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Old 05-01-2016, 06:48 PM   #1
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Pencil Barrel vs. Govt. Contour Barrel

In the event anybody is considering a build with an ultralight or "pencil" barrel, here is a photo showing a 16" pencil barrel with a 16" government contour barrel for comparison. Both are mid-length carbines, Palmetto on top and Spikes on the bottom.

It's hard to find a photo that compares the two, but I found this one when rooting through my photo files today. Hope it answers any questions y'all may have about the proportions of the two. FWIW

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Old 05-01-2016, 08:23 PM   #2
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Looks to save some weight. Thin wall thickness should be o.k. in a semi auto, but consistent auto fire might cause some issues. I like it. Thanks for the up close comparison.
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Old 05-02-2016, 01:55 PM   #3
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I could be wrong, but I believe the original M-16 that went to Viet Nam in 1965 had the pencil barrel contour, and like you say, it overheated bad enough for the government to switch to a heavier barrel contour.
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Old 05-02-2016, 06:20 PM   #4
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Hello,

Yes, the M16 and M16A1 had the lite contour barrel as did the early carbines.

There's all sorts of internet opinions on why the M16A2 barrel was only enlarged from the FSB (front sight base) forward and NOT under the handguards where it needs to be heavier to prevent barrel failures (sagging, warpage and blowouts) due to heavy, sustained, full-auto fire.

COLT Defense created the 14.5" SOCOM M4A1 Heavy Barrel (R0921HB) in 2003 to address the M4 barrel problems that's associated with heavy, sustained, full-auto fire.

Here's the M4A1 Heavy Barrel Specialized Armament: 02 Upper Receiver Group, Colt M4A1-SE

Here's a Standard M4 Barrel Specialized Armament: 01 Upper Receiver Group, Colt M4-SE

In case anyone is curious, COLT M16/M4 Barrels are rated for 12-15 Rounds Per Minute "Sustained Fire". Of course, you can easily exceed (double or triple) this rate of fire for a few minutes without worry because, COLT 4150 CMV (MIL-B-11595E) Barrels are Super-Strong!
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Old 05-08-2016, 04:10 PM   #5
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Here are 2 pictures of a Colt M16A1 "pencil" barrel circulation 1970-82 I'm guessing due to the raised C and Bell located on FSB. Diameter was .625 other than the chamber and behind front sight base/hand guard areas. When the A2 was adopted in 83 the barrel diameter increased to .750 dia. JayPee, your top picture is not a true pencil barrel but a step down from .750 to. 625 dia..



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Old 05-08-2016, 06:21 PM   #6
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Thanks for the correct information, Wags. I mistook it for a pencil barrel and apologize for the confusion. The top barrel in the photo is listed as an "ultralight" not a pencil barrel.

So if I understand this, in order for it to be a true pencil barrel the entire barrel would have to measure .625" diameter like the one in your photo, whereas the one shown only has the .625" diameter forward of the front sight base. i.e. an ultralight. The appearance would still be about the same forward of the front sight base, wouldn't it Wags?
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Old 05-09-2016, 06:02 AM   #7
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Quote:
Originally Posted by JayPee View Post
Thanks for the correct information, Wags. I mistook it for a pencil barrel and apologize for the confusion. The top barrel in the photo is listed as an "ultralight" not a pencil barrel.

So if I understand this, in order for it to be a true pencil barrel the entire barrel would have to measure .625" diameter like the one in your photo, whereas the one shown only has the .625" diameter forward of the front sight base. i.e. an ultralight. The appearance would still be about the same forward of the front sight base, wouldn't it Wags?
Correct JayPee. .625 barrel diameter other than at chamber and shoulder at front hand guard/FSB area would be considered a pencil barrel. The area forward of the FSB to flash hider threads is .620 I believe? A few barrel making manufactures still make retro style pencil barrels in 1-12, 1-9 and 1-7 twists for the retro head community. Majority of modern builders do prefer the heavier M4 style barrel like Bob pointed out with the step (cut out) forward of the front sight post if building a shorty carbine.

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Old 05-09-2016, 02:34 PM   #8
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Thank you sir.
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