All, I decided to revamp @Ekie's USGI M16 Series Variation Guide because I have gotten tired of seeing all of the Photobucket watermarks over all of the pictures... Hopefully Imgur doesn't decide to screw us the way Photobucket did. I figured somebody should do it before the guide looks like the Carbine Variation Guide, where all of the pictures have completely disappeared. As such, the majority of this thread is thanks to Ekie back in 2005, but I do plan to make changes and edit info that has been learned in the 15 years since Version IV came out.

Here is the revamped version, with unmolested pictures:

Eventually the variation guide will cover much more, figured I could start with the flash suppressor and the butt stock screw, and add the other parts in between here and there, here is a start (not covering Navy rifles such as the M16A3, or Carbines).

Special thanks goes to WpnsMan his data base of early M16A1 and M16A2 rifles has been indispensable.

USGI SERIAL NUMBER DATA BASE (serial numbers listed in chronological rather then numerical order)

101-14,484
1959-1963
US Air Force/Project AGILE/SEAL issue Colt's AR-15 Model 601, roll marked ARMALITE.  Some sold commercially to police departments, small numbers to foreign militaries such as Malaya, India, Australia, Burma, and Singapore.

20,000-39,999
1963-1964
US Property marked AR-15 Colt's Model 02 issued to US Advisors in Vietnam, and US Air Force.  Few hundred commercial/export examples were made that lack US Property markings.

40,000-49,999
1964
US Property marked US Air Force M16 Colt's Model 604.

50,000-199,999
1964-1965
US Property marked US Air Force M16 Colt's Model 604 & US Army XM16E1 Colt's Model 603.

14,500-14,916
1965
Commercial/export CAR-15 series and US Property marked GX series for S.A.W.S. contract (note, CAR-15 refers to a family of Colt's weapons, not just short ones).

15,000-19,999
1965
Commercial/export CAR-15 series.

200,000-202,446
1965
Commercial/export CAR-15 series.

202,447-379,353
1965
US Property marked US Air Force M16 Colt's Model 604, and a few commercial export models.  There are also examples of commerical/export marked models using the 20X,XXX serial number range produced in the late 1960's.

400,000 series
1966-1973 or so
Only a few rifles/carbines made in this serial number range and known examples are spread out over several years of production.  Zero US Property marked rifles have been observed.  Highest know example is 418,XXX and dates from the early 1970’s.

500,001-749,999
1966-1967
US Property marked XM16E1 Colt's and M16A1, both Colt Model 603.  There are also a small number of US Air Force M16 Colt's Model 604 found in this serial number range.  Serial numbers in this range were not run in order.  M16A1’s have been observed with serial numbers as low as 604,505, and XM16E1’s have serial numbers as high as 741,12X.

750,000-752,443
1966
Experimental HBAR.

752,444-899,999
1967
US Property marked M16A1.

900,000 through 909,999
1966-1970
US Property marked Govt. Carbines.

910,000-919,999
US Property marked Colt's M16A1 and US Air Force M16 Colt's Model 604.

920,000-999,999
No known examples.

1,000,000-1,999,999
1968-1969
US Property marked Colt's M16A1

2,000,000-2,24X,XXX
1968-1971
US Property marked H&R M16A1.

3,000,000-3,469,217 (approximate)
1968-1971
US Property marked Hydramatic M16A1.

9,000,0000 series
1970’s & 1980’s
In general these are 1970’s and early 80’s “A1” type 600 series commercial/export marked weapons.  There are some exceptions, for example US Property marked Govt. Carbines.

AL prefix
1970
Lebanese contract rifles, some 14,000 made.

Note on 4,000,000 series Colt’s, there are quite a few commercial/export marked rifles/carbines mixed in.

4,000,001-4,060,000
1970
US Air Force M16 Colt Model 604.

4,060,001-4,221,800
1970
US Property marked M16A1.

4,221,801-4,285,400
1970
US Air Force M16 Colt Model 604.

