I currently have a custom build with a 16" barrel. I found out I mainly use this rifle to shoot coyotes and rabbits at 200+ yards. A lot of my buddies said I should upgrade to a 20" barrel to have more accuracy. Is 4" of barrel going to help me that much? I am happy with my 16" but will a 20" make that much of a difference?

It could improve velocity easier than accuracy. You likely don't need to go longer.

yes. when shooting small critters at long range, it's way easier with more velocity. that's why varmint guns have 24" barrels, you can make hits out past 500, WAY more difficult(borderline impossible) with a 16". get a 20", you'll have more fun and success.

No

AR's are capable of excellent accuracy. If you have a gun that shoots over 1 moa with match ammo and handloads then the barrel may be the issue, and it may be worth it to swap. But if you already get excellent accuracy out of your set-up then it is not going to help to change the barrel. It may only be worth it if you are shooting at extended ranges or shooting enough shots that heat build-up affects accuracy.

Other things you might want to consider before changing the barrel is going to a better trigger or adding a Free Float...

velocity yes.  accuracy, no.

This

Yep.

At 200 yrds you could use a 10.5 and make accurate hits.

Personally, no. If you can hit a coyote at 200-300 yards with a 20" barrel you can do the same with a 16" barrel (assuming all other factors remain constant).  Spend the money practicing, or on optics or a  quality trigger.

Just get a 20" and be done with it; you'll end up wanting another 16" AR.  This would be one of the many hazards of BRD...  

You will get more muzzle velocity with a 20" over a 16".

Which will mean the bullet will spend less time going from 0-200 yards.

Which means the time wind and gravity affect the bullet's flight path will be less.

Some (actually, a lot of, it seems) people erroneously think this makes a longer barrel "more accurate". While it can be considered an advantage, it's either to mask the lack of ability of the shooter to properly produce an accurate firing solution or decrease the amount of hold over needed to make a precise shot. Mechanically, however, the longer barrel isn't intrinsically more accurate. Infact, a shorter barrel is more rigid than a longer one with the same contour.

Unless you're making a jump in overall quality with the change, I wouldn't spend the money to change the barrel out if it's only the difference of changing the holder over due to muzzle velocity of 4" of barrel (which is typically, but not absolutely, around 200 FPS). That isn't going to be a huge change at 200 yards. Like less than an inch in both drop and a 10mph crosswind or something like that.

going with a 20" could make your accuracy better, only if your accuracy in your 16" isn't any good....or the 20" could be less accurate than your 16" (if you by a cheapy)
Like most said, barrel length doesn't determine accuracy but it does determine velocity. The further out you shoot, velocity starts having an impact on your accuracy...so yes in theory a 20" can be slightly more accurate than a 16" barrel once you get way out there in distance. If you are shooting heavy bullets like a 77gr then the longer barrel will help push it faster

You can lose about 150-200 fps out of a 16" vrs 20" barrel.  But it really depends on bullet weights and powder used.


16" barrel @ 3000 fps = 3.5" drop at 200 yards

20" barrel @ 2800 fps = 4.3" drop at 200 yards.

This assumes 100 yard zero. 60gn bullet, .255 BC

I don't claim to be an expert on this issue at all, but can some here tell me this.  Why are most all hunting rifles over 20"?  I hunt with my .243 and .308 AR's...both with 20" barrels.  My .308 bolt rifle is a 20" barreled Savage hog gun, and my .243 Ruger bolt gun is 22".  Now, while you see some short barreled bolt rifles, they're most often threaded barrel bolt guns with suppressor intent.  Are most all bolt rifle manufacturers out of touch or is there a substantial benefit to a longer barrel for ballistic performance.  And on the issue of velocity and accuracy, I reload .308 and .243.  A lack of velocity can often result in a lack of accuracy as your target gets further from the gun...obviously...while I recognize that "hot" bullets possessing extreme velocity don't always result in good accuracy just because the bullet will reach a further distance.  All bullets, powder, barrel length, and twist have to come together to make for the best accuracy, but I see more of a pattern of accuracy overall with longer barreled rifles and apparently so do most bolt rifle manufacturers.  If I'm missing something here, I don't claim to be an authority on this.

