16" pencil barrel

AR/M4 AR Technical Discussion
1

I’m pondering converting over an upper to a pencil barrel. This upper normally has an Aimpoint and BUIS, and I got to wondering why am I lugging this extra weight around if I’m not using magnified optics? The red dot will be cover at least 4" at 200, so whats the use of the medium contour barrel if I’m not going to take advantage of it?

So I guess I’m asking if I’m thinking straight? And does anyone one see any real disadvantage to running a pencil profile when your main optic is a red dot (yes, I know they heat up and tend to get less accurate with sustained fire)?

2

The way I see it, the only real advantage to a pencil barrel (lightweight barrel) is weight savings. If this is going to be a range/HD AR, I see no reason why you should not change out to a pencil barrel. Lightweight barrels can still be fairly accurate out to around 300-400 yards. If this is going to be used hard and a large amount of sustained fire, I would advise against changing the barrel out. As far as the red-dot, regardless of the barrel you decide to use, they are very useful out to 200 yards. Any further than that, I recommend using a magnifier or a magnified optic (1-4x24 or 1-6x24).

3

Yes it’ mostly my range, fun gun, with the occasional three gun trip when I’m feeling feisty. And thanks for verifying my point, my sights are really good out to 200, but it gets tough to make hits much past 250. Just seems like I’m carrying weight I don’t need. I could just switch over to a scope, but I would really like to try going lighter.

4

Non sequitur.

Range Report: Precision Shooting With an Aimpoint

First and foremost, the Aimpoint red dot sight is a combat sight. Its primary purpose is for use in situations that require “reflexive shooting” at multiple targets, at close ranges. The Aimpoint excels in this type of shooting because it easily allows you to shoot with both eyes open and to focus on the target while shooting. All of my self-defense AR-15s have Aimpoints mounted on them. However, should the need arise (for example, making a head-shot on an aggressor at 100 yards who has most of his body behind hard cover) the Aimpoint sight is certainly up to the task of making precision shots.

There are those who claim that when using an Aimpoint sight with a four minute of angle dot, that it is not possible to shoot groups that are smaller than four minutes of angle in extreme spread. One such person has gone so far as to claim that groups shot from 100 yards using an Aimpoint with a 4 MOA dot will be “greater than 4 inches. Usually much greater.” As we shall soon see, such statements are completely false.

To determine the level of precision obtainable when using an Aimpoint sight with a 4 MOA dot, I mounted an Aimpoint ML2 with a 4 MOA dot on one of my Krieger barreled AR-15s. This AR-15 is easily capable of producing consistent sub-MOA 10-shot groups at 100 yards when using a high magnification scope. Shooting with the Aimpoint sight was done from a bench-rest at a distance of 100 yards using NRA 200 yard High Power type targets scaled-down for 100 yards. (The aiming black is approximately the same width as a human head.) Sighting was done using the whole dot centered on the bullseye. Three 10-shot groups were fired in a row for evaluation.

Zeroing the Aimpoint sight at 100 yards was conducted during a down-pour with 20-25 mph winds. The first two 10-shot groups were also fired under these conditions. The first 10-shot group had an extreme spread of 1.41”.

With another couple clicks of windage and elevation adjustment, the second 10-shot group had all shots going into the X-ring. The extreme spread for this group was 1.19”.

Just as quickly as the down-pour had started, the rain stopped, the winds died down and the sun began shining again. I posted a new and dry target on the 100 yard backer and continued shooting. The third 10-shot group had an extreme spread of 1.14”. The average extreme spread for all three of the 10-shot groups was 1.25”.

ETA

Here’s a little demonstration of the “practical accuracy” obtainable when using an Aimpoint with a 4 MOA dot. For this exercise, I used a 14.5” chrome lined, NATO chambered carbine. Shooting was done from the prone supported position. From a distance of 50 yards, I fired ten quick shots at an FBI “Q” target. The results . . . ten “bullets in the brain pan, squish!”