4,285,401-4,521,000
1970
US Property marked M16A1.

4,521,001-4,521,850
1970
US Air Force M16 Colt Model 604.

4,521,851-4,638, 400
1970
US Property marked M16A1.

4,638,401-4,643,400
1971
Model 613 for Malaysia.

4,643,401-4,701,400
1971
US Property marked M16A1.

4,701,401-4,701,900
1971
Model 613 Commando

4,701,901-4,844,400
1971
US Property marked M16A1.

4,844,401-4,849,400
1972
Model 613 for Taiwan.

4,849,401-4,926,000
1972
US Property marked M16A1.

4,926,001-4,928,000
1972
Model 613 for Philippines.

4,928,000-4,936,400
1972
US Property marked M16A1.

5,000,000-5,4X,XXX (app)
1973-1982
US Property marked M16A1 Colt's Model 603 (not aware of any Air Force M16 Colt Model 604's with serial numbers this high).  Also some export/commercial models.

6,000,000-6,590,478 (approximate)
1983-1986
US Property marked M16A2 & US Property marked XM4 prototypes Colt's Model 720.

8,000,000 series
1980’s
In general these are 700 series commercial/export marked models of the M16A2.

7,000,000-7,429,766  (approximate)
1988-2003
US Property marked FN M16A2.  There are also Balimoy M16A1 lowers restamped A2 in this serial number range.  These were used as replacement parts by Anniston.

W prefix
1994-current
US Property marked Colt's M4/A1 Carbine, Colt's Model 920/921.

A prefix
1990’s on
900 series Commercial/export versions of the M4 Carbine.

10,000,000 serial number range
1997-
US Property marked Colt's/FN M16A4


photo by AmericanSheepDog

PARTS GUIDE:

ArmaLite “duck bill” flash suppressor, this part was beefed up almost immediately after the AR-15 went into service, and was only used on the Model 01 AR-15. Apparently the tongs busted off, and they are prone to spread from gas pressure, and removal/installation.



Beefed up three prong flash suppressor, was used from 1963 through part of 1967 on late AR-15's (Model 02), the M16, XM16E1, and some early M16A1's:



Soon after M16A1 production and just prior to chrome being added to the M16A1 chamber the flash closed "bird cage" suppressor was introduced:



The M16A2 went into production with a new flash suppressor that omitted the bottom slot so as to decrease the dust signature created from firing.  Also used on the M16A4):



Early lock washer on left, as used on the AR-15, XM16E1, M16, and M16A1.  Middle is the A2 peel washers used to time the A2 flash suppressor to TDC on the M16A2 and early A4’s.  Right is the current crush washer used on the A4 starting in 2000:



Special thanks goes to Model_One , captrichardson, tgus, and Victor Mederos (US Anodizing) for thier assistance in gathering info on 601 barrels.

Colt had no rifle barrel manufacturing capability at the time that the Colt/ArmaLite Model 601 into production in December of 1959.  Model 601 barrels were made by Winchester, six groove, 1/14, and broach cut.  These barrels were originally turned down to app. .565" in front of the front sight base.  

This early example is stamped with two W's, one under the FSB, the other just behind the handguard cap near TDC.  The M is stamped on the exposed part of the barrel between the legs of the FSB on the right side.  This barrel also has a witness mark at TDC, and the gas port hole is counter bored:



Close up of the exposed M marking on the right side:



W stamping under the guards and behind the handguard cap:



Colt increased the diameter of the AR-15 barrel beyond ArmaLite's original specs during production of the Model 601.  Diameter was increased from app. .565" to app. .575" in front of the front sight base.  This barrel profile was carried over into 602/603/604 production.  These later 601 barrels have not been observed with the counter bored gas port.  Here are some examples of markings that CAN be found on these later production Model 601 barrels:

Barrel extensions were stamped stamped with a C at the 12 o'clock position:



Small upside down V stamp, can be found on either the left or right side of the barrel between the legs of the front sight base:



