Whats the advantage of an 18" barrel over a 14.5" Barrel?

[Averageman]

I have an older "Frankengun" with a 14.5 in. BCM upper. The lower has a Geissele trigger that sits in a Spikes lower. I've owned this over a decade, closer to 15 years and have around 2500 or more rounds through it. It was my first AR and to date I've had only one hiccup with it and that was due to a dirty chamber. I currently use an AimPoint PRO with it.
I've been thinking of buying another upper for it and putting a 3X9X30 Optic on the other upper and setting both aside to gift to my Son when he graduates.
I have to ask because I'm curious as to the the answers I would get from the brainbank here, other than as a platform for a more powerful , what would be the advantage?
I ask because I'm seeing a good deal on 18 inch uppers right now from Aero Precision.
Thanks
A/M

[ABNAK]

Increased effective range (terminal ballistics-wise) due to the longer barrel. Can't think of much else, not that it isn't a laudable goal. I'd say if that tripped your trigger then go 16" and call it a day.

[ExplorinInTheWoods]

So if you're going to put a 3-9 or any other higher magnification scope then the 18inch is the way to go. You gain or lose 30-50 fps for every inch of barrel with 223. You'll have a higher muzzle velocity so less drop at distance and usually 18 inch guns are rifle length so less recoil than a carbine or mid length. I have a noveske 18inch on my 3 gun rifle and love it. 18 is good for 3 gun or good for a coyote gun you'll carry around.

[BrigandTwoFour]

Advantages:

- Higher starting velocity
-- Less holdover/dial required for any given distance
-- More flexible point blank zeros
-- Increased fragmentation range
- Rifle length gas
-- Smoother recoil impulse
- Longer sight radius if using fixed irons

Disadvantages

- Increased weight, particularly at the front of the weapon
- 18" rifle gas, while mostly figured out, can be touchy with gas port size
- Increased length when dealing with tighter spaces

[longshot2000]

- 18" rifle gas, while mostly figured out, can be touchy with gas port size

This is very true, and not widely known. There are only a few barrels that handle 18" very well, and also, only a few that handle 14.5" and shorter very well. A Carbine gas system with a 14.5" Colt barrel works like a charm. A mid-length gas system with 16" is almost foolproof for most barrels. 10" rifle length the same. 18" and 10.3" are very, very tricky. Douglas does the best with 18" and Colt and LMT with the 10.3" to 12.5". Douglas figured out the 18" on the Mk12 barrel, and the barrel smiths I work with agree. Even more expensive barrel makers have extreme erosion at the gas port on 18" barrels.

That said, I am a fan of the long barrel for longer distances and accuracy. I am also a fan of the 14.5" M4 carbines. Just remember what each is designed for. Technical people will argue that accuracy is not a function of barrel length, and that is technically true over a short distance. The issue is not just velocity gets you out further, but for the 5.56 bullet, it is at what distance does the bullet cross the sound barrier, i.e., become transsonic. The faster it starts, the further out that place of turbulence is hit. The longer the barrel, the faster it start

[Hulkstr8]

So what's the range of optimal gp size for the 18"? Also, is it safe to say that a 14.5/16" is more of a "combat" length barrel?

[Jsp10477]

I’ve been told barrel steel plays a role with gas port erosion on an 18” rifle gas barrel. Frank at CLE will not use Krieger or Bartlein for 18” rg. He knows more than I do but KAC uses Krieger for their lpr’s. I “think” crane spec is .0995 for the gas port, I could be wrong. I have one with a .0993 (measured with pin gauges) that functions fine in Ga winters.

ETA: I’ve spoken with Frank over the phone to get the info about the barrel steels. If you’re placing an order he will take the time to explain.

[Averageman]

After reading all of his and contemplating what I'm getting in to a bit more, I will do one of two things.
Look for a 20 in barrel BCM upper, I have one and it rocks along all day long, or skip the whole thing and give him the carbine and twenty five mags and 1K of some 55 grain stuff I have in the closet.
Either way, it should be better than going in to a 18 in barrel I have no experience with.

[longshot2000]

I’ve been told barrel steel plays a role with gas port erosion on an 18” rifle gas barrel. Frank at CLE will not use Krieger or Bartlein for 18” rg. He knows more than I do but KAC uses Krieger for their lpr’s. I “think” crane spec is .0995 for the gas port, I could be wrong. I have one with a .0993 (measured with pin gauges) that functions fine in Ga winters.

ETA: I’ve spoken with Frank over the phone to get the info about the barrel steels. If you’re placing an order he will take the time to explain.

Exactly. I was reading your post, thinking I wrote it. Yes, Frank is the expert, and the source of my comment on the Douglas barrels in 18"

[Pappabear]

All is a an acceptable plan, but look what into BCM uppers. They small price crease is worth every penny. Your son will thank you endlessly.

PB