IMO, it's mostly tradition. Some rounds benefit more than others from longer barrels, but there was a time not too long ago where your 20" 308 bolt gun would have been considered too short by the hunting crowd.

Because people have trouble discerning precision vs accuracy both in regards to the shooter and the rifle.

True, all other things being equal, a faster bullet spends less time in the air over a given distance for environmental factors to affect a bullet's trajectory. It also increases the range at which a bullet goes sub sonic, which for most bullet designs ends the practical range of precision fire. On an AR-15, a longer sight radius also helps a shooter to be more accurate. People then sum this up to a longer barrel being more "accurate".

In effect, that simply means that shooters tend be more accurate with a longer barrel (due to increased muzzle velocity) because wind and gravity simply have less time to do what they do to a bullet in flight so any unaccounted drop or wind drift will have less of an effect on the point of impact from the point of aim. It's certainly an advantage like a better ballistic coefficient. Though it has nothing to do with the mechanical precision of the barrel, it's ability to fire the bullet in a consistent manner. Infact, the shorter barrel of the same contour will actually be more rigid and more precise due to a lessened effect of harmonics/whip.

Saying a longer barrel is more accurate is, well, inaccurate - or at the least not the whole story. People have been cutting barrels for years to show this myth is nothing more than bad semantics of fudd-lore. Here's one article. And another. Some more. Again.

For OP, as long as he is accounting for wind and drop correctly anyways, he'd notice no difference in his precision at 200 yards, unless the barrel he gets is of actually higher quality. People then start banging on about 500 yard accuracy as a great reason to get a new barrel

But then again OP didn't really swamp us with info about his setup, ammo, or optics anyways

DNC1982, those were great links with some excellent info.  I guess it does seem to hinge more on the particular bullet, powder type/charge, and even caliber to some degree.  Looks like there's a pattern that larger caliber rifle bullets do a little bit better generally with a longer barrel...to a point.  Their comparison of the .308 to the 300 Win Mag kind of points that out.  The bigger case volume to push bigger bullets seems to need some "minimum" barrel length to burn that powder for most velocity effect on the bullet.  There doesn't seem to be an absolute formula for this, but it seems apparent that some/many calibers don't require that longer barrel scenario to achieve maximum performance.  Fascinating stuff.  I recently got one of those Kel-Tec PLR16 5.56 plinker pistols...a really fun, hoot-to-shoot firearm.  This is the only 5.56 gun I own, as my AR's are .243 and 7.62.  I find it amazing how accurate that 9.2" barrel on that 5.56 pistol can be.  The 5.56 cartridge seems to be one of those bullets that still performs quite decently with a relatively short barrel.  So I guess it comes down to how/where you're using a weapon of any given caliber.  Long range target or hunting will not equal "house clearing" in a SWAT scenario, so whatever compromise one makes in their barrel length decision will apparently not be an absolute one-size-fits-all.  Still, it appears that really long barrels aren't the holy grail of performance that they were once perceived.  Thanks for posting those links/studies.

http://www.thetruthaboutguns.com/2013/10/daniel-zimmerman/the-truth-about-barrel-length-muzzle-velocity-and-accuracy/

There's a lot of good info in here regarding Accuracy, but what he is really asking is "will I be able to hit my target easier with a longer barrel" and the answer is yes.

He's shooting  coyotes and rabbits at ranges of 200 PLUS yards. He didn't quantify PLUS, but I assume that means at whatever range they could see them. People regularly shoot varmints out past 500 yards. At 200 the difference is negligible but as the distance increases the difficulty in compensating for ALL factors(including, ranging errors, change in elevation, change in wind, temp, muzzle velocity) and still making first shot hits increases as velocity decreases.

OP, you will be able to hit coyotes and especially rabbits easier with a 20" then a 16" barrel, especially as range increases.

A better question is, Why limit your capabilities with a shorter barrel?

The better question is get both

OK lots of things here, let's go one at a time...

Barrel length and accuracy have little to nothing to do with each other.  Barrel length strictly gains you velocity, therefore getting your projectile onto target faster, and with a longer reach.  The force of gravity being a constant the bullet, if fired parallel to the ground, will always take the same amount of time to fall to the ground.  Faster bullets go further before this happens.  On the other hand if "200+" is assumed to be out to maybe 300yds your 16" barrel is fine from a velocity standpoint.  If you need accuracy that is a manufacturing issue and a high-quality barrel, even another 16" will help that cause.  Better trigger and making sure the barrel is free-floated add to accuracy, but the finger on the trigger and how good it is matters most.