M&S stamping on right side between legs of the front sight base.  This is probably the most common 601 barrel marking:



C in Square Colt proof mark on barrel breach:



Colt Verified Proof V&P in triangle marking on left side of the barrel between the legs of the front sight base:



M1 stamped in front of the FSB (photo needed... I have 2 of these barrels so I can post mine. @ Model_one are you still with us?):



W near the muzzle (photo needed... @Model_one are you still with us?):



While the standard 1/14 .224 barrel twist was quite successful in commercial firearms it did not serve the AR-15 well. M193 ammunition utilizes a boat tail projectile rather then the more common flat base. Boat tail bullets have less bearing surface to engage the rifling of the bore then flat base bullets of the same weight. The result was that the 55 grain FMJBT bullets were on the edge of stability when fired from the AR-15.  Accuracy testing conducted by the US Army, US Air Force, and the NRA showed unacceptable accuracy with the 1/14 twist.  Because of these factors a twist change to 1/12 was approved on July 26th, 1963.

Here are some examples of markings found on a 1/12 twist Model 601 barrel (photo needed... @tgus are you still with us?):






Model 601 production ended in 1963 and was replaced by the Model 602. The Model 601 was chambered differently then later Colt rifles. These barrels were chambered per ArmaLite specs with significantly shorter leade/throat then was used from the Colt Model 602 through current. With the exception of examples with heavily worn throats 601 barrels gauge a 0 with my commercial T/E gauge. 602 and later barrels gauge a 1.25 when new with this same gauge.

Model 602 barrel were manufactured in house were proof tested and like some 601 barrels were stamped with Colt's proof stamp a V & P in triangle (Verified Proof) on the right side, the barrel extension was also marked with a C (C stamp was used through 1965):



A "12" marking was added just over and inch from the muzzle to differentiate it from the earlier barrels.  Marking was used from 1963 till the Fall of 1967:



In 1964 Colt’s began marking a M next to the VP marking meaning the barrel had been magnetic particle testing after proof firing to find potential flaws in the barrel:



By 1966 barrels were proof marked in the same spot as before, but the proof symbol was changed to a P, so they now simply read MP, with the M & P run together.  This MP marking was moved by 1969.



Starting in October 1967 and prior to serial number 800,000 Colt’s added chrome to the chamber.  Chrome chamber barrels are identified by a C about an inch back from the muzzle rather then the earlier 12:  



Rather then being marked on the right side some H&R barrels were marked with an unside down MP on the left side.  These barrels had chrome chamber, so they also had the C mark near the muzzle:



Chrome chamber barrels were also plated in the barrel extension:



By 1969 and before serial number 1,750,XXX Colt's chrome chamber barrels were marked C MP C, and the proof markings and C were moved to the same spot.  This marking was used as late as 1970 or 1971 and serial number 4,552,XXX.  The C means Colt’s, the M means Magnetic particle inspected, the P for Proof fired, and the C near the muzzle for Chrome chamber.  (late C MP C pic provided by yfs200):



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:



Effective in December 1971 at about serial number 4,700,000 along with the chamber the bores were chromed, early ones were marked C MP B.  The C means Colt’s, the M means Magnetic particle inspected, the P for Proof fired, and the B for chrome Bore.  The barrel extention on these not chromed:



Starting in 1974 and after serial number 4,900,000 chrome bores were marked C MP CHROME BORE.  This marking was used all the way until the end of M16A1 production:



M16A2/A4 barrels are marked C MP 5.56 NATO 1/7.  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 earlier rifles.



Sometime in the mid 1980's a star is stamped on the the barrel near the chamber area.  This is probably a precursor to the later O stamp indicating a chrome chamber and bore:



Some mid 1980's barrels are stamped 885 under the handguards, meaning unkown:  



Starting as early as 1989 a single or two digit code by the front sight base is used, this one marked 28.  Not sure of the meaning, maybe a lot code?



