16inch vs 20inch?

So as you may know I'm building a AR 15, well really just ready to slap a upper on it.

I've been researching 16 inch barrel vs 20 inch barrel. From what I seen on YouTube the 20 inch barrel was packing a greater punch than the 16 inch barrel AR 15s.

So my question is is this just the eye playing tricks on ms or does the 20 inch barrel really sends the rounds out hotter and faster than the 16 inch?

I am currently locked in on a 20 inch hbar upper for my lower, I would like to have the most powerful AR 15 possible so am I making the right choice on the 20 inch barrel with a 1/7 twist?

Longer barrel = longer time for bullet to exit barrel = more velocity and energy = higher risk of missing due to muzzle flip. More power with range = 6.5 Grendel. IMO, high-grain match-grade rounds out a match-grade 1:7 barrel is more important than 4" of barrel length, depending on the desired shooting distance. HBAR will likely give best results. 24" HBAR uppers are available. No perfect answer. It's all about tradeoffs.

Boom Boom said:

... = higher risk of missing due to muzzle flip...

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I have never heard this before. Please explain.

In any case, the Grendel is something the OP should look at if worried about power out of an AR15 platform. Having said that, and sticking with .223/5.56, I think the are some marginal gains with the longer barrels. I've looked into this to and have pretty much settled on a 16-18" range with heavier boolits. But as Boom Boom says, it's about tradeoffs.

Yoshi said:

I have never heard this before. Please explain.

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Lighter-profile, longer barrels tend to have more muzzle flip/rise (and whip) before the bullet exits the barrel compared to shorter barrels with the same profile. It can be compensated for with a heavier barrel and/or brake. It is most pronounced in off-hand shooting. We're not talking a lot of difference, but it doesn't take much when you're shooting hundreds of yards, assuming the ammo and barrel are otherwise up to the task.

Can the longer barrel really make you miss when it barely jumps at all? I didn't really see much if any recoil out of the 16 inch or the 20inch. But when the round hit the melon out of the 16 inch and 20inch the melon exploded when the 20inch one hit it vs the 16inch just blowing a nice chunk out of it.

I'm just trying to learn. Before I decide.

I've found my 16 inch 1-to-9 inch twist HBAR bushmaster (old bushmaster) to be as much or more accurate than my 22 inch varminter.

It regularly outshoots the longer rifle with 55, 62, and 45 grain polymer tipped varmint rounds.

That said, you do get a marginal amount more velocity from the longer barrel- but these days with the propellants they have now you really do get much MUCH more from a shorter barrel than was possible even 30 years ago.

How Barrel Length Affects 5.56x45 Muzzle Velocity
The effects of the 5.56x45 NATO ammuntion depends greatly upon its velocity at the time of impact against the target. 5.56 ammunition, if travelling at a high enough velocity, tends to fragment upon impact of a soft target. The bullet will penetrate into the body for about 4 inches, while it yaws. When it yaws, if it is travelling fast enough, the bullet cannot withstand the stress upon it, and it will fragment into many smaller pieces. These smaller pieces each travel outwards from the fracture point, multiplying the effect of the wound. The threshold for this fragmentation effect is 2700fps.
Barrel
Length Velocity (55gr M193)
Feet per second Velocity (62gr SS109)
Feet per Second Energy (55gr M193)
Foot Pounds Energy (62gr SS109)
Foot Pounds
10" 2739 2627 916 950
11.5" 2872 2738 1007 1032
14.5" 3064 2907 1146 1163
16" 3132 2989 1198 1230
20" 3259 3095 1297 1318
21.5" 3386 3185 1342 1373
24" 3315 3158 1342 1373
26" 3391 3231 1404 1437

Test shots were from a Bushmaster XM15E2 AR-15 type rifle, except for 21.5" value, which was from a Bushmaster M17S bullpup rifle.. Velocities found from average of three rifles each firing 5 shot groups, for a total of 15 shots for each value. Test conditions were: 0 degrees Fahrenheit. Barrel rifling - right hand twist, 20% of bullet length.
As one can see from the table, anything under 10" in length will not provide enough muzzle velocity to attain the best wounding capabilities of the 5.56x45 projectile. Anything lower, and the bullet will make a .22 caliber hole through the target, with relatively insignificant wound ballistics (compared to the same bullet at 3100fps). This is why short barreled weapons like the HK53 and G36C are somewhat unsuitable for CQB (8" barrels, estimated muzzle velocity around 2550 fps). There have been reports of weapons of this barrel length to be unable to penetrate soft kevlar vests, which is very worrying for a weapon of rifle caliber.
One must also contend with the increased muzzle blast from such short-barreled weapons, which can be considerable. There have been numerous police reports that officers firing short-barreled AR-15 carbines (11.5") in small rooms have come out with bleeding ears and noses. This is why one often sees suppressed 5.56 weapons - although the weapon itself is relatively loud for a suppressed weapon, the suppressor keeps the muzzle blast down to a managable level. Also, with AR-15 variants with barrels shorter than 10", it has been found that they rarely perform reliably without a suppressor or a very long flash suppressor - which defeats the purpose of the short barrel. CAR-15 carbines of Vietnam had 10" barrels; however, they also had 4 inch long flash suppressors. When a normal A1 'birdcage' style flash suppressor was used on the CAR-15's, the carbines turned into very sexy looking single shot weapons - the short barrel does not allow enough back pressure to develop, which does not allow the gas operation system to work properly.
However, a new report in the most recent edition of Guns and Weapons for Law Enforcement has a very interesting article on super-short carbines for CQB use. These are AR-15 type weapons with barrels no more than 6 to 8 inches long. Although I dismissed these weapons as wishful thinking when I first saw them, they may have a very practical use in two to three years. Special types of very fast burning propellants are under development that allow not only muzzle velocities comparable to full-length AR-15 rifles, but the same reliability as well! The new ammunition, however, does not perform well in full-sized rifles, as the powder burns too quickly for reliable cycling.

