I bet the pin broke when he was firing 9mm, and he just didn't notice. The straps hold the pin in place, so it just continued to oscillate in the holes until it wallowed them out.

Quoted: Quoted: Quoted: I bet the pin broke when he was firing 9mm, and he just didn't notice. The straps hold the pin in place, so it just continued to oscillate in the holes until it wallowed them out. Interesting, but scary.  A stoppage might have saved the RR.  I would think this argues against the use of KNS pins.   Sam I would agree with this assessment.

And I would disagree: I broke a trigger pin on my M16A1 (back in '96, from use with an unramped 9mm bolt) and it also continued to fire, with the two stubs wobbling in place on each shot. If anything, the KNS pins would tend to hold the stubs more perpendicular to the receiver walls than a broken freestanding pin.

IMHO, this instead argues for paying more attention to how your M16 is functioning, particularly when using a 9mm or other non-design-native upper.

First, I can guarantee you that the broken pin affected ROF. Second, with a broken pin, the hammer or trigger/disconnector sit at an obviously wrong angle -- and when you push on them, they will "wiggle around" inside the receiver.

Then again, I'm one of those guys who doesn't wait for his car to break down before ever opening the hood.

Your buddy has my sympathies.

If it were me, I would send it to M60joe. I trust him most of the smiths now doing this work.

On how best to fix it:

--First, see if there is any chance he can just drill out the hammer-pin hole (and the hammer itself) to 0.170", the Colt commercial AR spec. That is the least "intrusive" way of handling it -- yes, you would have two pin sizes, but no one would notice.

--Next, if the hole is too enlarged to go to .170, I would use a bushing. The downside is that they are obvious (though the KNS locking pins, ahem, would cover the bushings). See the photos here: www.uzitalk.com/forums/showthread.php?t=19151

The advantages to bushings over welding up and redrilling: Well, you do not need to refinish the entire receiver, and preserving the original finish on a Colt is important for resale. More important, your receiver will be stronger: Colt used forged receivers because the tremendous pressure of the forging process lierally realigns the "grain" of the metal, increasing its strength. It is physically impossible to weld metal to the same strength, so the welded area will always be inherently weaker. In addition, you lose the anodized coating in the welded area.

--Rewelding and redrilling is a last-ditch approach. I'd then have entire receiver reanodized. This is best left for really trashed receivers, because no matter how nicely done, I've never seen a reanodize job that could pass for Colt's original. (In fact, the giveaway to a quality reanodizing like US Anodizing's work is that it's too nice to be Colt original.)

In any and all cases, if the rear trigger-pin hole is not damaged, I would not mess with it.

HTH.

Quoted: Gotta disagree with you on the KNS pins.  I have broken several trigger pins (including one SS one) and in every case one half of the broken pin has fallen out, causing the problem to be quickly discovered.  With the KNS pins holding things in place, the damage described above is all too possible.

It was a broken trigger pin that kept firing while wobbling and did not fall out that led me to KNS pins in the first place.

Quoted: Quoted: Quoted: Quoted: I bet the pin broke when he was firing 9mm, and he just didn't notice. The straps hold the pin in place, so it just continued to oscillate in the holes until it wallowed them out. Interesting, but scary.  A stoppage might have saved the RR.  I would think this argues against the use of KNS pins.   Sam I would agree with this assessment. And I would disagree: I broke a trigger pin on my M16A1 (back in '96, from use with an unramped 9mm bolt) and it also continued to fire, with the two stubs wobbling in place on each shot.

I would argue it means do not run your RR outside of its designed configuration - 5.56mm. 99% of all breakage I have seen involves shooting something other than 5.56mm MILSPEC. Running it in a caliber it was not designed for is just asking for trouble.  If you want to run these non-standard calibers, use an RDIAS and a replaceable receiver.