To determine whether or not you need a 20" is based on one thing, do you reload?  Factory 5.56/.223 ammo gets a complete powder burn around 18" of barrel length.  This means that the acceleration curve starts dropping once the powder is burned up.  If you reload, using slower powders, then you can make use of the full 20" of barrel, but with factory loads there is only about a 30fps difference between 18 and 20", but about 200 fps difference between 16 and 18".  In other words with factory ammo 18" of barrel will give you essentially all your velocity.  If you reload you can get more with a 20+ inch barrel, if not reloading you're wasting you're energy hauling 2 extra inches of steel around.  The military saw this when they developed the SPR; they realized that the 2 extra inches did nothing for them, hence the match-grade 18" barrels.

Someone asked why traditional hunting rifles are typically 20+ inches.  The answer is the same as above; based on the amount of powder and the powder burn rate you need the bullet to stay in the barrel long enough to reap the benefits of a full powder burn.  Full burn = velocity = longer effective ranges.  This is why one would choose a magnum, more powder to burn means extended ranges.  A perfect example of this was the need of the US military to extend their ranges to that in-between area of what the 7.62 x 51 could not do but the .338 Lapua could.  This is what brought along the decision to go to the 300 Win Mag, faster (same .30cal) bullet means extended range.  To get all the benefits though you have to have enough barrel to burn the powder.  This is why many magnum rifles are 24-26" in length.  My .270 WSM is a 26" barreled Remmy 700, spitting a 130gr OTMBT at over 3300 fps.  As seen in the automotive world there really is no replacement for displacement.

Soooooo.... factory ammo only?  No change or 18" is plenty.

Reloading?  Hell go to a 24" and be all you can be.

Ultimately good barrel + FFHG + good glass + good technique = good hits.

I have a patrol rifle with a 20" A1 barrel and forearm. I did it partly cause Im used to full size hunting rifles and partly cause I like to remember my old A1 from the '70s. Its a sweetheart of a shooter and extremely accurate.

I dont think theres any doubt such a set up will improve long range accuracy but probably not to a very noticeable amount. It comes down to the shooter, but if your a serious 'yote hunter it might be worth a look.

The accuracy and velocity debate goes hand in hand. Accuracy will reflect better with faster rounds since the drop doesn't have to be compsenated as much. But given the base line distance you'll need to retrain or re zero. But we're talking about longer distances than 200 yards. At 200 yards you won't notice that big of a difference.

Accuracy is a reflection of consistency.

This^^

I enjoy tipping over coyotes and other little critters and run with some others that do as well.  

Let me ask you this.... how does your 16 shoot ?

If you and your 16 inch gun with the custom barrel are capable of shooting MOA or better on paper at 100 ..... you have plenty of gun out to 400 (and probably then some - but you will get more runners and less doa's the further out ya go) ....and your misses aren't caused by the bbl length.  

Maybe you just need some more practice at that range and experience with wind.....not many no wind days in my neck of the woods.   A good wind will move the bullet more than the diff between bullet drop in a 16 vs 20 on many days.   Maybe you need a more accurate round in your rifle .... even with a 20 or 24 inch barrel .... the gun/ammo/shooter will still need to be pretty accurate to hit the kill zone of a coyote at 400.   A LOT more people talk about than can actually consistently do it....regardless of what they are carrying.    

You'll drop more fur if you can figure out how to hit runners at 100-200 than standers at 400 anyway....and if you find they are consistently sitting out there looking at you at 400 and not coming closer ...you need to change your set up not your rifle imo....but you can work on that after ya drop em  

No offense intended...but maybe your buddies are  simply questioning the overall accuracy of your custom 16.
     

Short and thick for accuracy, assuming good ammo and barrel.

Length adds velocity

18" SPR is about perfect imho

Longer will improve velocity more so than accuracy. With a scope shorter is more accurate.

This.

the extra velocity doesn't make the barrel more accurate but it does can make it easier for the shooter to be more accurate at longer ranges...imo

The OP vanished