In building my "new" M4gery, I found that the selector detent was way too large to fit the hole in the Century stripped lower.  I also tried it on a Bushy lower that we had and it was likewise way too big for the hole in the Bushmaster.  Accordingly, I used a spare takedown pin detent.  The selector works fine but the question is, is it safe to keep it in there as the detent pin is much smaller than the proper pin or do I need to pickup another selector detent and spring?
Thanks in advance for any help or thoughts.

While the take-down pin detent would probably work for a while, it is way too small to run true inside of the safety detent hole. I would be worried about it flopping around inside the hole and eventualy wallering out or burring the inside of the hole enough that it might lock-up the safety switch in one position or the other.

I'd pick up another detent plunger that fit the hole properly. There's lots of variation in these small parts from one manufacturer to another.

HTH . . . . . Doug

law4fun,

I've run into that problem a few times, myself. I just chuck the pin a cordless drill and file the base until I get a nice fit. You want it to slide easily, without binding.

Thanks for the help guys.  I do appreciate it.  I am relatively new to ARs, having been a die-hard FAL builder for the last 3 years.  A heart problem has caused me to change calibers for the short term.....