The 10-shot group has an extreme spread of 1.18”, which at 50 yards is equivalent to 2.26 MOA; far smaller than the 4 MOA dot on the Aimpoint. Again, this disproves the spouted nonsense that “practical accuracy” is not possible when using an Aimpoint with a 4 MOA dot.

Remember, I have astigmatisms in both eyes, which make using an Aimpoint a bit of a challenge. I have no doubt, that someone with better eyesight could produce better results.

…

5

IIRC, the front sight post on standard A2 irons subtends 11MOA on a rifle.

If I can’t more than easily beat 11 moa with decent ammo from an AR rifle from a bench, it’s a damn bad day.

6

Thanks for that, I’m pretty certain I have read that before but it was good to read it again. While I know it is possible to shoot groups like that, at much past 200 or 250, the challenge for me most of the time is just making out the target at that distance, anything under less than ideal lighting becomes a challenge when using non-magnified optics. Trying to hit a 6" plate painted white at 200 with a 4" dot is tough, I don’t care who you are, LOL. But I tend to limit myself to what I know I can hit anyway.

7

You haven’t said what your old barrel weighs, so it’s hard to offer an objective opinion.

With a light, floated barrel, your first shots tend to be pretty good, with the groups opening up as the barrel heats up. I prefer a light rifle for most things.

8

I have no idea, but I would say its a medium heavy profile, it does not reduce down under the rail, gas block to chamber is pretty much the same diameter.

9

What is the diameter difference between a pencil and lightweight barrel?
I always thought they were synonyms of each other.
What are the criteria for being considered a pencil vs lightweight profile?

10

For decades they meant the same thing; the Colt 16" barrel found on the Colt 6520 defined the light-weight profile for carbine barrels (and of course the original M16 barrel did for rifle barrels.)

In recent years, new manufacturers have been making-up their own profiles and calling them a light-wight barrel. For example, Centurion calls their barrel pictured below a light-weight barrel even though the profile and weight are clearly different than that of the Colt 6520 barrel.

A few data points . . .

Colt 6520: 1 pound, 6 ounces.

Centurion Arms 16” “light weight”: 1 pound, 10 ounces.

Colt 6920: 1 pound, 12 ounces.

Noveske 16” N4: 1 pound, 12 ounces.

Colt 6721, 16" HBAR: 2 pounds, 3.4 ounces.

….

11

Thanks Molon.
Random observation, I was a bit surprised to see how short the gas system is on some of those barrels, given their length.

12

A true “lightweight” or “pencil” barrel tapers from .67" to .60" behind the gas block, is .625" at the gas block, and is .57" in front of the gas block with a small flare before the gas block and before the muzzle threads. Anything smaller than a .75" or “Govt” barrel could be called lightweight though.

13

http://www.brownells.com/rifle-parts/barrel-parts/rifle-barrels/ar-15-m16-16-5-56-barrel-assembly-prod71164.aspx

16" lightweight Colt barrel assembly in-stock in case you go through with your plan (which I think is a good one). Will need the crush washer and FH as they’re not included.

14

Thanks, but thinking of going middy too. My last few have been Melonite as well.

15

I am a fan of A1ish inspired profiles on carbines for some. The OP’s rifle could very well be one of those. For 16" barrels, I would definitely look at a longer than carbine gas system, something in the range of mid to KAC length.

16

Ha! I don’t know what religion my barrels are. Perhaps they are atheist.

17

Na, just a simple life.

18

Good to know. Not to take the thread off topic, but does anyone know what barrel thicknesses would be considered pencil/lightweight/midweight for a .308/7.62 AR?

19

LOL, damn spell check.

20

FWIW, the M14 barrel tapers from .74" to .63" before the gas cylinder and then is .60" in front of the gas cylinder. So really, not much thicker than an M16A1 barrel. There probably aren’t many 7.62 AR barrels that are that light though. The MK17 SCAR has a pretty light profile but I don’t know the dimensions.