New info, so here is an update.  Some years are rounded off, for example the chrome chamber went into production in September of 1967, I round it off to 1968, same story with the chrome bore, introduced in Dec of 1971 and rounded off to 1972.

This guide is specific to factory original Colt 603 barreled uppers.  Colt delivered 603's to the US Army from the Spring of 1964 through 1982.  These were originally roll marked XM16E1 until early 1967 when the US Army type classfied the 603 as the the Standard A M16A1.

1964-1967
XM16E1-M16A1

Square forging transitioning to round starting in 1966
no forge code
black lugs
counter bored front lug
Colt proof marked
gray green anodizing
early port door transitioning to standard A1 port door in 1964
matching slip ring transitioning to purple slip rings in 1966
cast FSB transitioning to unmarked forged with no drain hole in 1964
drain hole added to FSB in early 1967
M VP 12 barrel transitioning to MP 12 in 1966
three prong flash suppressor transitioning to bird cage in 1967 (in US Army inventory three prongs were replaced with bird cages long ago)
carbon steel gas tube transitioning to SS with bend in front of slip ring
handguards have no drain holes in the heat shields



1968-1970
M16A1

round forging
no forge code
black lugs
counter bored front lug
Colt proof marked
gray/green or gray/blue anodizing
standard A1 port door
purple slip rings transitioning to black
un marked forged FSB with drain hole
MP C barrel transitioning to C MP C
bird cage flash suppressor
SS with bend in front of slip ring 1968, modern gas tube 1969
handguards have drain holes in the heat shields, and starting in 1969 the are marked L & R



1971
M16A1

round forging
no forge code
black or gray lugs
no counter bore on front pivot lug
Colt proof marked
gray/blue anodizing
standard A1 port door
matching slip ring
C and Bell FSB with flash milled off front and back
C MP C barrel
bird cage flash suppressor
modern gas tube
handguards have drain holes in the heat shields and are marked L & R



1972-1982
M16A1

round forging
forge code, CK used 1972-1973, CH used 1974-1982 (CM used in small number 1972-1973)
gray lugs
Colt proof marked
gray/blue anodizing
standard A1 port door
matching slip ring
FSB with forging flash front and back C and Bell marked
C MP B barrel transitioning to C MP CHROME BORE in 1974
bird cage flash suppressor
modern gas tube
handguards have drain holes in the heat shields and are marked L & R



Some details of a square forging used 1964-1967:





Some details of a round forging used 1966-1982:





No forge code 1964-1971:



CK forge code 1972-1973 (standard):



CM forge code 1972-1973 (alternate):



CH forge code 1974-1982:



Black counter bored front lug 1964-1971:



Gray front lug 1971-1982:



Colt C in square and VP in triangle proof marks:



Original port door phased out the first year of production in 1964:



Standard "A1" port door used 1964-1982:



Orignal cast FSB used for a short time in 1964:



Forged FSB used 1964-1970.  Drain hole for front sight post added in 1967 prior to the MP C barrel:



Transitional 1971 FSB.  Same as the later type, but flash machined off:


pic curtsey of mentalstampede

Late forged FSB, flash left on front and back, and marked with C and Bell, 1972-1982:



M VP 12 barrel used 1964-1965:





the M VP 12 barrel extension was also marked with a C



MP 12 barrel used 1966-1967:





MP C barrel used 1968:

Note the drain hole for front sight post:





MP C were also plated in the barrel extension:



C MP C barrel used 1969-1970:



Some 1969 CMPC barrels had chrome all the way out onto the locking lugs and part of the feed ramps. 1969 CMPC barrel on right, chrome chamber and bore barrel on left:



C MP B barrel used 1972-1973:



C MP CHROME BORE used 1974-1982:



Three prong 1964-1967:



Bird cage 1967-1982:



Original gas tubes were carbon steel and will attract a magnet. These were used on the XM16E1 for a short time before switching to stainless steel.  Note the bend is right infront of the slip ring assy:



Modern gas tube with bend further out, these were in use starting in 1969:



H&R and Hydramatic also made M16A1 rifles.  Numbers produced were much smaller then Colt, so these uppers do not turn up as often.  Both delivered M16A1 rifles from 1968 through 1971.  Some features to help ID these include:

no Colt proof marks in front of the port door
forging flash left on the front or rear of the carry handle (or both)
older upper without counter bore on front lug
MP marked upside down on the left side of barrel

Many rifles were rebuilt, especially Vietnam era rifles.  Typically the barrels were replaced.  Some examples of markings found on replacment barrels include:

SAK
FNMI
MFR26978
C MP CHROME BORE (also used as factory original)

Frequantly rebuilds were refinished either with with a thick black stoving, or a thin, smooth, gray solid film lubricant.

Beside the barrels other parts can be replaced during a rebuild.  Some examples of modern parts used in rebuilds:

high gloss black slip ring on a upper that should have a matching slip ring
big full round forward assist
LM forge code upper
replacement CH forge code upper without proof marks
upper with shell deflector
L & R marked handguards on an older upper
A2 port door
delta ring

Tack it.

