I have a colt preban ar15. It was working fine until I did some upgrades. I installed a non-rotating pin on the trigger, and installed a new 6 position collapsable stock. When I reassembled the rifle, the bolt carrier wouldn't lock in. It gets stuck halfway in the middle of the ejector port. The funny thing is that any other BCG I use works just fine. Also, if I put the colt BCG in another rifle, it works just fine to. It's like the factory bolt doesn't like the factory riffle anymore. Really strange. I've tried new buffer tubes, springs, gas rings....nothing seems to correct it. I'm completely baffled. Has anyone got a clue as to why this would happen? I could always just use a new BCG but I'd rather keep my factory colt BCG in my factory colt AR15.

make sure you installed the FCG correctly.

Does the buffer move freely over its full travel in the buffer tube?

Did you change the firing pin? If it is an sp1 style carrier and a m16 style firing pin is installed it can hang on the hammer notch when you try to cycle the action.

I didn't change the firing pin. The buffer travels fine. As I said, if I use the colt BCG in another ar15 it works fine. If I insert a different BCG in my colt rifle it workd fine. .?? I don't get it. I'm not sure what the FCG is? The trigger is the original, I just installed a non rotating pin system in so the pins should be the same diameter. Any one else have any ideas?

Again, here are two different size trigger and hammer pin sizes, being either .154" mil spec, and the larger non mil spec .170" that colt used in their early semi auto rifles.


So on that note, double check to make sure that the new pins you installed, are the same diameter as the pins that you took out of the rifle.  If you did install a .154 pin in a receiver/trigger that required a .170" pin, the size difference will cause all kinds of problem due to slop of the pin to receiver and part channel, being one of them the hammer not being retained low enough (disconnector not working correctly another as well).

FCG is fire control group. is the bolt carrier that works different that

the original carrier. I mean is the original an auto carrier and the

one that works a semi carrier..



How about posting some pics.

I'll try to post some pics. If your asking if it's a fully automatic BCG I'm not sure but I would think not. I know for sure the colt is not an automatic carrier.

Make sure to show pics of the buffer spring retainer area.

Try it without the non-rotating pin on the trigger.

When you put the none rotating pins in did you remove one pin and immediately put the new pin in or did you remove trigger or hammer assembly? Try removing BCG from upper receiver and using it to depress into buffer tube to see if it hangs up or moves freely.

How about putting the original pins back in and see if proper function returns.

So from a quick read your bcg gets stuck halfway...  can u slide it foreword and back with your upper detached from the lower?  Could you have somehow accidentally jarred the gas tube or key..??  Try your original parts as well... and I've seen the buffer retaining pin sticking to far up and catching the bcg... check for rubbing or scratch marks on the underside.