Checking in with the dissenting opinion:
I very much prefer the RO921HB profile ("SOCOM" barrel) over the RO920 government profile barrel.
The RO921HB, while called an "HB" is really more of a medium contour barrel as we would recognize it than a full HBAR.
Though I have not directly measured them out - IIRC, the difference in weight is four ounces. To me, given where it is placed on the weapon, I consider that relatively insignificant when taking into account the way the weapon balances.
The 921HB profile has less theoretical deflection when mounting a suppressor on the end of the long lever when talking about a 14.5" or 16" barrel, though some might argue that the deflection is imperceptible, and therefore irrelevant - it doesn't change the fact that all other things being equal - the suppressor causes more uneven stress on a government profile barrel at the weakest part of the barrel (under handguard behind the FSB cap where the narrow profile "flares" to the .750 FSB journal).
I also feel that a suppressed 14.5" with a 921HB balances better for me than a government profile barrel (I run both currently).
Also, when taking into account rates of heating and cooling and the effects on the barrel, I tend to prefer a gently tapered profile than the extreme changes of the government profile barrel, especially on aggressively used guns. If half the barrel is "lightweight," while the other half is heavier like on a 14.5" barrel - you've basically got the barrel heating and cooling at two totally different rates, which cannot be good for the barrel or for the steel. Granted, I have and use many government profile barrels - I consider them a good comprimise between weight and balance, especially on non-accessorized rifles, but my heaviest use rifles tend to use tapered profile RO921HB barrels.
I will say, I've carried heavy weapons before - and an M4A1 is not one of them. For the peace of mind it gives me at high round counts and with warm barrels, the four ounces is worth it to me if I'm building a gun that's meant to be a general purpose, heavy use weapon with as aggressive of a firing schedule as I can afford to feed it for. M203 cuts - well, for starters, unless something's changed recently, PSA's "SOCOM" profile barrels and Colt's 16" LE6920SOCOM profile are beyond pointless - without the milled flats, you can't mount an M203 even if you had one and wanted to. The forward "notch" is a completely cosmetic and vestigial feature.
On the other hand - I like at least the theoretical ability to mount an M203 - and if I can convince the better half, I'm hoping to budget one in to our household's FY '13 expenditures, but this yet to be seen.
Some like 'em, some don't, but as far as I'm concerned - it's a non-issue, while there may be some uneven cooling going on at the notch, it's nothing compared to behind the FSB on a government profile barrel, and it's much shorter than the lightweight portion of the government barrel. Under destructive testing - the government profile barrel catastrophically failed - the RO921HB profile can withstand sustained automatic fire sufficient to melt and cause catastrophic failure of the gas tube.
~Augee