Just built another M4 on a RRA lower and Model1Sales M4 upper.  I've built seven other AR's using RRA receivers and various Model1 kits with no problems.

This one, however, stumps me.  On the very frist outing, BOTH pins would walk out to the right after 15 rounds or so.  I can certainly install some anti-walk pins and fix it..I'm just wondering what the cause is.  Could the hammer and trigger springs be weak?

FCG is M1Sales, as are all my others.

Any ideas?

same thing happened to my DPMS when I changed out the trigger and hammer spring.  At first, I thought I had the pins in backward and the little recessed ring wasn't engaging the leg of the hammer spring...I had just got my trigger pull where I want it, and decided to forget about troubleshooting it any further, so I stuck with the anti-walk pins

If your J spring/pin is present, its REAL hard for the hammer pin to walk.  I have gotten hammers before where they left this out.

well it's there.  I just don't get it.  I think it's possible the pin holes may be a bit out of spec as could be the pins.  I just purchased a set of the KNS anti-walk pins to fix the problem once and for all.