AR Barrel Length

[Slick]

I know there are a lot of AR owners out here, so I thought I'd seek help (Hey, my wife always tells me to seek help, so...) . I just can't decide what barrel length to get on my AR15, 16" or 20". What are the advantages or disadvantages of the different lengths? Does the 16" heat up faster?

I like the look of the rifle with the 20" a little better, but the 16" feels a little better balanced (not so heavy up front). HELP!!

I'll primary use it at the range, and to execute those critters who are so bold as to do damage to the horse pasture. Since it will be in my home, I suppose HD is a remote possibility.

Thanks,
Slick

 

[Nightcrawler]

I prefer 20". But then, I've never handled and HBAR-15, only M16A1s and A2s. As I understand it, virtually all commercial 20" ARs have barrels heavier than even the M16A2, and that's why they're muzzle heavy. You get much better ballistics out of a 20".

 

[Rob96]

The ballistics are better out of a 20" barrel, but you get everything you need out of the 16".

 

[Kentucky Rifle]

My Bushmaster "Shorty" has a 16" HBAR.
A 20" AR would be difficult to carry behind the seats of my truck. At two or three hundred yards, my 16 incher is very accurate.

KR

 

[COHIBA]

it depends on your rate of twist. a 1/12 twist in a 20" will give you 1.6666 rotations from muzzle to crown. a 1/9 twist on a 16" will give you 1.777 rotations.
if you plan on using fairly light, 55gr, bullets then a 1/9 twist on a 20" is gonna over spin your bullets and may cause some core/jacket seperations in hot loads.
regardless of the BBL length you should do yourself a favor and look at the BM dissapator model. it carries a 16" 1/9 twist w/ full length handguards. most importantly the sight raidius is full length thus giving you a huge advantage over a carbine when using iron sights.

 

[curt]

bullets then a 1/9 twist on a 20" is gonna over spin your bullets and may cause some core/jacket seperations in hot loads.

WRONG! WRONG and WRONG.

Having said that i like the 16" barrel for close in stuff since as you noticed it is quicker to point and less likely to tangle. The 16" barrel doesn't really give up anything ballistics wise until after ~200 yards. However it sounds like HD is lower on your priority list than range and varmint use. If thats the case you'd probably be better served by going with a 20".

 

[TechBrute]

most importantly the sight raidius is full length thus giving you a huge advantage over a carbine when using iron sights

Also, it uses the full length hand guards so the gas tube is longer, theoretically increasing the reliability.

 

[Redlg155]

Also, it uses the full length hand guards so the gas tube is longer, theoretically increasing the reliability.

The Bushmaster Dissapator gas tube is in the same location as the gas tube on a 16" rifle. The gas block is milled so it can fit under the handguards and a FSB installed at the full length HG location.

However, the mid length rifles such as the Armalite and Rock River have a longer gas tube.

This could be another consideration for a 16" barrel version. The handguard is longer and the barrel doesn't look as long, giving it a more balanced look. The sight radius is also longer than a standard 16" version, but it doesn't have the "snubby" look of a Dissy.

Most folks have seen this pic before, but to give you an idea, this is a 16" mid lenth with the barrel cut to 14.5 and a KKF muzzle brake attatched. It's in 9mm, but the .223 looks the same except for the smaller exit hole of course.

Good Shooting
Red

 

[Onslaught]

WRONG! WRONG and WRONG.

Care to explain WHY he's wrong, or are you just gonna yell that he is wrong without backing it up?

I second the vote that you take a look at the "mid-length" handguard versions by Rock River or Armalite. To me, they just LOOK better than the regular carbine version (and this coming from a guy who has a "shorty", so not an insult). Since you like the look of the 20", and these are designed to be more proportionally similar to the 20", you may like them. (see bottom "green" rifle)

 

[Jim Watson]

Just to be Different

I bought one of those Colt CAR A3 24" heavys. I soon found I didn't need an automatic benchrest rifle and saw no need to hump around a ten+ pound .223. So I had the barrel cut off to 18.5" and turned to A2 profile. Why 18.5" you may ask? Because that was as short a barrel as I saw anybody (JP) using a rifle length gas tube on. It functions reliably and is still as accurate as it was with the barrel at the original length and diameter - under MOA with good loads.

 

[curt]

Care to explain WHY he's wrong, or are you just gonna yell that he is wrong without backing it up?

the second choice

 

[Redlg155]

This is from the Bushmaster Firearms Website concerning barrel twist rates.

Q. Which rifling twist rate is best for AR-15 rifles? I've seen all different rates: 1 in 7"; 1 in 8.5"; 1 in 9" and 1 in 10". What are the advantages to all the different twist rates?

