I bought my first lower back around 2013 (Mag Tactical, looks like they have gone out of business) and it has run fine since. I have started shooting more recently and noticed when the bolt is locked back, the selector was hard to put on safe. Then yesterday, the gun started to fire on trigger release too (free binary trigger?). I thought it was a trigger issue, so I swapped in a Gissele SSA-E. The trigger functions fine, but when I put the selector back in and put it on fire, the hammer does not release (full trigger movement seems blocked). I believe it is being blocked by the selector.

Normally, I'd just throw the upper on another lower, but since I live in a state that has banned all barrels except HBAR barrels, I cannot do that with the currently configured upper. Is there anything I can do, or is this lower just good for the trash?

If your AR diagnostics skills are not measuring up, maybe you might want to start with a fresh mil-spec lower parts kit, and think about installing your spare bolt carrier group  

I might suspect an out of spec selector.    Without any data, it is rash to call the lower scrap.

I did try two other selectors in the lower, which produced the same results. Also, I have read other places that Mag Tac lowers had these problems, that is why I believe it is an out of spec lower.

The two other selectors I tried are in use in other functioning rifles too.

I put in the Gissele in another lower and it functions fine.  I put another milspec trigger into the "problem" lower and it seems to function correctly, it does not hit the selector or drop the hammer on release.  If a lower is out of spec, could there be some excellerated wear that would cause a once before perfectly fine trigger to start dropping the hammer on trigger release over time?  I put the trigger that was having problems into another lower and it did not seem to drop the hammer on release. Ugh, this is a headache

BTW, Fostech bought out Mag Tactical. They still produce that Aluminum/Magnesium lower. If you do get another parts kit to try out, don't discard the original hammer and trigger pins from Mag Tactical. They are longer than standard pins for that lower.