What is the approximate year that the above happened? Perhaps a definite serial number range? Is it definite or have examples of large pin models come up after it was thought they’d all gone to small pin?
Are the large pin models generally looked down upon now that the small pin versions exist as far as used sales?
Thank you for any info,
Scott
Circa 2008 if memory serves me correctly, it was around the release of the 6940.
my Oct 2008 Colt still have large pins but it’s a Match Target model… I think they started using milspec pins in early/mid 2009
Somewhere around LEO58000 range (I have a couple in that range and they are small pin). There was mixed manufacture between LEO56000 and LEO58000 as old stock was used up. I don’t know if there is an exact cut off date.
I would say that to be safe anything LEO60000+ should definitely be safe.
Some people who have the older large pin models might actually prefer the large pin to keep commonality of spare parts.
Actually the transition started much earlier, a GunBroker vendor verified for me a batch in the 48,xxx with small pins when the 6940 was released.
Thank you all for the replies, the info is most helpful.
Mine is in that range. Is there a way to tell by inspection, without directly comparing to another carbine?
Not without a micrometer or a pair of calipers.
The difference is only around .020".
Use vernier calipers
the firing pin trick is a quick way to tell 
a firing pin will fit just right in a small pin hammer hole
the pic below is not mine…I stole it from TOS
If you don’t keep a set of calipers around, use a ruler - the standard pins are just under 3/16" and the old Colt pins are right on 3/16". Not exact but I believe it will get you in the ballpark.