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



Starting in 95 a date code is stamped by the front sight base (earlist know is 02/95).  First two digits is the month, second two digit number is the year, this one 03/02 (gas tube is yellow from full auto 30 round mag dumps, so yes I do shoot em):



Beginning in the late 90’s a paint mark is added in front and under the barrel nut, not sure of it’s meaning:



ArmaLite front sight base was cast.  This part was used on the AR-15, and early M16, and XM16E1 rifles:



The cast front sight base was replaced by a forged part for obvious reasons. The first version of the forged front sight base was machined smooth to remove forging flash and used on M16 and XM16E1 rifles, and on the M16A1 for a time.  Production started as early as 1964, and was used as late as 1969 and serial number 1,750,XXX.  A bottom drain hole for the front sight post assy was added in 1967:



Transitional forged front sight base with C but no Bell. There isn’t much info out there on these, but it is assumed these would have been made somewhere between 1965 or 1966 and 1970.



Later forged front sight base used on later M16/A1 rifles.  These usually have a raised C and a Bell.  The C and a Bell was in use by 1970, and serial number 4,500,000:



Early M16A2 front sight base same as a late A1 FSB with a C and a bell but with a .750" barrel journal.  This FSB was used as late as serial number 6,210,000:



Mid to late M16A2 barrel has a raised Bfi marking inside a diamond, can be found on left or right side:


(photo by xcibes)

Colt M16A2 conversion kits/replacement barrels, M16A4 FSB's and late replacement M16A1 barrels have a jibberish forge code:



The M16A4 front sight base is similar to the late M16A2's, except that the platform the sight post screws into is higher, these are marked with an F on the left side:



Front swivels were originally bare steel, and secured with a roll pin:



Starting in 1964 the swivel is rubber coated, and was riveted on by about 1970 and serial number 4,500,000:



Early front sight post was round.  One 360 degree rotation equaled 5 MOA, one click equals 1 MOA:



Current square sight post used on M16A2 and M16A4.  One 360 degree rotation equaled 5 MOA, one click equals 1.25 MOA:



ArmaLite gas tubes were carbon steel.  These were used on the AR-15, and on the M16/XM16E1 for a short time before switching to stainless steel:



New bend was in use by 1969 and serial number 1,750,XXX:



Since Colt did not make their own handguards and used multiple vendors, and handguards are frequently replaced on USGI rifles this is a real tough subject to pin down. I don't have dates on all of these, but do see several distinct variations. This does not come close to covering all the details, but will give you an idea.

Type A and B.  Top is first production brown fiberglass, bottom is brown fiberglass painted green paint, or "B".  Notice that the heatshield is different:




Type B.  Far as I know all 8,500 of the Model 601's that AF General LeMay purchased were all painted green.  Same story with the 1,000 601's purchased for Project AGILE.  Note the highlighted area and red markings:



Close up of highlighted area:



Type C, now black impregnated.  Starting in 1963 with the Colt Model 602 the furniture is black.  These handguards are the same shape as the Type B, note that the highlighted area is the same as the earlier guard:



Both Type B and C handguards are frequently marked with red markings on the heat shields (Type C shown):



Type D is the same as Type C but now has a new shape in the highlighted area:



Close up of highlighted area:



Type E, same as D but now with "drain holes" added to the heat shields:



Type F handguard heat Shields are marked L and R for.  There is numerous variations of these types of handguards and I am far from figuring them out:



A2 handguards were used on the A2 and the A4.  They range from matte to gloss.  At this point I am thinking that the gloss ones are replacement parts rather then factory original.



