So I got to talking ARs with a cousin of mine earlier. I was telling him about how I just picked up a KAC M5 RAS and the builds I'm planning on doing next. That was the fun part.

It somehow turned into a debate about the diffence between M4 and A4 uppers. I had a thread here awhile back where I asked you all the difference, and the overwhelming consensus to those who stayed on topic to the uppers was the only difference is feed ramps, which I was certain about. My cousin says there is a diffence in rail hight.

1, doing my due diligence, is there a difference in rail hight?
2, being certain it is only feed ramps, how could I proove that?

There is no difference in rail height between M4 and A4. The older A2's didn't have F-marked FSB's.

The .mil guys here will chime in and confirm not having M4 feedramps, but most commercial A4 uppers have M4 feedramps.

The ONLY difference is the feed ramps on the M4 upper (to be paired with M4 cut barrel extension) And no feed ramps at all on the A4 upper receiver (to be paired with rifle ramped barrel extension) There is no other difference.

I like pineapple.

As I suspected or knew and such.  I don't know where my cousin got his info, but goes to show there is a lot of bad info out there.




Like in a glaze on a ham?

Both of my colt AR15 A4's has feed ramps.

Colt did that to make manufacturing easier. Only one type of upper and barrel extension to make and keep in inventory.

The actual, real, US military issued M16-A4 does not have the ramps. That might change if Colt and/or FN convince the military that there is no negative to them on the rifle.

If rail heights were different then the issued back up sights, by Matech (and the possibly issued to some special units, Knight's) wouldn't work on both the rifle and carbine.

to be perfectly honest you can zero a normal FSB on a flattop upper but the FSP will stand very high

My understanding, is in the early days of flattop uppers there were some manufacturers who made uppers with the rail at a slightly lower height so that F height front sight bases would not be needed. I can't verify if that is true, but it was commonly discussed in the 90's.

I don't think that applies to anything of remotely current manufacture.

Even if this is true, it's irrelevant. Neither the M16A4, nor the M4... or hell any of the issued AR15s have different height rails.

^This^

From the Technical Manual, TM 9-1005-319-23&P Repair Parts List:


Three different part numbers [bold] and three different NSNs.  This would indicate there is a difference between an M4 and an M16A4 other than just the flat top.

Further:


The barrel assembly, which includes the front sight base, is the same for the M16A2, M16A3 and M16A4.  This would indicate that the feed ramps for the M16A4 are different from the M4 and the same as the M16A2.

Interesting that the TM lumps the A3 and A4 together, while the FM (correctly) lumps the A2 and A3 together....

The M16A3 received a quiet PIP around the time that the SDI contract was awarded, and the few A3s they manufactured had A4 uppers - and the A4 upper is now an approved repair/replacement part for the M16A3.  

I kind of wish that as they had done with the PIP, the same thing they had done with the A3 in the first place and re-named the M16A3 with an A4 receiver the "M16A5," which would be consistent with the original M4A1 nomenclature as well - and this could stick in the craw of all the people sticking Vltor "A5" receiver extension/buffer kits on their rifles and referring to them as "M16A5s;" rather than giving ammunition to folks who want to retroactively claim that "A3 receiver" is now "correct" nomenclature for a flattop receiver without feedramps, even though they were doing this for over a decade before the PIP happened... but they didn't.  

But nevermind that, I'm a well known nomenclature nerd, and I'm letting my spiteful side show.  

~Augee

Ahhhh....

Thing do get confusing when the Army doesn't follow their own rules on nomenclature.

(They probably didn't want to call it an M16A5, because Congress would have though they were buying a new weapon and killed funding...)

Holy jeeze... I didn't realize how many typos I left in that until you quoted it for posterity.  

~Augee