I had this posted in the pistol caliber section and didn't receive many responses so I thought I'd move it here.
I just took my new 9mm, new to me that is, all factory Colt out for a test run. No problems feeding and digesting 3 different types of ammo, in two different magazines. There were few occasions when the rifle fired a 2 or 3 round burst when the trigger was pulled once. I tried to replicate the occourance by using different trigger pulls and such, but it seemed to occour randomly. I cleaned the weapon before taking it out, and this occoured after about 175 rounds went through the gun. I fired a total of about 300 rounds last night and this occoured maybe 3-4 times. While it was sorta cool, I'm concerned of any impending problem. Any ideas?
Thanks,
Tony

sounds like worn parts to me.  the thing about accidently going auto is it might happen when your not expecting it to, and you might lose control of the weapon.  probably won't happen, but it could, and that makes it unsafe.  i would replace fire control parts.

How dirty is the FCG?  I knew of a range rental 9mm that would burst when it got very dirty.  After it was cleaned, it'd fire normally for thousands of rounds until it got dirty again.

After the rifle was purchased, the entire rifle was cleaned very well with special attention paid to the BCG as well as fire control group.  I dissassembled the BCG once again when I got it home and it wasn't that bad.  There are no broken parts in the lower receiver, as was suggested to me.  One of the other members suggested a test to see if the disconnector is worn and that's fine too.
BTW, thanks for the help guys.

Hmmm.  Could it be occasional underpowered ammo not fully cycling the bolt to where the hammer is caught?

Are the 9mm AR's direct blowback, or do they have some other kind of cycling operation?

FYI-

BATF Abuses From the 70s

GOA Defends Pennsylvania State Trooper
Gun Owners of America takes on individual cases, depending on the situation.

GOA successfully defended a Pennsylvania State Trooper, in the last 4 years, against absurd BATF claims of "illegal possession of a machinegun".

The police officer consulted with BATF in reference to sending his legally-owned AR-15 back to Colt, because the rifle "doubled" from time to time. (Doubling is when a firearm fires two shots with one operation of the trigger; it indicates wear in the trigger group and/or disconnector.)

Following BATF's advice, the officer shipped it to Colt. BATF intercepted the package, tested the rifle until it fired two shots as a result of one operation of the trigger and then arrested the officer for "illegal possession of an unregistered machinegun".

GOA members provided money to get a legal team on the case; once again, a Federal judge threw a BATF case out with prejudice and lectured the Federal officials from the bench on the gross inappropriateness of their behavior.

Direct blowback.  Some of the rounds I was using were +P's but I didn't take notice of when the lower power ammo was used.  Perhaps that's it?

Well I guess that's good news Bend.  Perhaps a new FCG as the other guys suggested.