It seems like most of the uppers available with 14" and 16" barrels have the “m4 profile” with the m203 notch. It must be market driven but why is this seen as desirable? It’s not even close to an optimal contour unless you have a 203. Not many do. I’m surprised that the 203 notch isn’t a rare specialty thing. Is there something I’m missing?
Weight savings. Yeah, that’s it, weight savings. 
I think it’s something the market initially adopted to sell rifles to the civilian market that “look” like the same rifles that the Military uses. Otherwise, I dont see a practical use for the M4 profile barrel.
Its good to see some of the forward thinking companies (BCM, Daniel Defense, etc.) making rifles with more practical mid-length and lightweight profile barrels for the civilian & LE market.
I don’t have an actual answer but if I had to guess I’d say it’s simpler for manufacturing purposes.
One less machine to buy since you have to make the 203 notch anyway.
It’s not “desirable” except that it’s cheaper than producing a whole separate barrel profile.
for some reason i always had it in my head that it was a thinner “pencil” barrel. not just a notch.
just found this in a search
http://www.ar15barrels.com/profiles.shtml
Nice link, glockeyed, very informative. Thanks!
I really have no idea, but I do know that the interest in that profile is dying down.
The consumer is becoming more educated and are wanting either Govt profile or pencil barrel designs.
C4
Why is demand for Government Profile increasing? It seems to be completely backward.
Govt profile is about the same weight without that goofy step in it (which does not help accuracy in ANY way).
C4
My answer to the original question is because it came on my first 6920 I purchased.
I have had a Colt 6520 since around 1994 or 95. Great gun that has a pencil barrel. I love the thing. But as my eyes matured, and Red Dot optics improved, my desire for a flat top gun got the best of me.
While I still own that 6520, I have obtained a few 6920’s over years the since the end of the AWB. If they had the option of a flat topped 6520, with a pencil barrel vs. a M4 cut barrel, I would have probably went that route.
Truth be told, since all of the training I have done the last few years, both on my one time, and at work, has been with either my 6920’s, or the Department’s Bushmasters & M&P’s (all 16" M4 type barrels), I have gotten used to the feel and balance of this type of barrel.
I don’t necessarily like the M4 profile, but I have gotten used to it.
Train with the guns and equipment you have, not with what you wish you had. Seems to work for me so far…
It’s gottahaveit syndrome. If the .Mil suddenly changed to a slanted 8-port flash hider with chrome lining and a bell hanging off of it, manufacturers couldn’t make/sell them fast enough.
Gun makers market heavily towards the LE/Mil market even though its a small part of their sales simply because they know the public will want to have whatever the troops are using.
I have an M4 profile barrel, but it isn’t because of any particular fascination with it. It just happened to be what LMT uses, and it looks “normal” to me on a 14.5" barrel. I hate seeing 16" barrels with it though. They just look wrong.
Jay
For some folks maybe. There’s not a huge selection in 14.5" barrel profiles that differ from the standard M4.
I’m more concerned with the make of the barrel than the profile. I don’t find the M4 profile to be heavy at all. It balances better than my SBRs for whatever reason.
For me the gun I wanted had that type of barrel. Other than that I don’t care about the cutout.
I hate the look of the 16" M4 barrel, but kinda like the look of the 14.5" and under with the notch.
The 16" barrel balances fine, but just looks wrong.
It was my understanding that the original A1 barrel profile was sort of like the lightweight or “pencil” type profile. They were bending under field conditions so the Army beefed it up distal to the handguards. They shortened it for the M4 then the 203 came out and the notch happened. That’s how we got the frankenbarrels on our M4’s. Someone with more experience can probably correct me if I’m wrong.
Now some of the USGI m4’s are HBAR profile under the handguards and normal government after. There are two vertical flat notches near the breach to, again, accommodate the 203. I’d love to know how the barrel harmonics play out in that bad boy especially with all the crap we put on our rails. Also, you wouldn’t believe how front heavy they are. I picked up an old M16A2 and it felt downright handy.
Anyway I just think it’s funny that the M4 profile is so popular given that almost nobody has a 203 or is performing bayonette drills. There’s probably nothing wrong with it on a combat carbine, but I like that Noveske profile a little better.
The first three of the four years I spent in the Marine Corps were with M16A1’s. My first AR15 after getting out was a Colt SP1 (Think M16A1 w/o the full auto and forward assist.) Both had what would now be called pencil barrels.
We were told the reason for going to a larger diameter barrel on the M16A2 was because barrels were being bent behind the front sight base by individuals using their M16A1’s with bayonet attached to pry open packing crates. Of course we were told this only happened in the Army, as a Marine would never do something as stupid with their rifle…
I do not know if this is true, but yes, I could easily see this being an issue…
The high CDI factor. 
I wish it wasn’t so popular. The Noveske barrel profile, or simply no 203 notch, or a lightweight, all of those are better.
Posers/Wannabees/CDI Factor/Marketing/Weight Savings.
I have 2 6920s, a Sabre Defense middy w/o the notch and a LMT MRP rifle rail w/o the notch, so I’m indifferent. I prefer the mid-length 16" barrel without the 203 notch, with a rifle rail for comfort and greater stability, but shoot all equally well. Now a pencil barrel with KAC rifle length URX would be the shizzle! 