I was able to take these photos recently at the Rock Island Arsenal museum.
This is listed as an XM16E1 lower that was used as a testbed for features that would eventually lead to the M16A2. Why and how this XM16E1 lower is fenced is something of a mystery to me, but that’s what both the display and front desk said.
The two most notable features are the “Brunton bump” which is a massive brass deflector built into the upper.
The other is the proto-A2 rear sight. In this version there is a hole in the carry handle allowing the shooter to see the drum setting.
The windage adjustment knob is squared rather than cut at an angle on the end like the final A2 sight.
Woah that thing looks wild! Cool find! Interesting rattle can job on this guy, I’d love to hear the whole story about this rifle in detail (more than we can infer from just the info present here I mean of course), I bet it’s all absolutely fascinating. Would also love to see the inside of the lower, what’s up with that trigger/hammer pin situation?! And an A2 grip instead of the far superior A1 is interesting too, never liked that change, A1s were more fragile but better angle and size (all the varied A1s, thick or thin, better than A2 imo.)
This actually has an A1 grip, though it also has what appears to be an A2 stock.
Up front it has a heavy barrel that appears A2 but is fitted with an A1 flash hider.
The paint camo is a little strange for a design test rifle, but it takes almost no time to spraypaint so maybe the testers were bored.
Oh for sure it does, it looked like a weird A2 angle without the finger groove at first to me, no clue why. The flash hider is weird too, the A1s were three prongs, but the A2s had the bottom of the birdcage closed off like we’re used to, but this appears to be a fully open birdcage or improperly timed and we’re looking at the “top” of the FH, hard to tell from the pic. Nothing on this gun makes sense lmao, it’s cool.
The three prong flash hider was on the M16 and XM16E1.
The M16A1 had an enclosed birdcage that had slots all the way around.
The M16A2 had an enclosed birdcage without slots on the bottom.
Trust me I checked all the visible bits from every angle I could find. This is an A1 birdcage for sure.
M16 vs M16A1:
Here’s the clearest photo I could find on the fly showing off an M16A1’s flash hider that’s unambiguously a Vietnam period pic:
Huh neat, I’ve definitely seen A1s with three prongs in pics before, I guess sometimes parts probably just got swapped around as time went on (well they for sure did later, but I guess maybe earlier than I thought). Makes me feel better about the inaccurate frankenstein clone build I’m working on haha, technically I need an a1 upper but it’s getting an a2 becsuse I like them more and have a spare.
Cool Nam pic too, interesting he has his sling tied to the FSB instead of the sling mount, looks like a strip of ripped cloth or something.
As far as I’m concerned a repro that’s using backwards compatible parts is perfectly accurate. Sometimes repro builders get a little too hung up on what something is by the book rather than what it became in the field.
For the sling, yes mounting the front on the FSB is something you can see a lot in Vietnam. M16s were designed with all the sling points facing down, which reflects the existing doctrine of the time and the earlier doctrines that considered slings something used for marching and transport, but that rifles should be entirely unslung in combat. The M16s and Commando carbines (with the later carbine having their buttstock slingpoint facing up but the forward one down) were light enough that people started carrying them slung in combat, and figuring out that mounting slings on FSBs worked better.
At some point, which I unfortunately can’t pinpoint, the doctrine flipped to follow what people in the field had figured out and the modern U.S. military teaches that rifles absolutely should be slung in combat. You can see in early Iraq soldiers and marines still attaching slings to FSBs, as well as a ton of using up or side facing Velcro mounting points to achieve a similar outcome.
Edit: Here’s 80s and 90s Delta doing the same thing, giving a clearer view of the refined version of the technique.
It also looks tough to mount a sling to the swivel when you delete it and throw a 40mm tube there haha. Also did second from the bottom tape an optic to his carry handle? Surprised if that holds zero lol. Awesome pics!
Sling swivels and slings can fit on a grenade launcher equipped rifle, either in standard position or reoriented to the side by an armorer but I’m sure FSB mounting looks more attractive to most grenadiers.
With carbines the swivels pretty much have to be shifted to the side, but again just removing them is a lot more attractive I think.
The Aimpoint is on a Weaver rail interfaced with the carry handle. The best I can tell, that tape is just there as extra assurance, similar to seeing zipties and 550 on other optics and PEQs as a last line of dummy defense.
Here’s a repro builder’s clear photos:
Man I wish cameras back then had more pixels (or maybe the shot is just out of focus) I can’t see that side attachment point at all, curious where they drilled the rivet hole for the sling swivel lol. Also never seen one of those grenadier sights before, that’s pretty cool too.