Detailing parts variation of the following Colt models:

653
Commonly referred to as a M16A1 Carbine, slang as "CAR-15", nine million serial number range, 1971-1984?

723
Commonly referred to as a M16A2 Carbine, slang as "CAR-15", or "M4", 8 million serial number range,  1984-?

727
Commonly referred to as a M16A2 Government Carbine, slang as a "M4", 8 million serial number range, 1988-1993

733
Commonly referred to as a "Commando", 8 million serial number range 1984-1993?

920
USGI M4 Carbine, W serial number prefix, 1994-current

921
USGI M4A1 Carbine, W serial number prefix, 1994-current

921HB
USGI M4A1 Carbine with heavy barrel, W prefix serial number, deliveries beginning as early as January of 2001, to current.

I choose these models in that they are the most common Carbines delivered to the US Military from the 1970's and on (with the possible exception of the MK18).  Keep in mind that Colt used up quite a supply of 600 series parts on early 700 series Carbines.  For example, just because a 723 should have a delta handguard ring don't mean that it will, because quite a few were sent out from the factory with the older slip ring.

Just did barrel and buttstock parts, will get to the rest later............

Bird cage flash suppressor used on the 600 series:



A2 flash suppressor used on the 700 and 900 series:



Early lock washer on left, as used on the 600 series. Middle is the A2 peel washers used to time the A2 flash suppressor to TDC on the 700 series, and early M4/A1’s. Right is the current crush washer used on the M4/A1 starting in 2000:



Early 653 barrels were marked C MP B and are 1/12. The C means Colt’s, the M means Magnetic particle inspected, the P for Proof fired, and the B for chrome Bore:



Starting in 1974 653 chrome bores were marked C MP CHROME BORE. This marking was also used on early 1/7 twist 723's barrels:



Early on 723 barrel markings were changed from that used on the prior 653.  The C MP marking means the same as before. The NATO 1/7 specifies the rifle is designed for NATO standard ammo rather then M193 as used with the 653 (photo by YardDogOne):



733 barrel markings, the CB meaning Chrome Bore:



727 barrels have the same codes as M16A2 barrels, but are in two rows, and the C is in parenthesis (Note that some 723's use the same barrel as the 727):



M4/A1 barrels are marked similar to 727 barrels:



Starting as early as 1989 a single or two digit code by the front sight base is used, this one marked 56. Not sure of the meaning, maybe a lot code?



Early 727 barrels, as in 1988 had a star stamped near the chamber, meaning unkown:



As early as 1989 an O is stamped by the chamber (some look like C’s) were the star was previously, indicating a chromed chamber/bore:



Starting in 95 a date code is stamped by the front sight base all though barrels can be found with dates as early as 02/95 production continued well into 1995 with some barrels being dated and other not. First two digits is the month, second two digit number is the year, this one 03/02:



This one 11/00:



Beginning in the late 90’s a paint mark is added in front and under the barrel nut, not sure of it’s meaning (note that the barrel nut is impropery installed, seen quite a few like this since 1998, they don't work very well):



The .625" "C and Bell" front sight base was used on Colt Carbines from 1971 until the late 1980's.



"Crown" front sight base was used on some 700 series Colt Carbines in the Mid 1980's, this one on a early 723 barrel (photo by YardDogOne):



Very early 727 barrels also used a .750" "C and Bell" front sight base.



Typical gibberish front sight forge code, such codes have been used since the late 1980's:



The M4/A1 front sight base is similar to earlier front sight bases, except that the platform the sight post screws into is higher, these are marked with an F on the left side, and use a standard A2 front sight post.  The "F" front sight base went into production in 1995.  At least one large 1995 batch of flat top M4A1 Carbines were issued that did not have F front sight bases and used standard A2 front sight post.  



Soon after working on carbine versions of the M16A2 Colt found that M855 fed low due to various reasons.  To maintain reliable feeding the feeding ramps in the barrel extension were lowered into the upper receiver.

