Just finished my 2nd lower build (first was about 8 years ago so I could consider this as a first), DPMS lower with Model 1 Sales internals.

THe problem is that with the bolt locked back (eather by inserting an empty mag and pulling back on the charging handle or by pulling back and manually pushing the bolt release) the safety won't move from "Fire" to "Safe".  It will move about 20-30 degrees toward safe but then it stops.  I can move it normally from "Fire" to "Safe" while the bolt is closed and then pull back the bolt and lock it in place, but I have noticed that when the bolt is about half way back, that it meets some resistance.

I have set the hammer with the upper removed with by hand and with no added pressure on the hammer (like when the bolt is closed) there is a clearance between the back part of the trigger and the safety.  When I apply a little force on the hammer (Down toward the trigger as if the bolt was back) that clearance is gone.

When I was installing the safety, I did have a problem getting it to go into the seat on the right side of the lower.  It appeared to be hitting on the back part of the trigger causing the safety to be forced up.  By some blind luck (?) and some wiggeling and a few choice words, it finally went in.  

As I said, this is basicly my first build as I can't remember alot about the one I did in '96, but something just doesn't seem right.

Thanks for any help.

Fully guesing that you have all the parts in correctly,  Model 1 set out more than a few triggers that were out of spec.  The rear portions of the trigger were the selector rides over were not milled down low enough from the start.

Your choices would be to either send the trigger back and get a replacement, or do as others have, which is to straight file the back of the trigger upper flats down to spec (enough to allow the selector to slip into safe mode when the hammer is cocked back).  

Note: When the hammer is not cocked, the bottom of the hammer cams the back of the trigger up, and will not allow the selector to lock into the safe position.

Thanks Dano523.  Now that you mentioned it, I do remember something about some M1S triggers not being in spec.  Forgot all about it until you said something.

Looks like I get to take it back apart and get the trigger right.

Thanks again.