AR15 Barrel Length Study

[Dave DeLaurant]

FYI for inquiring minds, a free online publication dating from last summer from Small Arms Defense Journal:

Barrel Length Studies in 5.56mm NATO Weapons – Small Arms Defense Journal

sadefensejournal.com

 

[jmorris]

Have a cliffs notes summary?

 

[General Geoff]

Cliff notes: short barrels suck for muzzle velocity, gas operation reliability, and effective sound suppression with silencers

 

[troy fairweather]

I'm guessing they used a new barrel. Barrels speed up after a few hundred rounds, I wonder if that's the little bump in speed that they got at 11". Did they say how many shots were fired. Be interesting to compare a rifle with a 20 barrel with a muzzle device and one with a sorter barrel but with a suppressor with the same oval length.

 

[jmr40]

Cliff notes: short barrels suck for muzzle velocity, gas operation reliability, and effective sound suppression with silencers

Needs context.

By short barrels if you mean under 10" then yes. Most civilian AR's have 16" barrels. They found max velocity at 20". They did show slightly less with barrels longer than 20" but since they used a different rifle and barrel for that phase of testing the numbers are suspect.

Between 16" and 20" they saw about 150 fps loss, but speeds were still acceptable. 14" is where most military AR barrels are. They still have enough speed to get the job done.

A chart from the article

 

[earlthegoat2]

If you are one of those people who say suppressors are too expensive for what they are, you owe it to yourself to read that article.

The barrel length discussion was interesting but really didn’t tell me anything I didn’t already know or could infer. However, the suppressor additions were quite insightful pertaining to materials and construction.

 

[zeke]

Have a cliffs notes summary?

Shorter barrels can reduce velocity significantly, while raising exit pressure significantly. If using a short barrel , consider a round other than M855. Beware of using a lightweight suppressor on a short barrel.

Am not experienced to know what the effect was of not having a gas port was, if i read the article correctly.

 

[Txhillbilly]

I'll stick with 18" & 20" barrel's. I prefer to have a rifle length gas system on any AR platform anyway.

 

[DMW1116]

Happiness is (or includes) a 77 grain Mk262 from a 20” barrel.

 

[Charlie98]

However, the suppressor additions were quite insightful pertaining to materials and construction.

To attempt to preserve sound reduction performance, a suppressor will need to be longer (and heavier) with a shorter barrel, negating most of the compactness gained by barrel shortening.

It's not quite a zero-sum game, but very nearly so. It's always been the trade-off between barrel length and practicality... sacrificing bullet energy for a more compact weapon.

 

[zeke]

To attempt to preserve sound reduction performance, a suppressor will need to be longer (and heavier) with a shorter barrel, negating most of the compactness gained by barrel shortening.

It's not quite a zero-sum game, but very nearly so. It's always been the trade-off between barrel length and practicality... sacrificing bullet energy for a more compact weapon.

Another way they could have worded it is a 10.5 in ar with a silencer can be about as short as a 16 in AR, and MUCH quieter. Of course you lose substantial velocity.

 

[Gordon]

Well for me it comes to same coclusion as I have that the hassle free 16" with or without suppressor is about optimum. I came to that conclusion before 1980 with my Colt CAR 15 SP1 . I never liked any barrel on an AR below 11+" and the 16" non NFA barrel seems perfect for field use. I have longer barreled ARs (20") for Varmints/Target an a 11.5" suppressed NFA one for around the home for years . But Most useful all around are the good old 16" ones. Which makes a lot of sense !

.300 BO gets away with shorter barrels ! .450 BM or .458 Socom seems to do very well in 12-14" . .308 AR10s work best in 18" for me and the 6.5 C in 20"

 

[InTheSwamp]

223/5.56 - 16"
308/7.62 - 18"
6.5 CM - 20"

Those are my "sweet spots". Yours may be different.

 

[Bronco72]

I have two uppers ! Both have 24" bull barrels and the gas port is closer to the muzzle than usual! One for 77ge and less and one for the heavies in 223. I get a lot of extra velocity. They were built for as much accuracy and velocity as i could get. Varmint guns they are ! Not of carrying around the country side.

 

[berettaprofessor]

Now this is why I come here! Great information OP!

 

[Charlie98]

Well for me it comes to same coclusion as I have that the hassle free 16" with or without suppressor is about optimum.

To that I would add '...with a mid-length gas system.' I think the carbine-length gassers work well enough, I don't know how well they work with a can, but for my money I'll take a 16" middy. In fact, all my 16"ers are mids.

I never did play the 'AR-pistol' game with a sub-16" barrel... never saw the need. No legal ambiguity there, either.

 

[Mosin Bubba]

18" is the sweet spot for AR barrels IMO. You get the rifle-length gas, you get almost all the velocity potential out of your small bullet, and you keep the whole package at a carbine size.

Militaries the world over like to use the 5.56 in all kinds of 13", 14" type AR derivatives. I understand that choice for logistical reasons, but if I was starting with a clean sheet of paper, I'm picking a different cartridge for those small arms.

 

[Charlie98]

but if I was starting with a clean sheet of paper, I'm picking a different cartridge for those small arms.

I think that thought has occurred recently to the Army as well... but probably for different reasons.

 

[jmorris]

Shorter barrels can reduce velocity significantly, while raising exit pressure significantly.

Another way they could have worded it is a 10.5 in ar with a silencer can be about as short as a 16 in AR, and MUCH quieter. Of course you lose substantial velocity.

I can't argue with any of that, a short .223 has a job to fill with me but the velocity hit is pretty big.



I can still make 300 yards hits with my 10.5" but its not much more powerful than a 22 magnum is at the muzzle out that far. Not what I'd pick for many situations but does make a handy gun to have around the farm.

 

[mavracer]

I can still make 300 yards hits with my 10.5" but its not much more powerful than a 22 magnum is at the muzzle out that far. Not what I'd pick for many situations but does make a handy gun to have around the farm.

Switch from 55s to 77s and you have about the same if not more retained velocity and close to double the energy.

Another way they could have worded it is a 10.5 in ar with a silencer can be about as short as a 16 in AR, and MUCH quieter. Of course you lose substantial velocity.

My 12.5" with a Griffin taper lock mount and a 5" suppressor is actually a smidge shorter than a 16" with a bird cage. No it's not anywhere near quiet, it's significantly quieter than an unsuppressed 16"