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Accuracy in a 18" pencil barrel good enough?


2Xalpha

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Hi,

I want to build a lightweight competition AR, and think about saving some weight going with a lighter barrel. In general I was recommended the BCM 18" as a good value/ quality option (2.5 lbs/ 1133 grams, http://www.bravocompanyusa.com/BCM-18-SPR-SS410-Barrel-with-Rifle-Length-Gas-p/bcm-brl-rec-18ss.htm),but I wonder if I should go with a lighter profile instead.

Some other options I've seen:

- CMMG 18" (weight?): https://www.cmmginc.com/shop/barrel-sub-assm-18-0-mt-416ss-5-56mm/

- Noveske 18" Lightweight Contour, 2 lbs/ 907 grams: http://www.shopnoveske.com/products/lightweight-5-56mm-stainless-barrel
- JP Light Contour, 1.94 lbs/ 878 grams: http://www.jprifles.com/buy.php?item=JPSM223-18L8

Is it dumb to skimp on the weight? Anybody have some comparable data on how much impact might change (I say might, because I guess it will depend on the quality of the barrel)? Will the difference in accuracy be noticeable, especially for the requirements we have in IPSC/ 3 Gun (I guess not)? Again, does anyone have some data? :)

Please recommend some other good value barrels for the build, and comment the ones I've mentioned. The requirements are an 18" barrel with rifle length gas tube, preferably with a good quality/ price ratio.

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Match barrels will do what they were made to do. What is good enough to you may not be what others' consider good. I expect my barrels to be well within sub MOA as I don't want to second guess my equipment. Buy once and regret never.

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So you are suggesting for instance a light contour JP barrel? JP barrels have a very good reputation, but they are a bit expensive. The CMMG barrel was cheap, but the quality probably suffers..

Other good light profile alternatives?

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Thanks, found this one from Faxon Firearms: http://www.faxonfirearms.com/p/98/18-556-ar-15-4150-black-qpq-govtsocom-rifle-gas

18", rifle gas, 1.95 lbs/ 885 grams. Look really cheap at MSRP $179, but how is the quality?

ISO:9008 Certified, AS:9100 pending, TS Certified.

He're our guarantee: if you have an issue, we fix it or make it right.

Its that simple.

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Thanks, found this one from Faxon Firearms: http://www.faxonfirearms.com/p/98/18-556-ar-15-4150-black-qpq-govtsocom-rifle-gas

18", rifle gas, 1.95 lbs/ 885 grams. Look really cheap at MSRP $179, but how is the quality?

ISO:9008 Certified, AS:9100 pending, TS Certified.

He're our guarantee: if you have an issue, we fix it or make it right.

Its that simple.

Forgot to add our "light" barrels are nearing final assembly. Its gov't behind the gas block, .625" gas block, and pencil from there forward. I estimate about 1.75 lbs with our normal accuracy.

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OK, I think I've found that the accuracy in the lighter barrels typically will be good enough.


The next question is balance. While I want a light rifle, I still want it to balance well. How can I determine the balance with the different parts?


Parts list:

- Regular mil-spec upper/ lower

- ACE ARFX rifle length stock

- Handguard choice: Leaning towards AP Custom 15" Ultra Light handguard at 6.2 oz/ 175 grams (http://apcustomusa.com/product/gen-ii-ultra-light-series-carbon-fiber-handguard/)

Also consider:

- JP 15.5" MK III Modular Hand Guard (JPHG3-6M-RC) at 15.2 oz/ 430 grams (http://www.jprifles.com/buy.php?item=JPHG3-6M-RC), or

- JP 15.5" MK III Modular Hand Guard (JPHG3-6M) 18.3 oz/ 519 grams (http://www.jprifles.com/buy.php?item=JPHG3-6M)

(weight difference between AP and the lightest JP is 9 oz/ 255 grams)

- SJC Titan comp


Some barrel examples:

- JP 18" light contour 31 oz/ 878 grams (http://www.jprifles.com/buy.php?item=JPSM223-18L8)


(weight difference between BCM and JP barrel is 9 oz/ 255 g)


Looking at their location, the different handguards and barrel profiles will approximately have the same impact on the balance.

