My hammer is following the bolt forward as it is closing after firing.  The milled notches in the hammer are fowling on the back of the firing when they meet.  Sometimes I am getting a "double" when it fires (not good).  What do I need here?  New hammer, trigger, bolt carrier?

When executing a function check, everything is normal.  This only occurs when firing.

Any help is appreciated.

With the upper open, pull the trigger and hold it back. Now push down and back on the hammer until it stops. It should click in place. Now release the trigger and the hammer should catch on the hook of the disconnector. Does it?

See the post above.

Also - this test might pass - but may fail when firing.  The disconnector is either not holding the hammer back, or, the hammer is slipping off the trigger when the bolt carrier slams home.  If you are getting doubles - the latter is more likely.

First - make sure it is assembled correctly - and that the disconnector spring is installed into the trigger.  You should be able to push on the disconnector and it should bounce right back into place.

chrysler.websitewelcome.com/~user1010/byor/lower/partsbig.jpg

The function check works as it should.  All springs are installed properly.  Do you think I have an out of spec part?  Hammer or trigger?

Tweak,

Not sure what you mean by "horizontally", but the hook engages the disconnector securely.  I am thinking the problem resides in the catch on the pivot end of the hammer or the front face of the trigger.  The receiver and parts are all brand new.  The problem started to show up after the first 100 rounds.  The lower is an Olympic and the internal parts are Bushmaster.

I'm going to replace the hammer with an M-16 hammer and see if that cures it.  If so, I will order another AR-15 hammer or take the M-16 hammer to the machine shop for modification.

Yes, middle hammer hook engages the disconnector as it should.  Disconnector spring is good and everything moves the way it is supposed to when a function check is conducted.  SOMETHING is going wrong when the weapon is fired.  Not every time, but 3-5 times in a 30 round magazine.  I'm thinking hammer or trigger out of spec.

Yes I do.  What do you have in mind?

When a rifle starts acting goofy, if the hammer, trigger and disco surfaces don't look excessively worn, the first thing I do--and the cheapest thing, BTW--is to thoroughly clean the gun and replace all the springs that may be in any way connected. Only then do I start on the expensive parts.

You haven't replaced any parts lately, or had the gun apart, I don't suppose?

No it's a new gun, with all new parts.  I will try the mallet test today and see what that does.

Here is the subject weapon throwing a fit...

With the trigger at rest, pull the hammer back until the hammer's disco sear and the disco sear are as close as they can get, then take a photo.  The distance between the two should be around .003, and if the gap is larger than this, the disco will need to be retimed to close the gap (material removed from the bottom/front of the disco where it rides on the top of the hammer which cams the disco father forward to retard the reset release).

Simple put, it could be a combo of the gap being too large (advanced hammer release on reset), and you just dancing the trigger a short distance with it doubling the rifle/releasing the hammer off the disco and it riding it down with the carrier (released before the bolt had fully locked and the unlocked bolt preventing primer ignition).

Myself, I like the set the disco release just before the trigger comes back to rest (read .001 gap).  This prevents the operator from accidentally bumping the rifle since the trigger must be fully released before the hammer can reset back to the primary sear. And, since I do stone the hammer sears to take out the unneeded creep, it insures that the trigger sear is in the correct position to retain the hammer on release, and not allow it to bounce past to fire the rifle (fire on trigger release).

Quick question here as I just noticed a problem with a new build that is very similiar.

I've had a couple times after firing a round, when I went to fire off another, the bolt was closed on a live chamber, but the hammer was not cocked.  

The ONLY times I had this happen is when I was trying to bumpfire from the hip (read, holding the forearm in one hand and feathering the pistol grip and trigger with the other).

I've done the function checks and it does fine.  I can't seem to get it to fail like it did that day.

Any thoughts?

Gundraw

Quoted: does it pass the short stroke test?

What is the short stroke test?  

The bolt seems to go back far enough to engage the bolt lock on the last round?  Is that it?  

However, I've tried everything to get the hammer to fall when I pull the trigger and hold, push the hammer back down onto the Disconnector (is that right??)  and then releasing the trigger and the hammer snapping forward and being caught, but not falling.  I've tried fast, slow, just feathering it out, and the hammer will never fall.

Gundraw