Left, M4 feed ramp used on the M4/M4A1.  

Middle, extended 700 series Carbine feed ramps.  These are shallower then the feed ramps used on the M4/M4A1, date back to at least 1988, are commonly found on 727 and 733 Carbines, some later ones are even stamped "4".

Right, standard rifle feed ramps.  These feed ramps were used on 600 series Carbines, and can be found on 700 series Carbines as late as 1990:



Extended 700 series Carbine feed ramps cut into upper:



M4/A1 feed ramps cut into receiver:



Extended 700 series Carbine feed ramps, note the chrome on the inside of this 1988 727 barrel extension:



M4/A1 feed ramps, note extension marked “4”




600 and 700 seris Colt Carbines had riveted front swivels:



Early M4/A1 swivel was a pinned on type developed for use with the M16 series and the M203.  It was reversible so it could be used on both .625" and .750" barrels:



Late M4/A1 swivel, same as before but now .750" only, used in 2000 and on production:



Colt 653 used a standard slip ring:



Colt 700 series and later used the A2 delta ring:



Top barrel is standard profile as used on the M4 and early M4A1.  Lower barrel is the heavy barrel used on M4A1's, or Colt Model 921HBn as early as January of 2001:



The forward M203 cut out on 700 series Carbine and the M4/A1 are a bit different.  The angle slopping into the cut out is sharper 700 series Carbines.  Model 727 on top, and M4/A1 on bottom:



Handguards, 600 and 700 seris on left, early M4/A1 in the middle, and late M4/A1 on the right.  Early M4/A1 handguards are double heat shield, and late (1999 on) M4/A1 handguards have glued in double heatshields and are more matte.






Front sight post used on the 600 series Carbines was the same as that used on the M16A1 except it is about .040" taller:



Front sight post used on 700 seris Carbines are the same as that used on the M16A2, save it is about .040" taller"



Front sight post used on the M4/A1 is that same as that used on the M16A2:



600 and 700 series Colt Carbine buffer on the left.  On the right the "H" buffer used on the M4/A1 (note the flats on the sides of the "H" buffer).



The "H" buffer's pad is pinned on:



600 and 700 series Colt Carbine 2 position receiver extension on bottom, M4/A1 four position receiver extension at top:



600 and 700 series Colt Carbine castle nut on left, M4/A1 castle nut on right:



Top, 600 series aluminum Colt Carbine buttstock, used from about 1967 until the mid 1980's.

Middle, buttstock used from the mid 1980's up through 2002.

Bottom, modern Colt buttstock used since 2002:



Buttstock pictured in the middle are typically marked with a raised "N":

Thanks...another  outstanding  post!

nice

gotta tag this one for reference

Well, Holiday is over, looks like later in the week before I finish this one up......

Thanks for all pics and descriptions Ekie

My 1994 M4 upper has an F stamped FSB with no date code.

This is a factory 723 picture:



Project 723

Quoted: My 1994 M4 upper has an F stamped FSB with no date code.

First thought is long transition time on date codes (as in barrels made in 1995 that lack date codes).........., second thought is I don't think there were any flat tops M4 Carbines issued in 1994, being that RIA did not standardized the flat top till 1995?

We had this discussion before, will have to look that up, hope to have time to work on this tonight....

Wow, nice work and great pictures.

What is incorrect about that the barrel nut on that painted upper?

Also the leaf spring from the RAS goes under the handguard cap. (wink wink)

I remember that discussion.  I think we concluded it was from 1994 but I'm not sure as I deleted it.

We could say it is from 1995 as old parts could still be used up.

Very Nice!  Thanks!

Great reference post...Thanks!

921HB (USGI M4A1 Carbine with heavy barrel) I can't remember when they started making these, need to look it up
=========================

Production took effect in 2001.

Hotgun

I found it here:

ar15.com/forums/topic.html?b=3&f=123&t=267251&page=5

Quoted: I remember that discussion.  I think we concluded it was from 1994 but I'm not sure as I deleted it. We could say it is from 1995 as old parts could still be used up.