This A2 handguard is marked DO NOT REMOVE, mold marks are present at every circle (highlighted).  Note placement of bend in shield:



This handguard is not marked DO NOT REMOVE, mold marks are present at every other circle (highlighted).  Note placement of bend in shield:



This A2 handguard is marked DO NOT REMOVE, mold marks are present at every circle (highlighted).  Note placement of bend in shield is at a different spot then the other two pictured above:



Starting in 1999 the heatshield tabs were glued to the handguards:

NOT PICTURED

ArmaLite handguard retaining ring used on the AR-15, M16, XM16E1, and the M16A1:



Handgaurd retaining ring used on the M16A2, and the M16A4:



ArmaLite port door. This part was used on the AR-15, and early M16 and XM16E1 rifles, and was dropped in 1964:



Later M16 and XM16E1 rifles used a new port door starting in 1964. This port door was also used on the M16A1:



The M16A2 came out with a new port door that is still in use today:



Bolt/carrier groups.  Top is the early AR-15 and M16 bolt group, no forward assist cuts.  Later transitional M16 bolt group is not pictured (mix of chrome and parked parts).  Second down is the early XM16E1 bolt group, has added forward assist cuts.  Next is the late XM16E1 and M16 and early M16A1 bolt group, now parked (transitional bolt groups are a mix of chrome and parked parts).  Third from bottom is the later C marked M16/A1 bolt group.  Second from bottom is the M16A2 bolt group.  Bottom is the M16A4 bolt group, it is parked a lighter color:





Top three pictured carrier keys are staked with two strikes, some were done round, and other square (pictured).  Bottom three carrier keys have a more secure stacking method that has been in use by 1967:



Bottom three carriers are marked with a C makers code, this went into effect in about 1967, and can be found on M16A1 carriers with serial numbers as low as 807,XXX.



Starting in the about 1995 a step was added to the carrier right behind the firing pin retaining pin.

Right view:



Left view:



ArmaLite firing pin on top, current on bottom.  Old part caused slam fires, and the new Colt’s design was put into production in 1963:



Early machined ArmaLite firing pin retainer:



Current firing pin retainer:



The forward assist was first used on the XM16E1 in 1964. This part was also used on the M16A1:



A new forward assist was used on the M16A2, and was used as late as serial number 6,280,000:



Newer A2 forward assist went into production in the late 1980's.  This part is still being made for use on the M16A4:



ArmaLite charging handle was cool looking, but was hard to grab onto, it was replaced at about the same time that the M16/XM16E1 went into production in 1964



ArmaLite bolt stop used on the AR-15, and early examples of the M16 and XM16E1:



Transitional bolt stop.  These were used sporadically and can be found on serial numbers as low as 40,XXX in 1964 and as high as 138,XXX in 1965:


(photo by tgus)

Current bolt stop in use since 1964 (need photo...):



ArmaLite edgewater spring guide. This part was used in the AR-15, M16, and the XM16E1 until Dec 1966 (need photo...):



The spring guide was replaced with a buffer at about the time that the XM16E1 was adopted Standard A. It is still in use. There are some variation in buffers, hope to have pics up later (need photo...):



Type A buttstocks were brown fiberglass and after the first 100 rifles or so they were painted green:



Type B was in use sometime before serial number 8,000, the shape of the buttstock was changed.  Note the angle at the bottom where it leaves the back of the lower receiver.  The rubber coated swivel on this example is a replacement part:



Type C appears to be the same thing as B but now black.  This buttstock was used first on the Model 602 in 1963:



Type D is also black, but has a slightly different shape and was first used on the 604/603 in 1964:



Type E has a trap door for a cleaning kit, was introduced in 1971:



The M16A2 buttstock is about 5/8" of an inch longer then the earlier models.  Because of the increased length it used a longer buttstock screw and a spacer.  The swivel is mounted closer to the buttplate. This buttstock is currently used on the M16A4:



Type A, B, and C buttstocks are smaller in diameter then the receiver ring at the back of the lower:



Not only was the Type D a different shape then earlier buttstocks, it is also thicker and fits flush with the receiver extension ring.  E and A2 buttstocks also fit flush:



Far right buttstock is a Type D and has a hole drilled in the front face (that white spot).  Most Type D buttstocks have this feature, while the other buttstocks lack it (also note the different lower contour on the D buttstock compared to the C next to it):



