So I'm working on building an M16A1E1 clone, and am attempting to guide a couple build purchases. I've done extensive studying, but there are some questions that I would appreciate help on. All my previous builds I've dedicated exceptional time to, and would really like this to be no exception.

What I've learned thus far:
The M16A1E1 has a MAJORITY of A1 parts, that were over time phased to the A2 parts before the production began. A2 features included the use of the tapered slip ring, A2 flash hider, the peel washer (with/without the crush washer), A2 hammer/trigger assembly (with both auto/burst disconnectors), A2 handguards, 0.750 diameter FSB/HB, A2 length stock (A1 buttplate).

1.) I am aware that the barrel was .750 forward of the handguards, however I am reading conflicting reports on the profile UNDER the handguards. A couple of sources indicate that it was a HBAR only near the FSB forward, and otherwise was a pencil profile. Other sources don't specify, and one site alluded to the possibility that the barrel was a true HBAR and the hybridization only came after the introduction of the M16A2 after complaints arose based on weight. I saw one other weapon from around that timeframe that features the same barrel profile though, so I'm inclined to believe the "partial HBAR" theory, but would love to have more conclusive assessments.

2.) Does anyone have pictures of the elevation wheel and a close up of the rear sight apertures? I know that the aperture was marked with an 8, and was at a different height, so the sight aperture was only flipped when adjusting to 800m. However, I do not know if it is possible to replicate this, so I would be grateful for any help with regards to this part so that I could potentially remanufacture it. Ideally I would really like to make it authentic.

3.) My assumption would be that the rear sight wheel would be threaded differently so that the elevation would be accurate in the back window, not on the left side. Does anyone know how hard it would be to bore it to bring that rear sight to the rear authentically?

Thanks in advance, and I'll try to post updates/progress once things really start going underway.
v/r,
Jon

Here is a little info.

http://pullig.dyndns.org/retroblackrifle/ModGde/ProtoGde/645.html


Also, I found this info.

Model: 645
Military Designation: M16A1E1/PIP
20" Barrel w/ Bayonet lug: A2 profile (1:7 twist)
Handguard Type: Full-length ribbed
Buttstock Type: Fixed A2
Pistol Grip Type: A1
Lower Receiver: A1 or A2
Upper Receiver: A1 or A2
Rear Sight Type: A1 or A2
Front Sight Type: A2
Muzzle Device:M16A1 or M16A2-style birdcage flash suppressor
Forward Assist: Round or Teardrop (?)
Trigger Type: Safe-Semi-Auto or Safe-Semi-Burst

I'm familiar with the page, as well as the images in Retro Black Rifle, and John Thomas' threads in the archives (as well as ones done by Boywonder777).  I'm still looking to get clarification regarding barrel profile and the above mentioned pieces.  From my thoughts, I think it would be easy to change the location that the thread meets the elevation wheel so that the rear sight assembly elevation would be authentic while being viewed from the back window, rather than the L side like the current M16A2 receivers....and then from there it would be a simple matter of getting an 800m rear sight assembly and finding a way to mark it appropriately (although I may need to forego the correct construction, since there were only 50 of them made, many of which are undoubtedly in museums or private collections that wouldn't just LOAN out a priceless piece of history).  

The rest of the pieces I think are probably going to be fairly easy, and will simply be standard M16A1 or M16A2 pieces.
v/r,
Jon

From what I have read, it appears that they used an A2 Gov't profile barrel. Of course, they could have used a heavy profile, but I have not seen anything to indicate that.

Some old threads, with good pics and info.


https://www.ar15.com/archive/topic.html?b=3&f=123&t=629893

https://www.ar15.com/archive/topic.html?b=3&f=127&t=529554

http://www.ar15.com/forums/t_3_123/494844_.html

https://www.smallarmsreview.com/archive/detail.arc.entry.cfm?arcid=2292

https://www.ar15.com/archive/topic.html?b=3&f=123&t=661000

The upper receivers were fabricated from A1 receivers, an elevation knob viewing hole was drilled in the rear of the upper, Brunton's case deflectors were fabricated and epoxied in place. These also had a unique windage knob on earlier versions.

