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Lightweight barrels are a common topic here.  Lots of requests for recommendations, lots of advice against them because of decreased accuracy, and lots of rumors about the subject.

I went out and tested several of my lightweight rifles for accuracy, and I ask that others do the same and post their results.  For this discussion, lightweight refers to a barrel that is thinner than a government profile or an M4 barrel, particularly in front of the gas block.  I would think 0.625 and 0.750 gas blocks would be fine, as would "pencil" profiles and hybrid styles, and any barrel length.

For my evaluation, I will use 10 shot groups from a bench, using a SS 10X mildot scope in an ADM mount as shown below. The lower used for each upper has a fixed stock and an ACT trigger. Ammunition is commercially available Black Hills 52gr HPBT and Federal Gold Medal Match 69 gr.  Shots were fired at about a twenty second interval.  Each barrel got considerably warm.

http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/LW%20barrel%20test/P1030556_zps21ba5870.jpg

Why ten shots and not three or five?  Please read this:  click

Groups will be evaluated using the On Target software available for free online and both Extreme Spread (CTC, center to center) and Mean Radius (ATC, average to center) will be provided.  For some reading on these ideas go here: click


The most important measure of the center is the mean radius.  It tells how all of the shots in the group compare to each other.  Extreme spread only gives the distance between the two farthest shots; it does not tell anything about the other shots in the group.  For example, a mean radius of 1" means that half of the shots fell within a circle with a 2" diameter.  Ammunition and a rifle that produces a mean radius of a little under 0.3" is considered match quality.


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1. First rifle is built up using a factory assembled BCM BHF hammer forged 16 inch 1/7 5.56 midlength pencil chrome lined barrel.  I have previously tested this barrel as can be seen here: click

http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/BCM16LWwACOG15_zps2cf32a71.jpg
http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/LW%20barrel%20test/2715LWtestBCM1652grand69gr_zpsadfbadc0.jpg


The first six rounds of the GMM went into that little cluster with one thrown right.  Then the range officer called "one minute" and I lost it in rushing the last four.

Note that the top group has a SMALLER extreme spread (labeled MAX, the straight line distance shown) than the bottom group, but a LARGER mean radius (labeled ATC, shown as the circle). Think about what that means.


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2. the second rifle is a home assembled RRA 16 inch midlength 1/9 5.56 barrel with chrome lining and a 1/9 twist.  This barrel is a bit thicker than a pencil barrel, measuring about 0.65 in front and behind the 0.75 gasblock.  I have previously tested this barrel here: click

http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/RRAMidFix_zps192dd0a6.jpg

http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/LW%20barrel%20test/2715LWtestRRA1652grand69gr_zpsc12c5819.jpg

First group went really well.  But the GMM was a fight.  I couldn't seem to get the rifle settled and was dealing with some glare off the front sight ears.  It is what it is.  


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3. The third rifle is a home assembled Daniel Defense 14.5 inch midlength 1/7 5.56 barrel with chrome lining and a pinned C2 Phantom flash hider.

http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/P1030572_zps128d1e6f.jpg


http://i1011.photobucket.com/albums/af236/onehalfmvsquared/hobby/LW%20barrel%20test/2715LWtestDD14552grand69gr_zpse83caebc.jpg


On the top group, I forgot that I had a FMJ hand-charged round first out of the mag and I put it on the target instead of the dirt.  It was not included in the group.

I was surprised at how low the 69 grain shot compared to the 52 grain.  On the two 16" rifles, the heavier load was about an inch and a half low.  The 14.5" barrel shot them 3 inches low, almost off the paper.  I did not expect to lose that much velocity with 1.5" of barrel.

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Conclusions:  All rifles have standard hand guards, are not free floated, and all rifles shot well within my personal defensive standard for accuracy:  A Mean Radius of 0.8" or less and an Extreme Spread of 2.5" or less.  This standard implies that at 500 yards, half of the shots will fall within a 8-inch diameter circle, with none exceeding 13 inches.  The width of my torso is 13" and I've got a medium athletic build.  

I cannot imagine a scenario short of TEOTWAWKI that would require me to make a rifle shot at a distance greater than 100 yards.

A lightweight barrel of good quality with standard hand guards is just fine for a defensive long gun.

and as a homage, here's Molon's test of a Colt LW barrel click