A. The optimum twist rate for you will depend entirely on the bullets you shoot and what you want them to do. We have found that a 1 in 9" twist rate will utilize all commercially available ammo and wear longer than the Gov't. mil. spec. 1 in 7". The first gov't M16's were done 1 in 14" and then the M16A1 was rifled 1 in 12", but these rates are rarely offered these days (we live and learn!). Some sporting rifles have been made with 1 in 10" and some AR makers offer this barrel but it won't be chrome lined. The 1 in 8" or 1 in 8.5" barrels will stabilize the super-heavy (80 gr.) bullets, but these are for very long distance competition shooting and are not chrome lined. When properly handloaded, these heavy bullets are too long to function in magazines and must be inserted into the chamber one shot at a time. The 1 in 7" barrel was a military development created to stabilize a long tracer round but it is too fast a twist for some of the lighter bullets (40 - 50 gr.). We have heard of cases where this centrifugal force caused a lighter bullet to explode after leaving the muzzle. Again, the 1 in 9" chrome lined is the best and longest lasting compromise we have found, and will shoot well with bullets anywhere from 40 to 75 grains in weight.
---------------------------------------------------------------------------------

Good Shooting
Red

 

[Matthew_Q]

The deal about twist rates and bullet weights is NOT how many rotations the bullet makes INSIDE the barrel, it's how FAST it's rotating when it exits the barrel.

A faster twist rate is better for LONGER bullets. Longer bullets in .223 generally tend to be HEAVIER, so it's thought that faster twist is better for heavier bullets. True, but not quite BECAUSE a bullet is heavier.

1:12 is great for 55gr or lighter, as they are smaller and shorter. I had a bolt rifle with that twist that LOVED the Winchester 45gr white box stuff.

1:9 Should work great for 55gr ball, and should do ok on 62gr pills.

1:8 better for 62gr, might 'overstabilize' lighter bullets, and for REALLY light bullets, the fast spin/centrifugal force, is sometimes enough to throw the jacket off of the bullet as it flies.

1:7 Better for the heavy stuff. 70 grain and up.


(the above are just my opinions in my experience. I am probably not 100% correct, but I should be generally in the right ballpark with each)

 

[ocabj]

You should get a 20". It serves most range purposes.

I personally have a Colt Sporter HBar Lightweight Pre-Ban in 16". It's a great balance of power and size. But it's strictly relegated to range time. I would never use it for typical home defense. So a 16" doesn't give me any real life advantage.

Get a 20" without a flash supressor and it will give you a good paper puncher. If for some reason you eventually want a 16", you can always get another upper receiver. I've been meaning to get a 20" flattop upper but I've always had other expenses preventing me from doing so.

 

[Onslaught]

The deal about twist rates and bullet weights is NOT how many rotations the bullet makes INSIDE the barrel, it's how FAST it's rotating when it exits the barrel.

Thank you. That's all I wanted... Facts to back up an opinion, one way or the other.

But I do have one question (and it's making my head hurt trying to hang on to this concept)

A rifle's twist rate denotes the distance a bullet would need to travel inside the barrel to complete a single rotation... In the case of the 1:9 twist a bullet rotates 1 full turn in 9 inches. If a bullet is traveling 3300 fps, it is going spin faster than a bullet going slower, although the twist rate is the same... right?

SO, (ouch, my head) If a 16" barrel produces a muzzle velocity of 3132 fps, and a 20" barrel does 3259 fps... Then a bullet fired from a 20" barrel with a 1:9 twist would be spinning FASTER than the same bullet fired from a 16" barrel with a 1:9 twist... right?

 

[Jim Watson]

Right.
Just divide the velocity in feet per second by the twist pitch IN FEET and you get revolutions PER SECOND. Multiply by 60 for rpm. In your example, 3132 fps / .75 ft twist x60 = 250,560 rpm. and in the 20", 3259/.75 x 60 = 260,720 rpm. Don't get all excited, that bullet isn't going to be traveling for a minute.

And, as I recall, bullet stability gains only by the fourth root of rpm. The 20" spins the bullet 1.0405 times as fast, but it is only 1.01 times as - 1% more - stable.

 

[COHIBA]

dang jim, you made my nose bleed.

 

[bad_dad_brad]

Barrel length of an AR sort of depends on it's primary function. I wanted a quick handling well balanced HBar, so I chose a 16" Bushy shorty. Works for me. The 16" length is a good compromise between a 20" and a 14. Besides, legally, the citizen can not own a 14" without a comp which makes the barrel 16" and very LOUD! So what is the point.

I plan on getting a 24" varminter upper in the future. I chose the 16" for it's handiness.

 

[T.Stahl]

Light bullets out of a long barrel with a fast twist can't be that bad.
My SL8 has a 20" barrel with a 1 in 7" twist. In the manual HK recommends 52gr Sierra MKs...