Just your opinions...I am building an AR this summer and it will be my only rifle for a while. What are the advantages/disadvantages of a 16" barrel versus a 20" regarding range and accuracy?
Are the weight and length of a 20" AR really that different from a 16"? I was considering a 16" but recently liked the looks of a slightly longer rifle.
Also, would a 20" be too long for an 'urban combat' type rifle? Are 20" really only for long distance shooting, or are there other reasons you would pick a 20" over a 16"?

And just to confirm I do mean a real 16" barrel, not a 14.5"/1.5" setup some prefer.

What distance will you be shooting? I dont see a measurable difference in accuracy of my 16" and 20" rifles at 100 yards.

Accuracy should be the same for both.

A 16" will be lighter and more manuverable.

20" will give higher velocities and therefore greater effective range.

20" rifles are being used right now in Iraq in "urban" settings.

You may want to consider an 18" barrel, kind of best of both worlds.

I say pick which appeals most to you now for what you will normally be doing with the rifle.  You can always pick up another upper, or change barrels later.

The nice think about multiple uppers is then you can just swap depending on what you'll be doing.  Of course then why not just build a lower to go along with that upper?  And it begins....


-Hershey

You may want to consider an 18" barrel

I thought about that, but who makes one? If someone like Model 1 or J&T sold one, I would be interested.

I will be shooting anywhere from 100 to 300 yards down at the range.

Is there a significant weight difference between the 16" and 20"?

Using iron sights... go with the 20" or a 16" Bushmaster dissipator  (20" sights on a 16" barrel)

Using optics...  go with the 16"

I'd think a 16 inch barrel, stock A2 set up for an all around rifle. While flat tops look vry cool, I don't really like "detachable" sights for an "all around rifle". Flat tops most certainly have their place with the many options available, for an "all around" rifle, I like the standard A2 carry handle. It's the K.I.S.S. approach to a fine battle rifle.

20 inches isn't really "too long" but longer than necessary IMHO, 16 inches feels ideal with what is really very little compromise to accuracy.

It certainly won't hurt to build a 20 inch upper and have BOTH as switching out uppers is so easy where the effort in doing so is nil.

The 16" seems louder to me, even without a brake. Mine also shoot out a huge fireball with surplus ammo.

I like my 16" midlengths though. They are handy and not as front heavy as the 20" A2 type, but still keep a decent sight radius.

However, I did get to shoot a 20" SP1 the other day and really liked it. It didn't seem front heavy at all. The only thing I didn't like about it was the cheezy furniture. I'm really starting to consider building a 20" upper with a lightweight barrel and Cav Arms A2 handguards. Since I only shoot XM193, the 1/12 twist isn't an issue with me, but it sure would be nice if somebody made a 20" lightweight barrel in 1/9 twist.

Obviously the 20" M16A4s are getting used in Iraq in urban settings, but that doesn't mean that they're ideal for that situation.  Generally the shorter the better for indoor work, and the longer the better for outdoor.  I'd pick a mid-length 16" myself.  The mid handguard balance the look of the 16" better than the regular CAR handguards.

Most barrels are HBAR from the factory.  A 20" HBAR is 3.5lbs vs. 2.7lb for a 16" HBAR, so the weight is somewhat significant.  If you go with an M4 barrel you're down to 2.2lbs but a "govt profile" 20" is 2.5lbs so there's not as much difference if you go with the lighter profiles.  Bushmaster has a 20" in the govt. profile and you can get a govt profile 16" midlength from ADCO.  Lots of people have the M4 profile, but be sure to get one that's thin under the HGs.  Some have the notch for looks, but are still heavy under the HGs.  

I would definitely get the A3/A4 flattop.  For a GP rifle you'll probably want to put optics on it, an Aimpoint or EOTech would be good for your distances, and that's SO much easier with a flat-top.  Considering the Army and Marines are going to M4s & M16A4s with optics and detachable irons I wouldn't be concerned about the durability.

I prefer the 16" rifles for all around, but my buddy has a pre-ban DPMS 20" gov't profile rifle that is schweeet, in terms of weight and feel.  

To each his own, but for an all around rifle, I suggest a flat top...it gives you many more optics options, really, and if it's to be your only rifle for a while, you don't want to be sitting there in six months going, "damn...I shoulda bought the flat top."

One ideal setup for an all around rifle is an Aimpoint, an ARMS # 40, and a scope on ARMS mounts...you can go Aimpoint to scope in about 30 seconds, and you've got the BUIS iif you need it.  Keep the Aimpoint on the rifle, if you have to grab it quick, most likely you'll be engaging those pesky zombies closer rather than farther away...and you can keep the scope with your other essentials in your bug-out bag.    You might also look into a rail setup of some variety, to give you the option for a bipod, light, or whatever.  

Although I haven't gotten one, the Yankee Hill lightweight forend looks really cool, and shouldn't add a whole lot of weight to the rifle.  

Actually now that you mention it I am in the process of deciding what YHM free float rail system to order...Either a rifle length for a 16" dissipator or a CAR length for a carbine. Talk to BrightFlashlights, he has great prices on the forearms and is fast about responding to any questions you might have. He also has his own section in the industry board, complete w/pics. Check it out.

So as of a couple of hours ago I pretty much decided in favor of a 16" rifle. Now its a tossup between the CAR and a dissy, though I'm leaning towards dissy for extra rail options, such as a bipod and the like. I will let you know.

I've not noticed the 16" being louder really, but then again, I can't hear all that well anyway.

About the 20" SP1, what was it about the furniture you didn't like? *Nosey look*

Doesn't DPMS make a lightweight barrel in 1 in 9 twist? I seem to "think" I remember they do. (But don't quote me)

Quoted: The 16" seems louder to me, even without a brake. Mine also shoot out a huge fireball with surplus ammo. I like my 16" midlengths though. They are handy and not as front heavy as the 20" A2 type, but still keep a decent sight radius. However, I did get to shoot a 20" SP1 the other day and really liked it. It didn't seem front heavy at all. The only thing I didn't like about it was the cheezy furniture. I'm really starting to consider building a 20" upper with a lightweight barrel and Cav Arms A2 handguards. Since I only shoot XM193, the 1/12 twist isn't an issue with me, but it sure would be nice if somebody made a 20" lightweight barrel in 1/9 twist.

Quoted: However, I did get to shoot a 20" SP1 the other day and really liked it. It didn't seem front heavy at all. The only thing I didn't like about it was the cheezy furniture. I'm really starting to consider building a 20" upper with a lightweight barrel and Cav Arms A2 handguards. Since I only shoot XM193, the 1/12 twist isn't an issue with me, but it sure would be nice if somebody made a 20" lightweight barrel in 1/9 twist. Quoted: About the 20" SP1, what was it about the furniture you didn't like? *Nosey look* Doesn't DPMS make a lightweight barrel in 1 in 9 twist? I seem to "think" I remember they do. (But don't quote me)

It's just personal preference. There's nothing wrong with the triangle handguards, but I prefer the round ones. I also like the modern satin plastic of the Cavelry Arms stuff better than the shiny plastic used on the old A1 furniture.

I wasn't aware of a DPMS light weight 20". I'll look into that. Thanks for the tip.