Yesterday was the third range trip for my 9mm AR but the lower used to sport a PSA Premium 5.56 upper so it actually has maybe 750 rounds on it.  9mm upper is PSA.  Lower is Anderson with a Spikes conversion block.  9mm buffer, spring and spacer.  Most of the lower parts came from my parts bin and from the EE.  Never needed to order a kit.  The 9 mil has never had a hiccup.  I did have do a little filing on the bolt stop to get the LRBHO to work but that's the only adjustment I've had to make.

I was wiping it down after a good cleaning today and noticed the open hole on the right side of the lower where the hammer pin should be.  The pin was in the other side and hammer was still working.  I replaced the pin.  Anyone ever had this happen before?  I don't even know when it happened.  The gun just kept on running.  Shot 200 rounds.  Could it have been just a bad pin?

Although it hasn't happen to me (used a JP anti-walk set), it is not rare.  Blowback action with a heavy bolt resetting the hammer stresses the hammer pin much more than an AR15 DI or piston action.

Pretty sure a ramped bolt will help reduce that problem

I've been running my 9mm AR since 1998 and never an issue. This was before the days of ramp bolts. I just had a dedicated 9mm hammer and whatever milspec trigger & and hammer pins.  I am sure I had over 10k rds on it.

I was ignorant to all the broken hammer/trigger pins until I joined this site. Kept reading about it, but I personally never had an issue. This site even convinced me into buying those KNS pins. Used the KNS pins a few thousand rds the pulled them because they looked silly.

Around 2011 I bought a DDLES/QC10 dedicated 9mm lower and rebuilt my 9mm. Got the bolt ramped and installed a Geissele G2S. I think I might have over 5k rds on this set up and no issue with broken pins. And I do more rapid fire with the G2S too.

I say broken trigger pins are rare. I would repace it with some stainless steel ones or ones from a reputable company.

I am a firm beliver in quality milspec lower parts kit (usually the pricy ones) vs bargin milspec parts kits (cheap ones).

The only failure I have experienced is a broken firing pin. Thats pretty impressive for almost 20 years. Dam I am getting old.

Its very common on Colts. Some people opine that you can ramp the bolt and it helps...and I'm sure it helps a bit, but the only cure is to replace the pin every thousand rounds or so.

Common enough that Colt switched to stainless steel pins on their 9mm offerings years ago. Not terribly frequent, though.

Thanks guys.  Forgot to say that my bolt is a PSA that came with the upper.  Supposed to be cut correctly to run with either the Colt system or Glock mags.  I assume this means it's ramped correctly. Never broke a pin on my Colt AR.  Granted it's not 9mm but I've been shooting it for 10 years.  I'll look on the EE for a better set of pins and maybe check into getter either a set of JP or KNS pins.

I had it happen.  Gun started doubling one day, tripled, and then emptied the entire mag before the pin completely separated.  This was an Olympic Arms complete rifle. 

After I broke the second hammer pin I replaced them with KNS, no problems since.

I have a couple DDLES (pre QC10) lowers with ramped bolts that I use in competition.  

Many, many, thousands of not-light rounds fired.