The first round would not feed when the bolt catch was released.I turned the catch one turn clockwise.This solved the problem for all my mags except one, a ten round Bushmaster.It will strip a round with nine rounds in the mag but comes to a stop with ten.
I'm wondering if I should try turning the catch one more turn.Could it cause problems for the other magazines?
What is happening inside when the catch is loosen or tighten?

As long as the usgi mags function you are OK.  
My 10rd bushmaster only holds 9 rounds. It
didn't feed when I tried it. After I used the
mag some it got broken in and now works fine.

If all of your mags [i]except[/i] the Bushmaster mag, then I would not change a thing.  BM 10 rounders are problematic for some due to the stiff springs.