Figured I'd put this out there.  In another thread a few members and I discussed the theory that XM16E1s WERE marked with serial numbers consecutively, however due to a few manufacturing peculiarities with the unmilled lowers SOME were full fence, some were partial fence, and a few M16A1s got mixed in.  I'm trying to put together a ROUGH date range for when a given XM16E1 was manufactured, based on serial number.  I have collected close to 50 serials from demils that pop up from time to time, as well as the fence type, in an effort to see how many of these old workhorses (or their pieces) are still out there after 50+ years of hard service.  Believe it or not, that small amount has given me a really good idea of serial ranges for XM16E1s.  
According to The Black Rifle, there were only two contracts between Colt and the Gov that would involve XM16E1s, one from approx. 1-1964 to 12-1965 and one from approx. 6-1966 to ?  The appearance of full fence XM16E1s SEEMS to coincide with the start of the second contract I believe serial ranges will reflect this.
With the data I've gathered, I have noticed a few areas where I NEED more info to establish more solid dates.  That's where I'm hoping you guys can come in.  I'm looking for the following serial and fence data from any demils  you might have or have pics of:
- Full Fence XM16E1's earlier than 565155
- XM16E1s later than 713529
- XM16E1s between 508705 and 554748
- XM16E1s before 115505
-M16A1s before 605,000
- 604s approx. 509000-554000

I know its a weird request, but I plan to share the range info with the group (NOT the serials, for privacy sake above all else.)  Also, for privacy sake, I'm not even asking for pictures of them.  A simple "Hey, XM16E1 Ser#503949 has a partial fence" is great and more than perfect for what I need.  Please feel free to PM me ANY info you may have.  With the amount of rewelds out there these days, I don't want to get too personal.
I also want to make it clear that I do not wish to step on anyone's toes with this endeavor.  I value the time and efforts those like Ekie have put into this topic and I have used A LOT of the info already out there to help with my project.  I'm hoping to take their data and bring it to another level!

Please don't ever feel you need to apologize for "stepping on toes". Your quest for knowledge is admirable! And wanting to share what you find, THAT is what the retro forum is all about and I personally hope folks continue the study of these rifles forever.

I'll get ahold of my Buddy who has an XM16E1 demill that has, IIRC an X suffix after the sn and ask what the sn is and which fence it has. Off hand, I think it's a 5xx,xxx one.
I'll also shoot an email to a member who doesn't come around anymore who has a real deal XM16E1 and ask for the same.
I wish you the best of luck in your quest, and kudos for doing it!!!!
ETA, you may want to add for folks to also include if their fence has the small oil hole for the pivot pin spring/detent in their fence too just to see if an end date of use can be determined.

Admirable. Maybe you can prove me wrong but everything I’ve seen and read in addition to the rifles I have studied alludes to the fact that rifles were made with non-consecutive serials. Look at SAWS contract rifles, for example.

Thank you for your kind words.  My retro rifle is my favorite and was my dream rifle (Till I acquired it, but it still feels like a dream when I look at it, lol.).  I just wanna help the community!

I will full-heartedly agree, it might just be a theory, but it DOES kind of make sense once explained.  We won't know for sure until Colt comes out with info, or the military releases data relating to when rifles were received.

604 w/308XXX serial I have seen has full fence and no pin hole for the early buffer tube

There are Colt forms that talk about this, just FYI

Do you happen to have a link or two, if they are on the internet of course.  I'd love to read them!  Thought I'd combed things over pretty well here, but maybe I missed a thread somewhere.  
Anything to learn more!

One of a few:
Attached File


Again, if you look at SAWS contract rifles and compare them to the serials to their left and right, it’s pretty easy to see how they were not run consecutively. The 601 and 602s had serials to the left and right and most SAWS weapons were partial fence, etc and made in 1965 based on what I have read for the the contract. We know 601s were made 1959-1963 and 602s 1963-1964.

Here’s a couple oddballs you can add to your list...

SN 050000
US Property marked XM16E1 with NO FENCE this is a gold plated presentation rifle and most likely the first or second rifle marked as XM16E1 (personally I think it’s the first one given how the roll marks are made and the lack of a fence)

SN COS USA 1
US Property marked XM16E1 with Partial fence gold plated presentation rifle for the Army’s chief of staff like the above one mentioned it’s either the first or second rifle marked XM16E1 (i personally think this is the second one going off of how the roll marks look)

So that had to be made in 67

That’s something I’ve never seen a full fence 604

From my research, it COULD be as early as from one of the first batches of full fence lowers in mid to late 66 as well, if my theory that the start of full fence production sporadically began shortly after the start of the second contract of XM16E1s.  A rarity to be sure.  Maybe a box of blanks was sent to the wrong line and they sent it?  Anything is possible with Colt, lol.

It has to be December of 66 or through 67 to not have the roll pin hole for the buffer tube

I was going through my photos and I have a photo of both sides of the magwell of XM16E1 SN 562706 and this one has a FULL fence on it.

Interesting, thats the earliest serial I've seen for a full fence XM.  Very cool!  Thank you for looking!

601 Mfg'd  1959-1963Flatside
602- Mfg'd        1963 - 1964 Majority to AFFlatside
603/E1 Mfg'd    1964 - 1967XM16E1 Lower
603/A1  Mfg'd   1967 - 1982A1 Lower
604  Mfg'd       1964 - 1967,  1970XM16E1 Lower  1964-5 Upper has thinner arrow
605- Mfg'd 1965XM16E1 Lower Receiver
607 Slabside or Fwd Assist UpperXM16E1 Lower Receiver
609 1966-1967 w/ Fwd AssistLate 1966- early 1967 XM16E1 Rec- Late A1 Receiver
610 Slabside UpperLate 1966- early 1967
XM177E2 Mfg'd  1967-1970A1 Lower
651/652  Mfg'd 1970-1974?A1 Lower
653/653 No F/A  1971 - 1984A1 Lower
723 1980'sA2 Lower

No problem here’s a couple photos of it...

So the 300k 604 full fence no buffer detent hole really messed up my timeline for 604’s.

I don’t know if I have seen this discussed before but the 66-67 buffer tubes use a smaller wrench than the modern ones. I just handled/built 4 kits from the Puerto Rico Hwy patrol that had 65-66 features.

xm16e1 Full Fence 737187

Thanks!  This is the latest one in my list, so it could be one of the last!