Any info on the 605 model?

The 603 Buyers Guide thread has helped me a lot. Thank you for the update!

Originally Posted By RTUtah: Tack it.

What he said.

Does the forge code CM mean the upper was made under contract by Martin Marietta?

No, USGI keeps me busy enough.

Yes, a Martin Marietta forging for Colt.

Thanks Ekie, for taking the time to post all of that great info!!

Thank You Ekie.



"I Love the Retro Forum"

Great info. as always.  Let me once again ask the often asked but never answered question.  How can you tell the difference between a H&R and a GM upper?  Based on what I've seen I don't think there is any difference but I'm not sure about that.   Any thoughts?

This needs to be tacked.

What is the differnece between the earlier square forging and the later round forging?  How can I tell?  

ShaunN

Sweet!!!

I am in the final stages of my early XM16E1, & have a question. I just picked up a barrel w/a cast FSB, but it has a rubber coated & riveted sling swivel. Now I am positive this is not original, but want to know if the front sling swivel should be bare or rubber coated on a 64' vintage XM16E1. If it should be bare, what about the rear?

It has been my understanding that both swivels on a XM16E1 should be coated, but is that theory correct with a cast FSB?

Rubber coated would be correct front and rear.

Still no tack?

Not only tack it, but but it in big, bold, red letters with READ THIS FIRST in front of it...naw, wouldn't help.

Thanks Ekie - this really summarizes all the great info in your M16 guide. A great quick reference. TACK IT!

ETA: But don't put it in Forum resources - no one seems to see those even though they are at the top of the page. Like I said, the letters should be in red or yellow or something.

Thanks tgus.

Now all I need to do is knock this rivet out & get me a roll pin.

+1 this needs to be tacked.

I'm hoping these comments are not directed to me asking my question. Cause I did not see the answer here.

Yep, needs a tack.

Tack this, please.

ETA:  Thank you.

So I just purchased an A1 upper, NIW with a LM forge code.  I presume this is a good quality upper for a build?

Thanks

What do you call the M16 upper that is A1 in every way but has the burton button - M16A1E1 ?.  I ask as many years ago while in uniform one of these turned up in a couple racks of refurbished M16A1's in the arms room. Wound up with that upper and it's chrome bore barrel down the road.
 I think it's an A1E1 from some nomenclature I saw but not sure as I've never seen another one. I figured this was made around the time of product improvement to the M16A2 ?.
I can do pics  if requested .... well I tried, but this site does not do direct pic posting,sorry.

Posted the pics on Jouster :

http://www.milsurps.com/showthread.php?t=13029

Use photobucket to post here. Real easy. What kind of barrel does it have; markings etc. Is it 1/7 w/ A1 profile perhaps? If so then M16A1E1 is probably what ya got based on what I learned recently on another post. Rare bird and would make a very cool build.

Magnus ;  I posted pics on the link  - I don't use those photbucket or similar formats for pic hosting , just not my cup of tea.
 Anyhow it is stricly an A1 has the MP  with C marked barrel. I knew when I first saw it in the rack it was something 'special'. It's in very nice shape considering it was reconditioned before I acquired it. I've probably put only 4-5k rounds through it in the 15 years I've had it.

Sounds like a replacement C7 upper.
Take a look HERE.
Scroll down to Colt/Diemaco C7.
Some M16A1's had uppers replaced with C7s.

Just a bit of history, during the summer of 1987 we (1/5th SFGA) turned in our old XM16E1s for new M16A2s at Fort Campbell, Ky (Group HQ along with 2nd and 3rd Bns where still at Bragg).  One of these days when I'm home, I'll see if I have my old serial number.

CD

Nice thread... With lots of great info.

I'd like some history/information on the LM forge codes as well, if anyone knows?

I recently acquired a C H Forge marked A1 upper with out a forward assist can anyone give me some info ?

edit: this has a large front pin hole and no recess for the auto sear

Colt commercial SP1 civilian version. Uses a bushing to adapt to push pin lowers.

Please write a book on this, we could use a coffee table style book like this.
Version by version change by change, I have a book done on the VW Type 1 {Beetle} which does this, it sure helps at swap meets
and when you're a restoration.  I'm sure you could sell an entire printing to just the forum members, I know I'd be in for three copies.
Check out Schiffer Publishing they produce museum quality books like that.  Just check the three volume set on World War 2 German helmets
700 pages of color!

Thank you for the inspiration!

Please write a book on this, we could use a coffee table style book like this.
Version by version change by change, I have a book done on the VW Type 1 {Beetle} which does this, it sure helps at swap meets
and when you're a restoration.  I'm sure you could sell an entire printing to just the forum members, I know I'd be in for three copies.
Check out Schiffer Publishing they produce museum quality books like that.  Just check the three volume set on World War 2 German helmets
700 pages of color!

Thank you for the inspiration!

C K forging on what appears to be an H&R?