Thanks for the tips, guys! I'm a bit of a noob when it comes to AR maintenance, so I'm going to work my way through your posts one by one.
Quoted:
Something is blocking the trigger.
If there were movement of the trigger, but no click, then the hammer did not catch the sear and followed the bolt home.
Since you described that there was no movement of the trigger at all, then there is something blocking it. It may be that the selector switch is loose and moved in the way, or you have some sort of debris in the fire control parts which are preventing the trigger from going forward.
The selector switch seems to "lock in" to both positions pretty well, although it's not as firm as my Bushmaster. The trigger works every time if I pull the charging handle first, but it doesn't work for any followup shots.
Quoted:
My guess is that it is the latter. When you cycle a new
cartridge you do not have pressure on the trigger which allows it to
return to its forward position since vibration helps overcome friction.
When firing, you are pulling the trigger to the rear while all the
vibrations of the cycle and recoil are going on. When you let up on the
trigger the return spring cannot overcome the friction alone and stays
to the rear.
You can test this (if you haven't already taken it
apart and cleaned it) is to make sure the rifle is unloaded and no
loaded magazines are present and you have a safe direction in which to
point the muzzle. With no magazine in place, cycle the action and pull
the trigger. It should drop the hammer normally. Now try holding the
trigger back while you cycle the action. If the trigger does not go
forward on its own with a slight click after the action is cycled, that
will confirm the problem.
Honestly, I didn't try pushing the trigger back forward to see if it
might be an issue with a return spring. I'll have to try that next time
I can get out to shoot, but I don't think that is an issue.
I tried the function test you noted and everything appears to work properly. I racked the charging handle, pulled the trigger, cycled the action again, and let go of the trigger. It moved back to its fully forward position and clicked into place, and worked properly once again when I pulled the trigger.
One way you can tell if the hammer is
not resetting is to pull the bolt back a short distance. The hammer
will provide a bit more resistance than the buffer spring alone. You
should also feel and hear the hammer click into engagement with the
sear. If the hammer follows the bolt back you should notice this too.
Try it both with the trigger pulled and not.
Everything "feels" the same with both firearms when I walk through this process. If I hold down the trigger, I get firm resistance throughout the entire pull of the charging handle. If I don't hold down the trigger, I get a "two stage" effect with a light pull from about 1/3-1/2 the travel distance and a firmer pull for the rest of the distance. Is this because of the buffer tube?