Is there a current source for new A1 lowers ?

The M16A1 lower is impossible to distinguish from the M16A2 lower without holding the two side by side (or you've seen hundreds of them).

Both the A1 and A2 lowers have the fence around the magazine release.

Other than minor machining, the XM16E1 and SP1 lowers are identical.  The distinguishing feature being no magazine release fence.

A "Vietnam era" rifle will be slabsided like the SP1, but contain the upper with forward assist.  Only USAF used the XM16 which lacked FA other than a few hundred early rifles.

By 1968 the 3-prong flash supressor had been officially replaced, but like the slab sided lower was common in the field.

-- Chuck

Think something got left out of the chronology, or I'm misreading the above.  The first M16s and M16A1s had the ridge for the push pin spring and detent, but did not have the mag release fence. The fence, as I recall, came in about the time the bird cage suppressor was adopted, tho not concurrently. Got pics somewhere stashed that show GIs in Viet Nam carrying M16A1s w/o the fence.

Whoops; just went and pulled my TM 9-1005-249-14, dated 1 August, 1966, on the Rifle 5.56 mm, M16; Rifle 5.56mm XM16E1 and Launcher, Grenade 40mm, XM148.  Sure enough, all pics of rifles, both with and without FA, show a lower with the long hump and no mag release fence.

The February 1972 version of the same manual shows the mag release fence in all pics.

Yeah, but if you look at the buffer area you can tell mas rapido.
GG

The other noticible difference are the extra reinforcements the A2 has around both reciever pins.

Actually, the magazine fence was in common use on the M16A1 by 1968.

[url]http://www.ar15.com/forums/topic.html?b=6&f=2&t=169380&w=searchPop[/url]

Here's a pic (I hope) of my A1 lower, a preban Sendra, that I built up into a lightweight.
[img]http://pic6.picturetrail.com/VOL176/1171244/2214857/26820068.jpg[/img]

The top ridge doesn't just hold the spring and detent, if it wasn't there, the ejection port door would slap down flat against the lower and you wouldn't be able to get it back up again.  Not trying to be a stickler, but it is something a lot of people over look.

Ok and a question for all of you guys/gals with Vietnam era knowledge of the AR.  How were the original 3 prong and A1 birdcage(slots all around) flash suppressors at doing their job?  I would think that an A1 would have less flash and be more accurate than an A2 just because it is symetrical and maybe the slots aren't loaded up as bad.

I didn't know, just hoping you guys do.

Are you saying that those of us with flat side SP1s can't lift our port doors back when they're opened? Those lowers don't have the ridge on them.[:D] And nearly all of them have a shiny impression of the door ridge on the lower[;D].

Actually, having that "tunnel" on the lower CAUSED problems with the A1 port doors.  Because the center piece was flat, if you tried to close the action w/the port door open, and didn't hold it out of the way, the top front edge of the door would hit the ridge on the lower, and bend the door and that point.

That's precisely the reason that the M16A2 has a port door with a tapered center piece. It holds the door just far anough off the width of the ridge for the door not to hit that ridge when you're closing the top and bottom recievers; and on the SP1s, it keeps the door edge from making even more noticable outlines on our lowers.

It's also the reason that both my M16A1 clone, and my SP1, have late model A2 port doors on them[:D]  BTW, my A1 clone, which has a milsurp Colt M16A1 upper, came with a bent port door.

Though I've never personally done a night fire test on them, the general word is that the early 3 prong suppressor was the most effective at doing it's job. It was supposedly replaced b/c the open prongs were getting snagged on the brush and vines of the Viet Nam jungle, and I've also seen it printed here that it attracted more water into the muzzle (can't vouch for that myself).