My hammer was catching on the bolt when closing and I filed the lip just a tad as someone suggested.Unfortunately I filed too much because it will occasionally fire a burst(2-3rds).My question is can I just replace the hammer or do I have to replace the whole FCG to keep everything running smoothly?

If you had rolled filed the end that sticks up above the receiver and the portion that is catching carrier, then the hammer is should still be fine.  If you filed the part of the hammer that catchs the rigger sear, you will need to replace the hammer.

If you filed the hammer at the correct location (top of firing pin contact pad), then the hammer is fine, it's the disconnet that is having problems, and may be the only part that needs to be tuned/tweaked.

Let us know if you only lower the top edge of the hammer or killed the hammer by filing on the sear points.

my hammer looks like the one in this pic [url]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=12467&iGalleryUnq=934&iImageUnq=16143[/url]

The little ledge was catching on the bolt carrier and I rounded it just slightly.I'm guessing this is why it shoots in bursts sometimes but I'm not sure because I haven't fired the rifle bore filing it.

Since you didn't file the sear at the trigger to hammer contact point, there is hope yet.

Start off by shotgun the action open, hold the trigger all the way back and cock the hammer by hand to be retained by the disconnector.  The disconnector should retain the hammer.

Now very slowly release the trigger, the hammer should be released from the disconnector, and the trigger sear should retain the hammer.  Also, the hammer should be released from the disconnector just before the trigger comes back to rest.

If the rifle past this test, next is to close the action, then lock the bolt back, hold the trigger back and then hit the bolt release button. The bolt will slam home and the hammer should still retained by the disconnector since the trigger has the disconnector cam’d forward.

If the rifle fails either one of these tests, look at the position of the disconnector spring. The large end of the spring should be wedged into the slot of the hammer, not with the large side up against the bottom of the disconnector.

Chances are that either the disconnector spring is installed wrong, or the disconnector may need to be timed.  Lets just function test the FCG, then work from there.

Ok, I tried the test and it failed.I took out the disconnector spring and it looked like a cut down pen spring.Both ends were equal width but I replaced it with a new disconnector spring with the large end facing into the trigger.I performed the test again and it worked.I closed up the action and locked the bolt back.Pulled back the hammer and released the bolt.When I let off of the trigger just a little, the hammer let go.I think this failed the test.

With the rifle closed, lock the bolt back.  Then hold the trigger all the way back, and let the carrier slam home.  The disconnector, since the trigger is held back, should hold the hammer when the carrier slams forward.

If the hammer is retained, then slowly release the trigger.  The hammer should be released from the disconnector and caught by the trigger front sear just before the trigger comes back to rest (all the way forward).  

It is failing this test, pull the FCG parts and make sure that they are installed correctly and the contact sears of the hammer, trigger, and disconnector are still intact with no burs or broken edges.  Also, looks for signs of someone who may have tried to perform a home made trigger job.  Once you have reinstalled the cleaned, lubed parts, re-test.  

Bottom line is that the disconnector may just need to be tuned (takes about 3 minutes), but I just want to make sure that everything else in the FCG is working and installed correctly before we tune it.

Dremils and FCG parts are a very bad thing.

Pull the FCG parts and replace all the drimeled parts.  Even if you get the disconnector tweaked, when the parts where ground down, the case hardening was also removed. So the FCG will be out of spec/tune if a very short time.

Granted that I could save the parts for you, but it wouldn't happen for a few months.  The parts need to fitted, then re-cased harden.  It requires a mill and a furnace to do correctly.  At $50 for a new stock FCG, it's just a lot faster/ simpler to replace the whole group.

Granted that I will work over a FCG to get it to break at 4 lbs crisp with no over travel or creep, I am guessing that you are not set up to do the smithing or the time (read years) to ruin enough FCG to get it down to a science/art.

P.S.  Now would be a great time to upgrade to a two -stage trigger.  The RRA type goes for around $100 and a Jewel for a $175

Thanks Dano for all your help.I figured I'd need a new FCG.When I looked at the disconnector, it looked like it was cut with a cookie cutter.

Best bet is to go with a Bushmaster, J&T, or a Colt (correct size pins).  Some of the others on the market (read cheap) are produced with the wrong geometry between the hammer to trigger sear (the sear on the trigger is shorter, and causes the hammer sit to high at catch.  This is the reason that some hammers need to have the contact pad lowered, while other don't need the top filed to work.

Bottom line is to just spend the extra few dollars, and leave the fitting of drop in parts to someone else.