Optimal Barrel Lenght For AR-15

[Bart Solo]

I have been giving some thought to building a dual purpose AR-15 upper for multi-gun and home defense. The rifle needs consistent accuracy out to several hundred yards while remaining light and handy enough to deal with short range targets. Of course, every inch of a barrel adds weight and makes it less handy. For legal reasons 16 inches is the shortest barrel length allowing me to swap out compensators.  To go shorter the muzzle break or flash suppressor has to be permanently fixed to the barrel so the over all barrel length is always 16 inches. One of my friends says I should use an 18 inch barrel to gain maximum multi-gun versatility. Will I lose much long range accuracy if I use a 16 inch barrel rather than longer barrel?  I have been wondering how long a 223 barrel needs to be to obtain maximum powder burn.   
 
 
 
 

[mcwoodduck]

I like my 20".
I have a fixed stock, and fixed sights the sight radius is good  and the over all length is 1" longer than my tiny M1Carbine.

[Lloyd Smale]

I like 16 for its handiness. But its marginal for getting enough velocity for reliable expansion of some bullets out past 200 yards. if varmit hunting is part of the use for this gun. Id consider a 20 inch gun. As to just accuracy. Ive got a couple 16 inch guns that shoot moa and even one that will do about half that with loads it likes so barrel lenght has very little to do with accuracy.

[Gene R]

It has been proven that shorter barrels are generally more accurate than longer barrels, but you will suffer from loss of velocity. How ever, human eyes (mine at least) are more accurate with longer barrels if using iron sights, if you use optics then you can go shorter.
But at 200 yards, I'm not sure if you will loose enough velocity to make much diffrence unless you are hunting and that is where velocity rules.

[Bart Solo]

I am wondering where I can find out just  how much velosity I loose at 16 inches over a 20 or 18 inch barrel.  There have been tests of .308 barrels showing no significant velocity loss down to 18 or 20 inches from the classic 24-26 barrel length, but I haven't seen anything on the 5.56 (223). 
 

[Gene R]

To know for sure out of your barrel you will need to use a chronograph. But as a rule of thumb we generally consider about 50fps lost per inch. Federal shows their 55gr fmj at 3240fps and 2536fps at 200 yards, and 2222fps at 300 yards out of a 24 inch barrel at the muzzel, so a 16 inch barrel should be roughly 2840fps or so at the muzzel. The rate of twist plays a small effect on velocity as well, but not much.
 
Again the only way to be positive is use, buy/borrow a chonograph and test the load you plan to use.

[cjclemens]

I did a little testing on this just out of curiosity.  With several different brands of store-bought ammo, I saw no measurable decrease in 100 yard accuracy.  I saw almost exactly 200 fps loss in muzzle velocity in the 16" barrel when compared to the 20".  That's not enough to affect performance at 100 yards.  Anything beyond that would require further testing.  That being said, 100 yard performance is reasonable to expect from a versitile, multi-purpose rifle, but regular use at ranges over 100 yards almost begs the use of a 20" barrel.

[mcwoodduck]

Go to your local shop and see what you like.
The cool thing about the AR is it is modular.
You can pull two pins and change out the top from one upper to another.
and go from caliber to caliber.  Length to length.
Multiple uppers can be had for special jobs.  24" flat top floated handguard with a mounted 6-24 scope in 204 Ruger or 223 if varmint hunting is on the list.
A 16" flat top with a mounted light and a red dot for the house if you want in 45 acp or 9mm.
Then comes the whole custom.  Changing out handguards, adding rails, sights, and on and on.
The AR 15 is leggos for adults.  a sports car can become a drag racer in short order or to a sports sadan.
On Shooting Gallery the other day they were showing an AR that had a interchangeable mag well.
And at the time they had it so you could go from AK mags to AR but it would also allow you to go from 223 to 308 or down to pistol and take your favorite pistol mag.  How cool would it be that your AR for the house take the same pistol mags as your handgun.  i would want one that shoots Sig mags and may even buy a Glock if it only took Glock mags.

[Lloyd Smale]

as to a 308 my 16.5 inch ar10 is about a 100 fps slower then my 18 in model 7 and about 200 fps slower then my 22 inch ruger with 150s the ar is suprisingly the most accurate of the 3 though.

[KansasPaul]

I just went through a similar decision process myself. My goal was to have a light weight carry rifle that would serve as a test mule for my reloading habit, it would serve as a varmint gun (so it had to be accurate with provision for mounting a scope), and all-around plinker.  It also had to be small enough to fit in a small space in my car - meaning it had to have a 16" barrel.  I planned to shoot out to 300-350 yards.  I decided to go with a rifle with 1/7 twist so that I could shoot heavier bullets, which retain energy, at the ranges I planned.  I bought a Colt 6940 upper and mounted it to a Noveske lower that I built.  I like the monolithic upper on the Colt because of the solid optics base it provides.  I'm not suggesting that you buy a Colt, but you might want to consider a barrel with a faster twist than the standard 1/7.  I'm pretty sure that RRA makes an upper with a Wylde chamber (still allows shooting of .223 and 5.56 ammo - but closer tolerance) and 1/8 twist.  I'm pretty sure that RRA claims 1 MOA for that configuration.

Blessings

Paul