Thursday, July 27, 2017

Interesting Test Of Pencil Barrels


The original M16/AR-15 from Colt was produced with a pencil barrel. Later iterations of the rifle and carbine had a heavier and thicker barrel because it was found that the pencil barrel would flex when it got hot. The barrel flexing resulted in a change in the point of impact. The practical effect of this barrel flexing for the military was that shots ostensibly on target were missing the enemy at longer ranges.

You can see the difference in thickness between a pencil barrel and a "government" profile barrel in the pictures below. Both of these barrels (and the pictures of them) are from Faxon Firearms.

Faxon 16" pencil barrel

Faxon 16" M4 government profile barrel

Ian and Karl at InRange TV are doing a series called "What Would Stoner Do". The latest in their WWSD series tests the effect that heat can have on pencil barrels and the point of impact. They tested both a modern Faxon barrel and an original Colt SP1 barrel. Faxon claims that their proprietary method of building in stress reliefs mitigates the significant change in point of impact caused by heat. Part of Ian and Karl's reasoning behind testing pencil barrels is that a pencil barrel is a quick way to reduce the weight of the rifle.




I found this highly interesting as I am in the process of assembling parts to make a lightweight AR using this same Faxon pencil barrel. I got a great deal on one at the recent NRA Annual Meeting and decided that I "needed" another AR. I am also in the process of putting together a retro styled clone of the M16A1 using a mix of original and modern parts. This latter rifle uses a 20" barrel from Green Mountain Rifle Barrels which has the original 1 in 12" twist. My dad qualified Expert with such a rifle back in the 1960s and the build is partly meant to honor him.

6 comments:

  1. I understand that the 1:12 twist rate is accurate historically for old school m16. But why do this? You will probably suffer in stability in anything larger/longer than 55g m193. There are a ton of great, better BC projectiles in the >55g'ers, eg sierra matchkings >= 69g.

    Ian [I love all of Ian's vids/projects] rightly points out that the pencil barrel aspect makes little difference in modern barrels but remember the freefloat barrel aspect of your historical project is dashed and accordingly the shooting stance/rest makes a ton of difference.

    Keep on truckin' in your support of 2a, Mr. Richardson. You make a difference.

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    1. I used the 20" 1:12 twist barrel (or will ) in my retro M16A1 because it is historically accurate. That build is using as many old parts that are still available as possible. The upper (Colt), the pistol grip, the A1 stock, the flat delta ring, and front sight post are all original parts. The barrel, the bird cage flash suppressor, the lower, and the "innerds" are new. I know I'm limited to the 55 grain M193.

      My modern build with the Faxon pencil barrel will be free floated with an ALG handguard.

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  2. Nice. I get your intent.

    We have a regular who shoots a 70's Colt carry handle full length AR in our East TN 3gun matches using irons only. He does very well. You will be pleased.

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    1. Cool! Where in East TN are these 3-gun matches?

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  3. What would Stoner do? I'm assuming have lunch in an outhouse.

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