Lt Col Lutz  (coldblue) could probably help with questions


If the elevation drum is not hardened, a new set screw hole could be drilled and tapped 90 degrees from the existing hole to allow elevation markings to be viewed from the rear.

Very close to the current 20" A2 Gov't profile barrels.

Some time ago, I snagged this upper, which looks to be a transition from M16A1E1 to M16A1E2 as it has what became the A2 rear sight.



Hard to make out the Colt proof marks



Standard A2 sight

From searching through the photos, I think you actually have an early A2 upper from CM, although I'm still interested in learning more.  So far I've seen 3 different A2 uppers that have the "C VP" upper receiver markings, all of which carry the forge code "CM".  (This receiver has one, yours, and then the one on the A2 builders guide or whatever that is stickied on the front.....I saw another one on gunbroker once, but I don't have photos saved.)  Aside from the Rock Island Arsenal photo of the M16A1E1, I've never seen another mention of the M16A1E2 to identify features, and have been unable to find a second reference in any book to confirm identifying characteristics of the XM16A1E2....but if this is the case, this would be an A1E2 that has a hole in the back.  There's no doubt that the A1 style markings were early, but it seems to be a semi-common variant of CM receivers (from my own research).  
v/r,
Jon

I'm guessing that upper is from the first 100 test A2s, and there were not enough flat side big button assists to be had, so it got the teardrop.

OH NO!  Now I am really confused.
I thought I had the basic down pretty good.
The good thing is I have  some of those early upper receivers in storage along with some barrels.
Actually I have everything I need in storage.................
I see another build or two coming on this year, I have to finish several I started already.
THANKS EVERYONE...........

Ron

It looks like a basic early M16A2 upper that someone added a tear drop assist to. That F/A shows hardly any wear compared to the rest of the upper. It also doesn't look like a USGI tear drop assist. Looks more like a modern DPMS one.
All of the USGI tear drops I have (and have seen) don't have squared shoulders on the outside edge. That's pretty much a commercial part thing.

hahah....yeah..  I just finished my 601 and H&R M16A1 build, am almost done with the 602 (needing upper receiver and barrel only) and early XM16E1 (upper receiver only).  So I'm now venturing out into the wilderness.  LOL.  Some of these projects found me and I just thought they were kinda cool.....so....here we go.  LOL.   I'll try to keep my information and updates locked into this thread so that hopefully it can help others that get the wild hair lodged someplace...lol.  The unfortunate thing is that I may still need to make some concessions, as I don't know for sure that I'll be able to adequately replicate the ACTUAL A1E1 aperture.  Everything else is already figured out, but without exacting heights and diameter, then it's going to be a challenge to get a hole of the part.  Even with that, finding someone willing to manufacture a "one off" part is going to be VERY challenging (and probably cost prohibitive for many people).  As such, I may end up having to say "close enough" to the rear sight wheel being rotated and modified.  The windage knob I'm sure I can get remanufactured to be built up a bit, and I have some ideas on how to simulate an epoxied/welded Brunton bump.  
v/r,
Jon

The "duck grip" at one of those links is hilarious to me.

I never understood all the complaints about the A2 grip, I actually find it more comfortable than the A1 grip.  Then again I have gigantic Teutonic hands and I can manipulate the G3/HK91 selector lever without much trouble.

do you recall the barrel markings?  this is seems like an oddball with the standard C MP CHROME BORE markings like the 1/12 with the 7 stamped under it





your thoughts on this upper?  you think the hole was factory?

The guide indicates markings as "5.56 NATO" or "1/7" or both.  Chrome bore may or may not appear due to all barrels being chrome bored.  This is from the manual that was given to me by LTC Lutz.  
v/r,
Jon

So this variant was .650 under the hand guards?

I believe you are correct.  It was the same diameter as the pencil barrels, which I believe is 0.650 under the handguards, then the .625 FSB....
v/r,
Jon