Advantages of 20" AR Barrel???

[Skans]

So, I have done a little more research into my 20" NATO 1/7 government profile barrel, wondering what it was really designed for. This is what I've found, and it seems to make quite a bit of sense - I figured I'd share (but some may already know this):

Coldblue wrote:

Since The M16A2 Product Improvement Program (1980-1983) was my program, this is the down & dirty on the barrel thickness issue.
We (Marines) were replacing a lot of "bent" barrels that were determined to be "bent" because the Armorer's Bore Drop Gauge would not freely pass through some barrels during Ordnance Inspections (LTI's). So the Logisitcs people had "Barrels Bending" on their list of "M16A1" things to "Improve" right after listing "Handguards Breaking."
We "experts" thought this bending was from rough handling like during bayonet drills, etc., as an absence of any mid-barrel handguard damage in these rifles made one assume the fulcrum of such bending was the bayonet lug. So we made that part of the barel thicker because we did not want the excess weight of a full length heavy barrel. In testing using the bayonet lug as a fulcrum, and applying calibrated mechanical pressure to the muzzle, the new barrel was about 9 times more resistant to bend and take a set than an M16A1 profile. So we went with this "improvement."
However, soon after I started using a bore scope with a video recorder and monitor to inspect "bent" barrels. What I found was a mound of bullet jacket material at their gas ports. This build up was caused by a burr left from drilling/reaming the gas port. This was where the Armorer's Drop Gauge was geting stuck. When we removed this "mound", the barrels would all pass the Drop Gauge. We let Colt know what we had deduced, and that is one reason they kept models of "A2's" in their line-up with A1 profile barrels. However, the A2 profile was already down the road for the US Military. So about the only advantage of the A2 profile was to give the rifle a little more muzzle hang. This was noted by most all the Operational Test paticipants, especially when they fired the standing/off-hand leg of our rifle qualification course.
So my advice to mlitary armorers is to never replace a bent barrel until you visually check the gas port, or at least scrub the hell out of the gas port area with a new bore brush and an electric drill. And thank God for chrome bores!

[slappy]

What? You mean the military made a mistake? Interesting. I never would have quessed it possible. Another reason not to put so much faith in "mil-spec" huh?

[hornetguy]

One thing that hasn't been mentioned... AR's are somewhat loud, if you hadn't noticed.
The 20" barrel moves that muzzle blast 4" further away from your ears, which makes a difference. At least it does for me. The 20" guns are just more pleasant to shoot. My last one was a 20", but my new one is a 16"-er...it's just the way it came. I had nothing to say about it...

[Skans]

One more think I thought I'd add. I took out my micrometer to check the OD barrel thickness of the 20" government profile barrel as well as my SP1 Carbine "Pencil" Barrel. Here's what I discovered:

The OD of the government profile barrel actually tapers to almost (but not quite) the OD of the pencil barrel. I'm trying to recall the numbers, I think it was something like .675 down to .6; and I believe the pencil barrel OD is right around .5. The dimensions of the Government Profile barrel are strange to say the least. Lots of work seems to have gone into making something that is still over-engineered for what it was intended; yet still not thick enough for sustained full-auto fire.

[Justice06RR]

Question 1: I see most people using carbine length barrels these days for AR builds - hardly ever see any 20" barrels. Why is this? Is there any real advantage gained by using a 20" barrel. I figured I could gain a little more range with the longer barrel.

Most builds are catered for personal use, range, and maybe 2-gun/3-gun. The lesser weight and shorter barrel makes for a more portable and easier to wield AR15 which is why most people building them use a 16-inch barrel. They are also cheaper for obvious reasons.

Of course the 20-inch barrel will give you higher bullet velocity, and better cycling with a rifle gas system.

I was actually considering the Magpul UBR or PRS - so far, that's all I can come up with. If I understand correctly, the Magpul URB can't be to adjust along the buffer tube, just with the fine adjustments? Are these Magpul stocks really worth the price, or is there something truly as good for less money?

IMO the Magpul stocks are truly excellent products, (same goes for their other accesories). I would vote for the UBR stock to balance your rifle. My roomate has it on one of his AR's and it does feel heavy for stock on a 16inch M4, so it should balance the 20-inch rifle just fine. The solid cheek-wield is also a big plus, if you don't require fine adjustments like the PRS.