I am having a problem with my Bushy M4gery.  I was checking function last night, and found that after pulling the charging handle back with no magazine in it and letting it run forward, that pulling the trigger would not make the hammer fall.  The hammer was cocked and everything, but the safety switch would not move to safe.  After playing with it for a while, I was able to make the hammer fall, but in subsequent function checks, its about 50/50 as to whether it will lock up like that.  Anybody have any ideas?

On a new rifle, you need to allow the charging handle to free run forward.  If you ride it down with the carrier, the bolt may not fully lock into the barrel extension, which means that hammer may just be bound up on the bottom of the carrier when you pulled the trigger.

Note: the only time that you can engage the safety is when the hammer is fully cocked back.  Once the hammer start to make it's forward travel towards the firing pin (read bound on the carrier), the bottom of the hammer slightly cams the back of the trigger up, and the selector/safety is blocked from going into the safe position.

Since I'm guessing that you new to the rifle, fully clean the rifle before you shoot it.  There’s a ton of grease/assembly lube that needs to be removed from the rifle before it's first firing.  

Also, only use CLP to clean/lube the rifle.  Bore solvent is good in the bore, but remember to get all of the solvent out of the upper before firing.  Bore solvent and CLP tend to gum up if you let them mix.

I wish it were that simple, but I am letting the charging handle free run forward.  Also, the hammer is fully cocked.  I even opened the rifle and pushed back on the hammer with my thumb to make sure that it was.

Pull the FCG and clean/lube it, and then put it back in.  Chances are that it may have a bur/crap in the group binding up the works, and not letting it reset.

Look at it this way; sooner or later you will need to pull the rifle apart for a good cleaning.  This way, you get your hands dirty a little sooner than the yearly cleaning mark.

Also, when you pull down the FCG, check the hammer and disconnector holes for burs.  Any burs at the pins/channels will cause the problem that you’re having with the hammer not resetting.

If needed, go to first page of AR15.com and look at the left side for the manuals to help you strip the hammer and trigger out of the receiver. If you get lost, just post and we can walk you threw any problems you have getting the parts back in.

[url]http://www.ar15.com/content/docs/assembly/lower/[/url]

Do you observe the same problem if you remove the upper and cock the hammer manually?  In other words, does the lower function check fine?

1) Cock hammer (trigger should engage hammer)
2) engage safety (hammer should not fall when trigger is pulled)
3) disengage safety, pull trigger (hammer should fall)
4) hold trigger back, cock hammer (disconnector should engage hammer)
5) release trigger (disconnector should release hammer, trigger should engage it)
6) pull trigger (hammer should fall)

If any of those steps fails, the problem is the lower.  Otherwise, maybe the hammer is getting bound up on the bolt carrier or firing pin.