Recently while shooting my M16 with a 10.5" upper I had two malfunctions I'm still trying to figure out. I was having feeding issues, so I was firing it in semi. Both times I pulled the trigger in semi nothing happened. Then when I moved the selector switch to auto without my finger on the trigger, it fired 3-5 rounds on auto. It runs fine with my Shrike upper, but I'm a bit concerned with it going off unsolicited like that. I'm thinking of just tropping in a new fire control group, but want to verify that's what I should do with folks who know more than just how to pull the trigger like me.

take it to a gun smith that has worked on FA  AR's ....

I would agree it's probably a FCG issue. Replace it with a geissle SSF and if it's still doing it take it to a gun smith.

Who is the manufacturer of the M16? Or colt, Olympic, etc...

It's a factory Colt gun.

Ok, well assuming there has been no major damage or repairs to the lower I would say that if it's a colt it's def not a issue with the lower as they are the considered the gold standard when it comes to tolerances and specs of the pin hole locations and other mechanical features. Likely a worn out FCG, replace that and toss in s brand new mil spec m16 BCG and I bet the issue goes away.

If your running kns pins and one of the pins is broken.it can have issue like any other broken fcg pin, but it may not be as noticeable as the standard pins.
If not broken pins I suspect a worn or out of a spec fcg  or possible worn or improperly installed disconnector  spring.


Be careful..it is a dangerous situation

Replace the FCG with factory Colt parts. If you have KNS pins, rip that worthless shit out of there.

This +1 except for KNS pins being POS. Just remove them and replace with regular pins and NIB FCG (including sear) while diagnosing the issue.

are they really that bad?

I don't think so.  I'm not an advocate of KNS pins, but they aren't that bad.  I can understand guys with transferrables being worried about egging the pin holes over thousands of rounds and using them.



Personally I have a set of 1555 pins that I used to tighten up a loose trigger, I have another set in my 50 BMG after I saw a similar model KB and there was speculation it was caused by the hammer pin walking allowing the hammer to drop before the bolt was fully closed.



For most people they are a waste of money though.  They also have issues with Geissele triggers and I would avoid using them together.

No, they are great. Just yank them out while you are trying to diagnose your problem. They can cover up things like egged hammer holes, etc.

KNS M16 pin user here.....I see no downside to using them.

I guess I'm old school now.....although, my Shrike runs perfectly so maybe thats the secret.

I believe the bad reputation was with original gen 1 "dogbone" variant of the KNS anti-rotation pins which had a hammer pin which was hollow and which attached to the trigger pin via threaded screws.  On the Gen 1 setup the hammer pin also had oil holes which were problematic.  Specifically the hollow hammer pin would break where the oil holes were located, especially if used on 9MM.

The current "2nd" generation (and by current have been around for probably close to 10 years) the hammer pin is solid with no oil holes and has  "tabs" on the side so there is no screws tapped into it.   I am still not sure why they put the anti-walk detent in the center of the hammer pin since that is almost invariably where hammer pins break and the anti-walk detent is pointless on a KNS anti-rotation pin since they cant walk.  Why put a detent weak spot on the pin if it doesn't buy you anything is beyond me.  However, the solid KNS hammer pin is technically no weaker than a factory stainless pin but could be stronger if the spring detent in the middle was removed since its not needed.

The trigger pin on the Gen2 is still is hollow, has the oil holes and the "legs" are held on via screws to the trigger pin. I have never heard of a KNS trigger pin breaking and if it did it would be immediately obvious to the shooter as the trigger would wobble even with the legs still attached.

I have had a set of the second generation KNS pins with the solid hammer pin on a RR for probably 7 years or more  and have never had any issues.

Only hammer pins I have ever broken were on a 9MM setup using standard  (non-stainless) pins.  Upgraded to OEM Colt Stainless pins on my 9MM rig and have never broken them over many years of shooting.

I bet you have a broken trigger pin or a primer in the fire control group.

Sorry for taking so long to respond on here, there's been many shinny objects distracting me lately.

No, I'm not running a KNS pin, it's all factory.

Should I drop the ~$130 for a whole new FCG, or should I try a new trigger pin first. Also is there anything I can check visually to see what's wrong without pulling all the parts out?