Accuracy from an AR15 “pencil” barrel when hot?


June 4, 2011, 03:17 AM
Once an AR15 "pencil" barrel gets hot (say fire a mag or two through it) How much does the group size open up at 100 yards?

I'm considering getting one for the lightness, I understand it's a trade off and I'd be willing to sacrifice some accuracy, just not too much.


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June 4, 2011, 05:51 AM
3 moa +/-

Friendly, Don't Fire!
June 4, 2011, 06:23 AM
I would think every barrel is different in how much accuracy would be lost due to heat. For some identical barrels, there may be no loss in accuracy and in others there may be more loss!

June 4, 2011, 08:24 AM
What brand and type are you considering, and are you planning to free float it?

A higher quality barrel free floated is going to stay more accurate than a cheaper barrel with standard handguards.

June 4, 2011, 08:40 AM
Hot or cold...the biggest no-no on a pencil barrel is sling tension.....with NO sling tension you should be fine...start torquing down on it and it's shotgun city...

June 4, 2011, 08:43 AM
It depends on several factors:

1. Type of barrel: mil-spec vs. match grade barrel
2. Presence of mil-spec front sight assembly and standard handguards
3. What do you call "hot"? 5 rounds in 5 seconds, or 500rds in 5 minutes.

I have a Bushmaster reciever with 16.5" "light" barrel. It measures 0.675" at the gas port. Before I replaced the factory handguard and removed the front sight assembly, it was around 3" at 100yds with good mil-spec ammo and/or commercial 55gr Soft Point ammo.

After replacing the upper reciever with a DPMS "Hi-Pro" reciever and gas block with a Yankee Hill Machine picitinny gas block and a Hogue free float handguard, I'm now getting 0.5-0.7" groups with "varmint" grade ammo and 1.5" groups with mil-spec FMJ ammo. It doesn't shift with heat up, and I don't run my guns till the barrel droops....... Mine is a "plinker" and varmint-hunting rifle that stays in a hidden corner in case an old "customer" comes for an un-welcomed visit. (retired law-enforcement officer...).

June 4, 2011, 11:40 AM
My Colt 16 inch, lightweight, non-floated barrel will easily break 4 inch clays @100 yds with a hot barrel...


Chris Rhines
June 4, 2011, 12:16 PM
Depends on the barrel. With a typical 2MOA lightweight barrel, 30-60 rounds over the course of a minute might open your groups up to 4MOA. Probably not much more than that.


June 4, 2011, 12:23 PM
im in the market now for a fluted barrel for my dpms carbine for the same reason. i can put 40 through it and still be minute of can at 100 yds.

June 7, 2011, 11:13 PM
Thank you guys for the input, I’m thinking about a Del-ton lightweight midlength.

June 8, 2011, 12:14 AM
There really isn't much difference between an M4 profile barrel and a lightweight barrel. Just the diameter from the gas block forward. When I went from an M4 profile to a lightweight profile, I didn't see any difference in accuracy loss as the barrel got hot. Of course, I really didn't notice too much difference in the weight either. How much accuracy loss you will actually realize will depend a lot on the quality of the barrel.

Maybe apples and oranges, but I shot this 20 round group using a barrel similar to an M4 profile. It was the last group of the day and I used my last 20 rounds. The barrel was already hot when I started and shot as quickly as I could get back on target. It was shot at 100 yards. The target dot is 1" in diameter on a 1/2" grid. I'd say that heat didn't affect this barrel much at all.

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