Quoted: Quoted: My early M4 upper has a F marked FSB and a barrel with one of those codes (not date) by the handguard cap. It has a "4" above the gas tube hole. I will get pics of it later this week. I can think of three explanations for this.  One being a transition time, where both parts are used.  Not at all uncommon from what I have seen on Colt's US Service rifles.  Actually, long transitions times is the norm. The other being your upper is commercial and Colt's moved to the "F" FSB prior to RIA approving the change.  Again, this is also common, for example the flat top upper was put into production in 1992, but not standardized until 1995.  I lean more to your upper being commercial and thus different.  That being have never seen a USGI upper marked "4", and early TM's show the marking as "M4". Third explanation is that the timeline went like this: 1994 O stamp added to barrel 1995 F stamp added to FSB (say this started in the Summer) two digit code changed to date code (lets say this started in the Fall) Lets say that is the case, then we could go with Bill Davis's uppers being a batch from the Spring of 1995, and yours from the Summer of 1995.

Quoted: Quoted: 1994 O stamp added to barrel 1995 F stamp added to FSB (say this started in the Summer) two digit code changed to date code (lets say this started in the Fall) Lets say that is the case, then we could go with Bill Davis's uppers being a batch from the Spring of 1995, and yours from the Summer of 1995. Seems like a likely explination.

Couple of things we have learned since that discussion.  One being that there are barrels dated as early as 02/95 (it is in the 6520 data base).  Another being that the O stamp dates back as far as 1989.

Seems to me that the O stamp is not consistent, for example my 1993 6601 does not have a O stamp, at least I don't think it does, need to check it.

Time line does not add up that RIA approved the flat top in 1995, and Colt started stamping all barrels in Feb of 1995.  If that was the case then all factory original flat top uppered M4/A1's in DOD inventory would have barrel date codes, but they don't.

It must have taken a year or more for Colt to consistently date stamp their barrels.

Quoted: Wow, nice work and great pictures. What is incorrect about that the barrel nut on that painted upper? Also the leaf spring from the RAS goes under the handguard cap. (wink wink)

Barrel nut is overtimed past TDC so that one of the teeth is contacting the gas tube putting it in a bind with the carrier key.

Thanks for the heads up on the RAS, had not noticed that.  

ETA:

Come to think of it, may have done that because the upper had trouble with the gas tube binding on the key and causing feeding malfunctions.  The RAS don't help with that, really need to get a RIS on there, more appropriate with a SOCOM upper, and it don't touch the gas tube.

Quoted: 921HB (USGI M4A1 Carbine with heavy barrel) I can't remember when they started making these, need to look it up ========================= Production took effect in 2001. Hotgun

Rather then digging through stuff, here is the M4 timeline I tossed together with input from scottryan:

ar15.com/forums/topic.html?b=3&f=123&t=267251&page=4

Quoted: 1994 H buffer approved by RIA 1995 Colt's/Swan flat top upper was adopted (one batch delivered in 1994 with fixed handle) 1995 "F" raised front sight base platform 1996 US Government gets the M4 TDP from Colt's 1996 Crane releases the TDP to outfits like FNMI 1997-1999 all hell breaks loose with M4 TDP, FN sues; FN vs US for the right to get M4 contracts, they lose and Colt's ends up with a sole source contract for the M4 Carbine good through 2009, with 5%royalties through 2037. 1998 "T" markings on upper 1998? M4A1 offered with optional heavy barrel (SEALs blew up the skinny barrels on auto, they are not sub guns you know; Ekie's comments, no verifiable source) 1998?anodizing changed to black 2000 new side swivel 2000 flash hider peel washer changed to crush washer 2002 new buttstock 2002 roll mark changed to COLT DEFENSE 2002 stronger lower forging used 2003 RIA authorizes that the black extractor spring/buffer be replaced with the gold spring (some won't run without some extractor help, SOCOM even came up with a donut to help since RIA would not approve Colt's M4 extractor spring for years) 2003 M4A1 standard with heavy barrel 2004 Colt's begins development of a piston driven M4 type Carbine 2005 Colt's purchases Diemaco, a licensed producer of Colt's products 2005 Colt's licenses production to Turkey so that they can replace their G3's with M4 Carbines