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I think that if you compare the weights you will find that the BCM barrel is on the heavy side of things and you don't hear about that many people running them. I also have no idea whose blanks they use and that's what really matters. We are fortunate in that we have lots of good choices out there and the manufacturers are willing to stand behind their products. I am certain that if you have issues with a Nordic, Faxon or any of the Ranier arms barrels they will help you out. I am also certain that these companies have done enough testing to know what works and what does not within limits. The "unknown" out there is not as much if the barrels are going to shoot well, its more along the lines of durability and life as far as I am concerned.

Years of shooting NRA HP and LR has provided me with lots of barrel information, this is not to say that things are not changing for the better but NRA HP and LR demands more in terms of accuracy and provides the shooter with better target feedback then 3G ever will.

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"It's the archer, not the arrow". :D I think we can agree that, shooting as much offhand as we do in IPSC & 3 Gun, shooter error often will be way more determinantal than the mechanical precision. However it's good to know in the back of your mind that you have a minimum level of accuracy to fall back on when engaging those long range targets. What should one expect, 1 MOA, 2 MOA? And how does that change as the skinny barrel starts to heat up?

The "unknown" out there is not as much if the barrels are going to shoot well, its more along the lines of durability and life as far as I am concerned.

Probably it sounds like I'm a little hung up on accuracy, but as you mention it's actually more important how many thousands of rounds the barrel will hold its level of precision. I think different steel quality (CrMo 4150, vs. 4140 vs. 416) and treatments (chrome lining, nitriding or cold hammer forged) comes into play.
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There was youtube video posted recently that had a review of the faxon pencil barrel, appears the reviewer was able to get a .75" Group to start, dumped a mag and then reshot a 1.75" Group. Appeared to be 100yds with Fed Gold Metal Match ammo.

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JP light contour paired with ARFX stock for me. I love it!

I'm definitely sub-MOA at 300 with 77gr. Theoretically, the heavy barrels will maintain accuracy better after the barrel heats up. I'm no precision shooter, but I can't tell any problems with long range accuracy at the end of a 30 round stage.

Edit: using the Seekins 15" flat bottom handguard

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Thanks, found this one from Faxon Firearms: http://www.faxonfirearms.com/p/98/18-556-ar-15-4150-black-qpq-govtsocom-rifle-gas

18", rifle gas, 1.95 lbs/ 885 grams. Look really cheap at MSRP $179, but how is the quality?

ISO:9008 Certified, AS:9100 pending, TS Certified.

He're our guarantee: if you have an issue, we fix it or make it right.

Its that simple.

Forgot to add our "light" barrels are nearing final assembly. Its gov't behind the gas block, .625" gas block, and pencil from there forward. I estimate about 1.75 lbs with our normal accuracy.

keep us in the loop when the "light" barrels will be available....hopefully 18" with rifle gas?

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Typically people say thinner barrels will have more dispersion as they heat up, but data seems hard to find. Faxon, do you have any data on heat dispersion with the 18" 5.56 Gov't/Socom Rifle Gas barrel? (http://www.faxonfirearms.com/p/98/18-556-ar-15-4150-black-qpq-govtsocom-rifle-gas) If you were to guestimate, how much will the heat dispersion be different from for instance one of your 18" heavy barrels: http://www.faxonfirearms.com/p/106/18-556-ar-15-416-r-stainless-matte-heavy-fluted-mid-gas

Mrgunsngear did a short test with one of your 16" pencil barrels where the group seemed to open up from about .75 to 1.25" at 100 yards after a 30 round mag dump, I would love to see more tests like this.

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While I can appreciate the work someone does uploading a video, Mrgunsngear's test does not really tell us that much. We do not know if the gun will regularly put out 3/4" groups when cold. The 1.75" 3 shot group could be well within normal cold groups. A ten shot group or multiple 5 shot groups would have been more statistically significant. I do agree that a lightweight is fine, and I own a 18" lightweight from JP. I have no complaints from it.

I know it is from ar15.com, which some people don't like, but it is still a valid post.http://www.ar15.com/forums/t_3_118/279218_The_Trouble_With_3_Shot_Groups.html

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Seems like there are many myths and little scientific data on light vs. heavy barrel accuracy. Some say skinnier barrels have come a long way, perhaps outperforming some old heavy barrels, but where's the data?