Type A through D have a glued on buttplate (early examples had a ArmaLite logo):



Type E had a trap door for buttstock (there is quite a bit of variation in these buttplates and trap doors that will be covered later):



A2 buttplate is checkered along with the trap door:



Earlist version of the rear swivel rotates 360 degrees.  The roll pin that retains the assy is also located in a different spot, so this swivel assy should not be interchangeable with later buttstocks.  It is unclear wether or not this part was dropped from production prior to the first US Air Force contract:



Type A, B, and C buttstocks lacked a rubber coating on the swivel:

Type A:



Type C:



Type D buttstock had a rubber coated swivel starting very early in production in 1964:



Type E had a fixed rear swivel that again lacked a rubber coating:



A2 rear swivel, similar to the Type E but placed farther back, and not interchangeable:



From left;

early buttstock screw with no drain hole
first version of buttstock screw with drain hole
later drain hole screw with compound on threads
longer A2 screw
spacer used with the A2 buttstock and longer screw

Good job sir!!

My head is spinning.

Andrew, Thank you SO MUCH for taking the time to do this

Impressive, young Skywalker.

Ah, don’t give me credit. I’m just making the photos observable again. I’ll do what I can to improve the info though.

Nicely done sir.

We really need a GM/H&R section added.

Thank you SO much for taking the time to do this.

You are awesome for taking the time and effort to do this! THANK YOU!!!

Again, ‘twernt nothin’... i did it more for my sanity than anything else, and to save the info in the pictures from vaporizing into the photobucket nebula

I don’t know much about GM and H&R guns but I do think the info is lacking there. Not that Ekie was lacking info, because this thread surely took him a long time to build. We can build off of it. Open to other suggestions as well. It would be nice to get the timeline for the mess that are the 601 barrel markings. I’ll probably add extra photos as examples of certain things.

A couple of other thoughts that may not necessarily belong here:

I have compiled a list of all 601s I have personally observed either in person or have seen pictures of, otherwise meaning that they are still alive and kicking... I think I may build a “601s in the wild” thread with photos of those rifles.

I also have a HUGE amount of official reports and other documents on my computer. Most of them can be accessed on the interwebs... I will probably also build another thread with links to them.

And now that I’m thinking about it, I should probably go grab the “603 upper guide and just slap that info in this thread, unless the hive feels it should be separate. There’s lots that can be done to make info more accessible in this thread.

@VA-gunnut @Aimless any chance of stickying this thread?

A much needed redo,

Thanks for taking the effort to save this.

Wpns Man

A member came across a bunch of de-milled M16A1 lower receivers. He was selling them on the EE. I got one of the "dogtags" he made out of it.

SN is 9,5xx,xxx. I don't see that range listed.

Thanks for taking the time and effort to do this.  I have a number of pictures of the VN era carbine mag wells if you need them!

Yeah I bought one of those too. Considering they went through Fort Carson, I'm assuming Export model?



Thanks, I'll keep that in mind. Again, open to any and all suggestions about editing this thread, I just wanted to save it.

And I thought I was being original, when I made my dogtag from an apex kit; when they first came out. Lol

OP thanks for getting this reposted.

Excellent resource as I start my retro A1 project.  Thanks LT!

Not really my work, I just saved the thread.

Hi everybody,

Excellent work, thank you very much, I have learn many interessant things about history of the AR

Best regards
Christophe

Christophe,

Welcome. There there are many other great threads located here.

@Macpw added the C and no Bell FSBs per your request.

Thank you, I made a better Picture

Fixed it ^

Great job!  I reference to this all the time.  Thanks for putting this together.

This needs to be pinned to the top of the page

+1

They hid it in “information links” lol

What can we do to get it not only pinned but listed at top as a resource?

Call your local mods lol

....

Large round FA from 1974 to end of M16A1 production:

Attached File