What we do know is that Colt offered the RO921HB starting in 1998, and that there was a large shipment of RO921HB's shipped out in early 2001 to the various SFGs.  Note this box is dated January of 2001:



Also note the barrel date on the RO921HB in the first picture, that being 11/00.  I don't know that this shipment was the first one, but never heard of an earlier one.  Will go with production starting in 2000 and deliveries starting as early as Jan of 2001.

Another clue on the "F" FSB, Colt was producing this part as early as Feb. 1995:

Quoted: Paladin's current Zombie rifle was a neutered Colt MT6700 in a previous life.  I bought it NIB June 1995.  Per Colt's customer service representative, it was built Feb 1995. Colt Match Target Competition HBAR s/n CCH 0020XX "F" marked FSB.  right side of FSB marked "S", "RI in circle", and "2".  Non-chromelined 20 inch HBAR roll marked "C MP 5.56 NATO 1/9".  No flash hider, no bayonette lug. A close contender for "THE BEST RIFLE" I have ever owned, and it shot dime sized 100 yard groups right out of the box! Paladin

From the 6700 data base:

ar15.com/forums/topic.html?b=3&f=118&t=271181

I've got a 14.5 pencil barrel with a 1/7 twist (723?) no other markings such as a date code or "O" chrome vendors marking



Cant figure the front sight base though, no markings on the other side, any ideas on that

Quoted: I've got a 14.5 pencil barrel with a 1/7 twist (723?) no other markings such as a date code or "O" chrome vendors marking pic11.picturetrail.com/VOL366/498052/7712386/151700364.jpg Cant figure the front sight base though, no markings on the other side, any ideas on that pic11.picturetrail.com/VOL366/498052/7712386/151700330.jpg

The "crown" FSB looks familiar to me, but don't remember when they were used.  Will have to consult my digital photographic library, but don't have access to that till this weekend.

Will have to give Leid a heads up on this thread, he has an early 723...........

so what is the diff between a model 727 and a m4/a1.  I have seen stripped barrels with the (c) before.  

Quoted: so what is the diff between a model 727 and a m4/a1.  I have seen stripped barrels with the (c) before.

Well, quite a bit, but here are few items:

markings (lower roll markings, barrel markings, etc...)
front swivel
barrel profile
feed ramp angle
handguards
receiver extention
receiver extention nut
buffer
extactor spring
extractor buffer
date of manufacture
front sight post
front sight base

Hmm, come to think of it, might be easier to list the parts that are the same.

Excellent post

taggage

Quoted: Quoted: so what is the diff between a model 727 and a m4/a1.  I have seen stripped barrels with the (c) before.   Well, quite a bit, but here are few items: markings (lower roll markings, barrel markings, etc...) front swivel barrel profile feed ramp angle handguards receiver extention receiver extention nut buffer extactor spring extractor buffer date of manufacture front sight post front sight base Hmm, come to think of it, might be easier to list the parts that are the same.

So a 727 is a regular carbine with a steped barrel like a m4?  Right?
I have a (c) marked barrel and it has the m4 ramps.  The only difference I can tell in it and a m4 barrel is the ( ) around the C and the fsb isnt F stamped but it is the correct profile like the F stamped ones.  In your list why would the reciever extenion be different, a 727 is a carbine.  

Quoted: Quoted: Quoted: so what is the diff between a model 727 and a m4/a1.  I have seen stripped barrels with the (c) before.   Well, quite a bit, but here are few items: markings (lower roll markings, barrel markings, etc...) front swivel barrel profile feed ramp angle handguards receiver extention receiver extention nut buffer extactor spring extractor buffer date of manufacture front sight post front sight base Hmm, come to think of it, might be easier to list the parts that are the same. So a 727 is a regular carbine with a steped barrel like a m4?  Right? I have a (c) marked barrel and it has the m4 ramps.  The only difference I can tell in it and a m4 barrel is the ( ) around the C and the fsb isnt F stamped but it is the correct profile like the F stamped ones.  In your list why would the reciever extenion be different, a 727 is a carbine.