longer barrel can also lead to reduced accuracy through increased harmonics. heavier barrel as well as surpressors reduce the harmonics.

Boom Boom said:

Longer barrel = longer time for bullet to exit barrel = more velocity and energy = higher risk of missing due to muzzle flip. More power with range = 6.5 Grendel. IMO, high-grain match-grade rounds out a match-grade 1:7 barrel is more important than 4" of barrel length, depending on the desired shooting distance. HBAR will likely give best results. 24" HBAR uppers are available. No perfect answer. It's all about tradeoffs.

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Grendel=more expensive rounds + more time trying to find ammo + settling for what ammo is available + less demand for your upper if you decide to sell.

Like you said , its all about tradeoffs

I have a 20" WOA upper on order.... in the mean time my father picked up a $400 1/7 pencil barreled upper from PSA, with a 1-4 scope and 55gr PMC, we sqeaked out a little over 1 MOA (would have been a touch under but 1 out of the 5 shots was a flyer).

Both will do the job at 100 yards, one will be much heavier than the other...but at the end of the day, what are you looking for? That makes a difference in your decision.

The quality of the barrel is of greater importance than the length when comparing 16-20"...

What do you want this AR for? Do you want it for long range target shooting? Do you want to use it for Home Defense? Do you want to have it for SHTF? Depending on what you're going to be doing with it will depend on what barrel length you should go with.

sailskidrive said:

The quality of the barrel is of greater importance than the length when comparing 16-20"...

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Yep.

Accuracy between 16" and 20" barrels from a single manufacturer using the same ammo should be identical. What little extra velocity you get with an added 4" of barrel is minimal. The only real advantage to the longer barrel is slightly less bullet drop at long distances, and a longer sight radius if using irons. The later will definitely affect your realistic accuracy.

Check out this article that someone posted recently. It is not the end all be all, but it talked me out of a 20". http://www.thetruthaboutguns.com/20...t-barrel-length-muzzle-velocity-and-accuracy/

Overboost44 said:

Check out this article that someone posted recently. It is not the end all be all, but it talked me out of a 20". http://www.thetruthaboutguns.com/20...t-barrel-length-muzzle-velocity-and-accuracy/

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Experienced AR-15 shooters have been demonstrating for years that the AR-15 platform benefits little if any in most situations from a barrel longer than 16-18". It has been shown numerous times over that a longer barrel can degrade accuracy due to muzzle rise and barrel whip. Especially with a standard-profile or lighter barrel, 20" or longer makes no sense within the useful range of most 5.56/.223 rounds. It especially makes no sense for surplus/bulk ammo.

There are mostly certainly a few benefits that a 20" has over a 16".
-Rifle length gas systems are much easier on bolts and generally more reliable (Midlength mitigates this to some extent).
-Reduced muzzle blast
-Longer sight radius

I have few 16"s, a couple 18"s, and a few 20"s. the 20"s are very pleasant to plink with on the range. Both are plenty accurate.

ObsceneJesster said:

What do you want this AR for? Do you want it for long range target shooting? Do you want to use it for Home Defense? Do you want to have it for SHTF? Depending on what you're going to be doing with it will depend on what barrel length you should go with.

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For home defense and shit hits the fan. Probably a few times a month at the range.

Thanks for the opinions though.

I think I just might have to go with the 20inch. The way that melon exploded when hit from the 20inch vs the 16inch was very telling. I suppose if I ever want to shorten it it wouldn't be hard to just swap barrels?

go with a 16"

theres no reason for a 20" unless its a pure long range or just range toy...

imho theres a reason why you dont see newer military rifles using longer barrels unless its dedicated for a DMR or SAW type role

atblis said:

There are mostly certainly a few benefits that a 20" has over a 16".
-Rifle length gas systems are much easier on bolts and generally more reliable (Midlength mitigates this to some extent).
-Reduced muzzle blast
-Longer sight radius

I have few 16"s, a couple 18"s, and a few 20"s. the 20"s are very pleasant to plink with on the range. Both are plenty accurate.

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I guess that's the perfect way to have it lol. Just own them in all sizes.