Any more ideas on how far back you would have to go for the changeover to the .154 pins. I have a 6920 LE046XXX, am I out of luck with the bigger pins. I called Colt customer service and they said they kept no records on when the switched over serial number wise. Any help appreciated. Thanks x_ra_y@yahoo.com
Please explain why you are out of luck with the .170" pins? 
The change to standard .154" pins was just made within the past few months after the 6940 came out.
As an fyi, I just got an mt6400c and it has .169 pins. As another fyi, there is a date on the barrel of 05/09. I just bought the rifle about a week ago and it wasn’t sitting on the shelf for months. I ordered it and it came in from a distributor.