So I posted this in another thread, but I've been thinking, and others suggested that we might try to put something together as a reference guide - I know in the Retro Forum, the reference guides are prety ubiquitous, and I think it could arguably be said, without them and the apparent interest in small variations, companies like NoDak Spud and the readily available retro lowers wouldn't exist.

Many of you here are exiles (or dual-citizens, like me ) from the Retro Forum for your interest in A2s - maybe we can bring some legitimacy to research on the A2!

It's already well known that many M16A2s are in fact conversions of older M16 variants to A2 specs, and either stamped, engraved, or electro-pencilled over and re-marked. For the purpose of this, we won't go into those.

When the M16A2 was developed, the military asked for several modifications to the original lower receiver forging - in particular, they requested the "receiver extension boss," the area where the reciever extension tube (RET) threads in to the receiver be strengthened to prevent damage. Furthermore, they asked that the area around the pivot (front) pin be strengthened. These changes were integrated into all new-production M16A2s, and the receiver forgings were revised to have the extra reinforcements.

It would appear that for the most part, the "A1" style lower receiver forging was discontinued - Colt would continue to build commercial and export rifles on the old forgings (since they couldn't sell them to the military) until they ran out, but it doesn't look like they bought any more. "A1" style forgings would disappear until NDS began producing them again a couple years ago.

That being said, most people simply assume that an A2 lower is an A2 lower, and that's that. In fact, there are at least four variants of Colt forged lower receivers, possibly more. There's also a fifth variation that I've been able to identify on commercial lowers. Also, Colt was not the only company to produce "A2 style" lowers for the government. In addition to Colt in its various incarnations:

Balimoy - Lower receivers only, originally intended as A1 replacement lowers, but A2 style forgings and many re-marked as M16A2.
FNMI - M16A2, M16A3, M16A4
Sabre Defence - M16A3, M16A4
Bushmaster - received a contract for M16A3s, however as far as anyone can tell, their contract was cancelled before any completed weapons were delivered - probably do not exist.

Here are the variations that I've been able to find document clearly so far - but I will need help from everyone to complete this survey, and there are some things the membership as a whole can do for me that might help out greatly in pinning down exact time-frames and other details.

Colt A2 Lowers:

The most noticeable variation is the receiver extension reinforcement area, earlier A2 lower forgings had a more "organic" looking transition on both sides where the threading is reinforced.

Early:



On the left side, you can see that the reinforcement "blends" to the lower. Compare to later forgings:




You can see the horizontal line where the reinforcements have been added is much more defined in the later forgings.


On the right side, the older style reinforcement kind of "bugles" about 2/3 of the way back on the takedown pin spring channel, looking almost "organic":




Looking at the same are on a recent forging, the takedown pin spring channel has been made "beefier" and the reinforcement has a shallow linear demarcation:




The final variation is the "intermediate" receiver boss - which has the profile of the "late" receiver boss, but the takedown pin detent spring channel is only visible just aft of the receiver before the stock:




Another difference in the lower forgings is the profile of the pivot pin reinforcement area, the earliest A2 forgings had pivot pin reinforcements, but they still maintained an A1-"ish" profile with a sharp curve into the magwell (first photo), which was then changed to a more gradiual and radiused curve (second photo). Early "receiver extension boss" lowers could have both styles, and the modern lower still has the late radius.

Early Radius:




Late Radius:




The most difficult difference to spot is the shape of the mag fence area where the pivot pin spring channel meets the vertical "leg" of the mag fence, because it's usually covered by an open ejection port, and requires specific lighting to notice.

In the earliest A2 forgings, the mag fence meets the pivot pin channel, and there is a wide "flat" where they interface. Later forgings have the mag fence leg more tapered and coming to more of a "point" where it meets the pivot pin spring channel:

"Flat" Mag Fence:






"Pointed" Mag Fence:



Of these two mag fence variations, the "flat" mag fence shows up on both early and late radius lowers.

From what I've been able to see, the five variants I have identified are:

Type 1 - Early radius, flat mag fence, early receiver boss
Type 2 - Late radius, flat mag fence, early receiver boss
Type 3 - Late radius, pointed mag fence, early receiver boss
Type 4 - Late radius, pointed mag fence, intermediate receiver boss
Type 5 - Late radius, pointed mag fence, late receiver boss

In terms of production dates, though I don't have specific dates yet - a couple things I have noticed:

Most "Large Pin" Sporters that have the full fence A2 lowers tend to have Type 1 or 2 receivers. Many of the transitional "small pin" Preban Sporters have them as well. I've seen very early M4A1 Carbines in SOF inventories that have Type 1 and/or 2 lowers, so they are "M4 era."

Many "ban era" MTs have Type 3 lowers - the "modern" or "Type 4/5" lower appears during the ban era, for example, I don't think I've ever seen a 6920 with anything other than a Type 4/5 lower, though I've seen 6520s and 6721s with different variant lowers with early receiver boss areas.

