I have a Bushmaster lower that was built (by a class II FFL) from a kit. it is apparent that he at least used an M16 hammer (ground off to AR15 spec.). He may have used more M16 parts in the trigger group, I can't tell. Regardless, the selector is an AR15 selector. It doesn't lock securly (tightly) into the safe or semi position. It clicks as if the retaining pin seats into the detent but there is some play. I have checked the retaining pin and spring and they are fine. I want to check the detents in the switch but I can't seem to get it out. I haven't tried to forced it out, only pull it out.
What am I doing wrong?

Did you remove the pistol grip yet?

If you've got it between safe and fire and whack it with a punch it ought to come out regardless of whether the grip is on or not. Sometimes I have to remove the trigger first.

for the love of God don't whack it! just remove the grip

Perhaps I wasn't perfectly clear when I stated that I checked the spring and retaining pin. To do that, I removed the pistol grip. Once the pistol grip was removed and the spring and retaining pin set aside, I tried to take out the switch by hand using no tools. It would not come out. Should I use a punch and push it out? Does it have to be in a certain position to come out?

Mine have always come out freely after removing the grip.  Make sure it isn't binding on the trigger group in any way and then tap it lightly with a wooden dowel.

You don't need to check the detents in the selector to see if it's an auto selector. The auto selector has LOTS of clearance cuts in it, the semi selector just has one large clearance cut for the rear of trigger. Cock the hammer, remove the pistol grip, spring and detent, and the selector should come out.

If the upper hammer hook is ground off of an auto hammer then the hammer is no longer auto.

[b]Full auto[/b]
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19406[/img]
[b]Semi auto[/b]
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19427[/img]

Cock the hammer.