Getting a flat top upper for a 20" 5.56 HBAR barrel and came across two listings for what I had though were nearly the same flattop uppers.

Interested in differences and any recommendation for a nice flattop upper.

A3 Carbine / M4 Upper Receiver Assy

Upper Receiver Assy M16A4

'Real' M4 barrels have enlarged feed ramps to work better soft point and hollowpoint ammo, and these ramps extend onto the upper receiver so 'real' M4 uppers have the feed ramp cuts.  But the term M4 gets used a lot and doesn't always mean the same thing to different people.  Some uppers advertised as M4 have the feed ramp cuts and some don't.  Some uppers not advertised as M4 still have the cuts.  Same thing goes for barrels, Colt M4 barrels have the feed ramps but with any other barrel or manufacturer it is hard to say.  

So the short answer is "don't worry about it, just get an upper from a reputable dealer and get on with it."

Not my nature to "not worry about it" always have to worry any project to death before doing it (that is half the fun [;)]

Thanks for the information and wonder if an actual USGI M16A4 has the "feed ramp" cuts of my Colt M4 upper?

Okay, let me see if I can answer this. REAL M4 uppers made by COLT have a “4” or “M4” stamped just above the gas tube hole (or star) on the UPPER. They also have the M4 extended feed ramps. REAL M4 barrels as made by Colt have matching extended feed ramps that match up to the M4 upper feed ramp cuts.

Here is a link to a pic of both the M4 and standard feed ramp cuts. Pic thanks to Troy.
[url]http://community.webshots.com/photo/29311363/62164402VZHXhm[/url]

The military has not requested the extended feed ramps for the M16A2/A4 so these uppers do not have the 4 or M4 stamp nor do they have the extended feed ramps. Most companies do not put the M4 extended feed ramps on their uppers. CMMG has had some made up by DPMS but this is not the norm.

So how does this affects you? You can put a barrel with the M4 feed ramps on an UPPER that does NOT have the M4 feed ramps. But if you put a barrel WITHOUT the M4 feed ramps on an UPPER that DOES have them you are setting yourself up to have feeding problems.

Many companies, like Bushmaster, make M4 profile barrels but do not put the M4 extended feed ramps on them BUT market them as M4 barrels. It isn’t a big deal unless you try to put the barrel on a COLT M4 stamped upper.

I have read here that some of the guys are sending their 20 inch M16A2/A4 uppers off and having the extended feed ramps installed by someone like KKF.

Edited to add: SAW LE Sales only carries Colt parts so this is an issue with the items you are considering.

I hope this clears this up.

Thanks for the back ground information.

Now that I have some idea, can check closer, however, looks like the A4 upper would be the best match for the Colt HBAR barrel.

Lucky,I am looking at the photos of the M4 feed ramps posted.I see the standard ramps end in what looks like a flat tooth.The extended ramp looks like it actually comes to a sharper point?Is this correct.The images are a bit dark on my moniter.Robert