Non-Colt U.S. Property M16s:

Balimoy:







Balimoy receivers appear to be Type 1 lowers - you can see from these three photographs, that they have the early pivot pin radius, and early receiver boss. Unfortunately, I personally have never handled a Balimoy, and I haven't been able to see any photographs showing the mag fence to see if it is a flat or pointed type.

FNMI:

FNMI M16s appear to have at least two variations in markings - however, they both seem to be "late," Type 4 lowers. Unfortunately, most of the photographs that are clearly identified as FNMI are of the left side of the receiver.

Earlier FN lowers are not rollmarked - but have had their markings engraved in a "dot matrix" style with an electro pencil:


image courtesy of schaz42

M16A2, FT Sill, OK - Image courtesy of schaz42

Later marks are rollmarked:





image courtesy of schaz42



Sabre Defence:

The final company to produce U.S. Property M16s under contract is Sabre Defence. For those of you that are not familiar with the drama of Sabre Defence, we'll simply say Sabre is no longer with us and available to produce M16s. Their contract was extremely small to begin with, for M16A3s for the Navy and M16A4s for the Marine Corps, and I'm not certain whether they ever actually filled their contract before they went out of business. Needless to say, seeing one or getting one issued would be pretty noteworthy and uncommon.



While this is the only good photo I was able to find of a U.S. Property marked Sabre lower, unlike the other two non-Colt manufacturers, Sabre also sold receivers commercially, that are well photographed - it appears that Sabre used Type 4 lowers, making it rather unlikely that they used any other variant on the U.S. Property marked lowers.

A final note about the above photograph - the lower is marked M16A3, yet the upper is an A4 upper. As far as I've been able to find, this is "wrong," as the M16A3 should have an A2 upper. There are a couple of possibilities:

1. The M16A3 spec has been changed to use an M16A4 upper receiver, and new production M16A3s are coming with A4 uppers. This is possible, and even sensible, but I haven't seen any documentation that indicates that such a change has been made.  Supposedly the most recent -23&P (UNIT AND INTERMEDIATE DIRECT SUPPORT MAINTENANCE MANUAL) for the M16/M4 FOW lists the M16A3 as having a flat top M16A4-type upper receiver.

2. This photo shows a tag for SHOT SHOW 2010, it is very possible that when putting an M16 on display, Sabre didn't want to appear "behind the power curve" and display a fixed carry handle rifle - so they swapped the upper reciever with an A4 for the show, but returned it to its "as spec'ed" configuration for delivery.

~Augee

Sorry to necro-post and resurrect this - I was able to find several Colt M4s with what I called "Type 4a" receivers that I've managed to identify and document that I will be posting.  

~Augee

I'm interested in this.  Thanks for taking the time to post it.

I don't know how to delete this!!

Great photos in both!

Will update shortly!

~Augee

This really is a great post.

A couple of side questions though:

The caption to the FNMI photo above statest that FNMI "is the only company that produces m16a3 rifles". Is/Was that true?

Also, you note that during the FNMI era, "burst" became "auto". Was that only a change of wording from burst to auto, or were the mechanics of the trigger control group also changed to true-auto rather than burst at that time?

I can't see the difference begween the "flat" mag fence and the "pointed".

Interesting.  Augee, any info on the "Balimoy" receivers?  Were they indeed military, or merely engraved like Pete's Legal Transfer RRAs?

I believe Bushmaster or Rock River produced base dummy rifles for one of the Army's marksmanship training machines (Weaponeer, FATS, or something like it) before they were replaced with Armalites, and they were engraved with "Property of US Government" as well.

I saw A2 rifles made by Balimoy in the hands of some sustainment brigade troops I was horsetrading with in Kandahar circa 2009.  The USMC FATS had bushmasters and as I have said many times over the years, back in the 90's I drew an M4 from an armory for a school I was attending (I had never heard of the M4 at the time) and it was an A2 uppered bushmaster M4 carbine.

Yes, no, kinda...

Colt "designed and developed" and delivered the original M16A2E3 ("third enhanced variation of the M16A2" - pre-production, but not quite experimental model) marked as such with U.S. Property markings.  However, I have not seen, and am uncertain whether or not any Colt "M16A3" marked rifles were ever built, if they were, it would seem they are quite rare compared to the E3 variants.  

If Colt did not in fact manufacture an "M16A3" marked rifles, it would be "true" at the time of publication of TBRII that FNMI was the only company to produce full rate production USGI M16A3s, and the only company with a currently active contract for them.

However, Bushmaster, then subsequently Sabre Defence were awarded M16A3 contracts in 2008-09 as well, though Bushmaster's contract was cancelled without any examples delivered.  Not certain on the Sabres, but if any were - they were extremely small in number.  

