Barrel Lengths

[fj#316]

Can anyone explain the pros and cons of the different length barrels.
From the 10.5" on up.

[K.L. Davis]

Assuming you are talking about regular old 5.56mm ammo...

Muzzle velocity falls off as barrels get shorter, this decreases rapidly when barrels get shorter than 16-18 inches.

Shorter barrels are more manageable in close quarters and vehicles.

14.5" barrels exist to mount the bayonet to a rifle with the carbine gas system.

Barrels less than 16" OAL are an NFA item, 14.5" must have an extended and permanently attached flash hider in order to not be an NFA device -- extending a barrel less than 14.5" to be 16+ OAL is just silly.

16" barrels on a carbine length gas system have excessive dwell time for the port pressure, this may or may not be a concern of yours.

Any barrel over a foot long or so will be accurate enough for most needs.

Shorter barrels *look* cooler.

Owners of registered SBRs should be aware that if they are charged with a crime while in posession of the weapon, they could be subject to very harsh punishment under current federal laws.

Unless you have to mount grenade launchers and such, a 16" barrel with a mid-length gas system is very, very hard to beat for an "all around practical" rifle.

[UVvis]

The shorter barrels are also louder given the same flash hider.

The shorter gas systems also feel like they have a sharper and more violent operation.

[Aubrey]

...16" barrels on a carbine length gas system have excessive dwell time for the port pressure, this may or may not be a concern of yours....

K.L.,
Would you please elaborate on this statement? I'd be much obliged to understand this better.

[graffex]

K.L.,
Would you please elaborate on this statement? I'd be much obliged to understand this better.

I'm also curious as to what exactly that means.

[Hoplophile]

For one thing, a longer dwell time means a shorter time between the bullet leaving the muzzle and the bolt opening far enough for gas and debris to vent into the action. Same problem and same cause as using a silencer, just to a lesser degree, except that it pushes more through the gas tube and into the bolt instead of just dumping onto the mag and out the ejection port.

[K.L. Davis]

K.L.,
Would you please elaborate on this statement? I'd be much obliged to understand this better.

Well, at the risk of being one of those that vomit out a lot of gobeldy-goop(tm), the simple answer is that the rifle is designed to work with a specific internal bolt pressure -- this pressure is a function of the available pressure/volume of gas and the time it is available. With a carbine gas system on a 16" barrel, the internal bolt pressures run high... for the average slayer of paper plates and old bleach bottles, it is pretty much a none issue though.

Here (https://www.m4carbine.net/showthread.php?t=94) is a long and dry read, I really need to polish up when I get time.

[Aubrey]

K.L.,

Thanks so much. I posted a reply to your "After you pull the trigger" post.