M4/A1 receiver extension is 4 position, Model 727 is two.

I just added more info and pics regarding feed ramps....

Quoted: pic11.picturetrail.com/VOL366/498052/7712386/151700364.jpg

I is it OK if I add that picture to the first post, with credit to you of course?  I don't have any 723 stuff.

Quoted: Quoted: pic11.picturetrail.com/VOL366/498052/7712386/151700364.jpg I is it OK if I add that picture to the first post, with credit to you of course?  I don't have any 723 stuff.

that'd be fine, dont worry about giving any credit

Updated, now has feed ramp and front sight post info.

Ekie,
     As always, very accurate info!
                                        Thanks,
                                         Carey

Quoted: I've got a 14.5 pencil barrel with a 1/7 twist (723?) no other markings such as a date code or "O" chrome vendors marking pic11.picturetrail.com/VOL366/498052/7712386/151700364.jpg Cant figure the front sight base though, no markings on the other side, any ideas on that pic11.picturetrail.com/VOL366/498052/7712386/151700330.jpg

Just noticed that yours has the old handguard cap.  And it does seem Colt was pretty good about stamping thier carbine barrels with the O stamp since 1989.  Colt began to move away from the C and Bell FSB during M16A2 production (about 83-87) so I would date your barrel to 84-87.  It has regular rifle feed ramps, right?

Quoted: Ekie,      As always, very accurate info!                                         Thanks,                                          Carey

Thanks, take it yours has the same front sight base as YardDogOne's, or is it the older "C and Bell"?

Quoted: ..... so I would date your barrel to 84-87.  It has regular rifle feed ramps, right?

Correct, NON - M4 ramps

Thanks for the info

Quoted: Quoted: ..... so I would date your barrel to 84-87.  It has regular rifle feed ramps, right? Correct, NON - M4 ramps Thanks for the info

Good to hear on the feed ramps, I would be real confused if it had extended ones.

Went ahead and updated the first post with info from you and Carey.

nice work, Ekie

Quoted: nice work, Ekie

Thanks, another Holiday, should get this updated.  Going to add other parts, such as buttstocks:



And will also include other models, such as the 733:

UPDATED.

I just found something interesting.  Just took a 733 upper apart to get a closer look at the feed ramps.  They are the 700 series extended Carbine ramps but the extention is marked 4.  These ramps do not match up with later M4 upper receivers in that they are shallower.

Quoted: I just found something interesting.  Just took a 733 upper apart to get a closer look at the feed ramps.  They are the 700 series extended Carbine ramps but the extension is marked 4.  These ramps do not match up with later M4 upper receivers in that they are shallower.

what year do you figure these were?

You think they were the precursor to the ramps we know today?

Quoted: Quoted: I just found something interesting.  Just took a 733 upper apart to get a closer look at the feed ramps.  They are the 700 series extended Carbine ramps but the extension is marked 4.  These ramps do not match up with later M4 upper receivers in that they are shallower. what year do you figure these were? You think they were the precursor to the ramps we know today?

The 733 uppers I have date 1989-1992.  Sorry, can't narrow it down any more then that.  The oldest upper I have with the 700 series Carbine ramps is about 1988.  It is not marked "4", and is pictured in the guide.

Yes, these are precursors to the later "real deal".

I'll get buffer tube pictures (not attached to a lower) of every variation including thread finish, if you want them.  I think we dicussed this before.

Quoted: I'll get buffer tube pictures (not attached to a lower) of every variation including thread finish, if you want them.  I think we dicussed this before.

That would be excellent, please do.

I'll try to get that done by tommorrow.

Great info, Thanks!