Not sure what you're asking in the second part of the question...

The original M16A1 was an S-1-F weapon, while part of the M16A2 "improvements" was the modification of the FCG to fire S-1-3.  The BURST FCG was redesigned, and IMHO, both more complicated, and less reliable and consistent - because it involves a non-resetting rotating cam on the hammer, not only does it offer three different trigger pulls - one for each "notch" of the cam, but it also means if you fire to bolt lock on burst, but your final burst was only two rounds - the next time you pull the trigger, expecting another three round burst, you get a one round burst, and have to pull the trigger again.  

As far as I know, the M16A2E3/M16A3 was simply an M16A2 with an M16A1 FCG installed in it and re-marked for S-1-F.  

While the M16A2 was type-classified in 1983, the M16A2E3 didn't come about until around 1992, and the two served side by side, but the full automatic mechanism is older than the three round burst mechanism, which was redesigned.



The difference is where the vertical "fence" around the magazine release button meets the pivot pin detent and spring "fence."  If you look to the top right of the magazine release button and look closely at the contouring at the "T" junction of the fence, you can see the difference, where the "flat" fence kind of "blobs" into the pivot pin fence, while the "pointed" fence is contoured as if to come to a ^ where it meets the fence.  



The Balimoy receivers were originally intended as M16A1 replacement receivers (if you look closely at the photos, you can see that they've been overstamped "A2" and "BURST") despite being A2-style forgings.  

Per D.E. Watters 5.56MM Timeline, they date from around 1988:



There have been some other companies that have gotten small contracts for training aids - like the Olympic non-functional M16A2 contract (with blue furniture!), and Armalite and Bushmaster weapons being used for simulators.  

There is still to this day no evidence of any U.S. military contract Bushmaster rifles or carbines.  There have been one or two that have popped up here and there of unknown provenance, such as one that showed up in a 2ID HHC arms room - with a 16" DPMS 1/9 barrel of all things.  They are not and have never been a USGI contract item.  

The only questionable contract that has ever been documented is a 65 carbine order in the early-1990s, with no evidence of where they went or what happened to them (i.e. they could have been FMS, a "gift" to a friendly dictator, agency purchase, ect.).  However, it has been stated by reliable sources that these carbines were delivered with Eagle Arms lower receivers, and would not even have been Bushmaster marked.  

~Augee

Sorry for newbie question, but can a AR15 stripped lower be used for an A2 build?

Updates to OP:

Have changed the "Type" lowers to include an "intermediate" lower, and renumbered the Type 4 as the Type 5, and listed the Type 4 as the intermediate:

From what I've been able to see, the five variants I have identified are:

Type 1 - Early radius, flat mag fence, early receiver boss
Type 2 - Late radius, flat mag fence, early receiver boss
Type 3 - Late radius, pointed mag fence, early receiver boss
Type 4 - Late radius, pointed mag fence, intermediate receiver boss
Type 5 - Late radius, pointed mag fence, late receiver boss

~Augee

Just to throw this out there...

I am a 91F, Small Arms Repair Technician for the Florida Army National Guard... I work full time and we have racks full of almost every configuration M16A2, M16A4, M4 and M4A1. Our inventory varies as our facility repairs every weapon in the state..

So what I'm saying is, if you guys need any detailed pictures of Army configuration M16s/M4s, please let me know. I can post them here or through PM.

Just let me know!

Here is a Colt A4, just for reference, use as needed

Augee,

Great information contained here, I think we all appreciate your contributions throughout AR15.com.

Thank you,

openbolt

Augee,

I saw Sabre Defence A4s in person last May at MCAS Yuma.  Marines assigned to MAG-13 had them.  I'll see what I can do to get a picture of one.

Semper Fi,

Sabre Defense M16A4, MCAS Yuma, AZ.

Thanks!

That's a great one!
~Augee

So, are there true sabre defense a2s or are they all a4s? Anyone have a nice closeup for us wanting to do an engrave of it on an 80?

Sabre A3 is an A2 upper with full auto instead of burst. I had an 80 engraved with the Sabre A3 markings, but  I spelled Defence with an S! Gonna use it as is.

That could be an awesome resource.  Please look for items that are not ordinary, such as different makes of lowers/ uppers/ barrels.  We have seen A2s with M16A1 lowers with Army Guard Units.  Of course the AF side has any combination.   Thanks for the offer MauserMatt

Second that! Thanks

 

What would be good to see is the feed ramps for the various combinations.  There's a lot of confusion out there with the 14.5" and 20" barrels, M4, M4A1, A2 and then A3/A4 and the feed ramps they're supposed to have.

A2 carry handle uppers with feed ramps and without.  A3 & A4 uppers the same.  Then the M4 and M4A1, which should obviously have the M4 feed ramps.

