and one in the mag, and do the same thing, the slide will slip out of battery about a 1/6th"- 1/8th".
I know a lot of people shooting XDs without this problem, but they don't shoot as fast as I do (3-5 second reloads compared to my 1.4-1.8 second reloads)
I like shooting my XD, because it's about the same as the gun I carry every day, but if I can't get it to work soon, I'm trading in in for a CZ 75 SP01.