Hey guys.. Sorry I don't get on the A2 boards too much..

I still work full time as a small arms repair tech... So if I can help with pictures or questions regarding... Well just about any small arm in the army inventory... I will help with what I can... I can't take pics inside the vault of course, but I have my work area that would not jeopardize security requirements.

There's only 3 of us in the state.. So we do get a lot of hands on time with most of the Florida guard's weapons. Whether it be from individual weapon repairs or entire units going through their biennial gauging requirements, I've probably touched every Florida guard weapon in the state. So ask away!

And probably best to send me a PM or an email to get my attention.. Like I said, I don't get through here to the A2 board a whole lot...

I'll see what I can do for some pictures....

looking forward to the pics mauser matt, thanks for the opportunity

Got a little busy today and the other two guys are out for a few days. I'll get some pictures posted next week. Any requests besides feed ramps?

Any M4s w/ fixed carry handles - priority
Offbeat makers/restamped M16A1s/XM177s
Any M16A2s w/ collapsible stocks &/or railed forends

I know right now I think I have the last 5 M4s in the state that have plastic handguards (owned by the Florida guard anyway). And in fact, that's why they're in the vault, to put some rails on them. I don't know how these few M4s escaped the Modification Work Order process that was supposed to have that work done already... But they slip through the cracks. Part of that MWO is the replacement of the carry handle with the Matech back up iron sights... We had found a few of those carrying handles floating around a couple years back, but they've been "converted" now.

My inventory is always changing.. Just depends on when Joe decides to break his rifle as to when I get it. I know of one unit on post that has quite a few crossed out M16A1 lowers and even a few Hydramatics and H&R guns.. I think I've taken pictures of them before, so I'll dig through my pics to see if I saved them.

There was one deploying aviation unit a few years back that had apparently ordered enough collapsible stock "kits" to convert their entire inventory of M16A2s to them. We did that for them, but when they came back the weapons go through a reset program. That reset team more than likely converted them all back to regular stocks. No idea where all those parts went....

The army is changing to exclusively the M4A1 soon. The word on the street is my state will be completely M4A1s by 2018.... I'm pretty sure I know what's going to happen to all those old M16A2 parts...... But maybe maybe maybe Trump will reverse Bill Clinton's directive to destroy old army weapons....

Here is the oldest Colt M16A2 I have in my vault right now.

And here's the "youngest" I have in my inventory at the moment:

And finally, my oldest FN...















I hate the markings on these FNs... Who in the world thought that was a good idea???

hell yeah, thanks for the pics Matt. interesting the colt with FNMI barrel

Dupe

No problem!

When I see that, it just tells me at some point that the original barrel was shot out and replaced. It really just depends on the who the army is buying parts from at that time. I get replacement parts from all sorts of different manufacturers. Lately, replacement M16A2 barrels have been coming from FN. M4/M4A1 barrels usually come from Colt. In fact, I haven't seen any FN manufactured M4s in the state.

Are you going by ANAD rebuild dates?  Those two Colts look pretty close together in production, based both on features and serial numbers.

~Augee

Just based on serial numbers.

I'm sure they're not far apart at all as far as when they were manufactured. And their ANAD dates are the same.... So I'm not sure I understand your question.... I would think a 618xxxx was manufactured before a 649xxxx.... So those are the "oldest and youngest" Colt's that I have in my inventory at the moment......

Didn't look very closely at the ANAD date codes (was on my phone), just that they had them.  Was just wondering how you were determining youngest and oldest because the two rifles look close in production.  

It's not an attack on your methodology, it would be interesting to see a side by side of an older production and newer production A2 that could highlight some of the variations that this and the upper thread are talking about.  

~Augee

No worries! My inventory changes constantly, so as soon as I get a few older ones in, I'll post some more pics.

Superior images MM!
Thanks

Is there any way to recover the lost images in the first posting?

Google Photobucket Fix.  Download & install in your browser.

Tried that months ago. Didn't work.

Would seem the missing pics have been deleted.  You can see if they're available in the Internet Archive.

Thanks for taking the time to post it.

Unfortunately, I no longer work at the small arms repair facility I was at... I know the guys that still work there, so I could potentially get pictures. But I no longer have any idea what the inventory is anymore.

Send us cool pics of "antiques" you buy @ the bazaar before you send them home.  And stay safe!  You're likely allergic to rockets.

Can somebody tell the story about the a3 reinforcement? I have 2 lowers like this. Was the “a3” reinforcement introduced 2001?
I bought them in two deactivated 727 with 203. The story was that these were ex US Army with Papers.
The Front Pin reinforcement looks like the "Early Radius"

Saw an Armalite lower on an M16A2 EST trainer last night.

Got to fuck around with a Colt M16A2 lower with A1 front pivot pin profile. Turned into a dedicated simunition gun by my agency.