Heavier barrels will typically be less affected by heat, but in theory a lightweight barrel that's concentric and stress relieved should be almost just as good. Thats the theory, but then there's always the real world. And of course you can get shitty heavy barrels too.


When testing accuracy, groups opening up could just as well be the shooter getting tired and losing concentration, anticipating shots, etc., which can happen to even good shooters. To remove as many human factors as possible, a test should be conducted with a rifle bolted onto a machine rest, like mentioned in the ar15.com post. Then we would be able to see some example of differences in the mechanical precision.


Then set up a camera by the paper target to see where the rounds go, and measure the group afterwards.

- First 10 shots fired with with 1 minute intervals to let the barrel cool down in between

- Then start blasting 50-100 rounds with just seconds in between to get the barrel warm


Compare some different barrels, and that would give us some scientific data. Even if renowed manufacturers might have some good and less good barrels within each batch, I think we would be starting to see a trend.

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This is a pretty good discussion reference rifle barrels. If your looking for data, look on any competition rifle firing line and you are going to find medium to heavy barrels on all the rifles. Those rifles are getting plenty hot shooting 25 or so rounds in 12-15 min in magnum calibers.

Finding true quantitate data is always going to be hard as there are so many variables. I think a "good measure" is a 10 round cold barrel group and then after some more shooting, say 30 rounds, another 10 round group. While this will not tell you everything about your barrel accomplishing this test is within the realm of possibilities and a 10 round group is a pretty good picture of what your rifle system can do.

For what its worth i'm looking for a ten round 2" group at 200 yds for my 1000 yd long range rifles with low ES. I am confident that many people that claim their rifles will shoot 1/4 MOA all day long.... would not be able to deliver such performance on demand. For my 3 gun rifles, im slightly less picky and look for 2-3" at 200 yds and its there with 77's and about 5-6" with 55 short range ammo. Im also shooting with a 6x scope so this needs to be taken into consideration as a higher power scope might tighten things up slightly.

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I've spoken with JP, and they say that both the 18" light and medium contour will hold 1 moa (often less), with the medium being slightly more accurate. They don't have any data on difference in heat dispersion. They did however say that the balance of the rifle will be more important, with most shooting a slightly front heavy rifle better (steadier sights, I guess).


Sorry for all the nagging about dispersion on light vs. medium profile, but I think there might be a higher demand for precision in IPSC Rifle in Europe as opposed to 3 Gun in the USA. A common conception in Europe is that we often shoot long range at smaller paper targets, while in the U.S. larger steel targets are used. Paper targets don't provide any feedback, so you need to call your shots and trust your equipment. Many of the good IPSC shooters I've spoken with are proponents of somewhat heavier barrels, medium contour being the "minimum", but I want to challenge that by looking at data.


Lets take an example on what accuracy that's needed in IPSC Rifle: The A-zone of the IPSC Classic target (smaller than Metric) is 15cm (6") wide, the whole target is 45cm (18") wide. At 300 yards (275m) the 6" A-zone will be 2 moa, while the whole target (18" wide) is 6 moa. Assume only Alfa is good enough. Then move out to 350 yards (320m), probably will never encounter longer ranges than that in IPSC. At 350 yards the 6" A-zone will be 1.7 moa (if it was 7" it would be 2 moa at 350 yds).


While there seems to be no data on heat dispersion available, my impression is that different barrel contours will be negligible. (Would very much welcome data, though). It seems like the rifle's balance is more important, and now I'm just worried that the 18" light contour (shaving off 0.5 lbs/ 9 oz/ 250 grams compared to 18" medium contour) will be too light coupled together with the ultra light AP Custom handguard (also shaving off 250 grams compared to the 15.5" JPHG3-6M-RC handguard), thus moving the balance point a little too far back. Will be running a Swarovski 1-6 and ACE ARFX stock.


Of course the balance will be a lot of personal preference, I just want to hear what you guys think.

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Bear in mind that there's a lot more to barrel accuracy than profile, even taking the shooter out of the equation. How was the barrel rifled? What's the twist? What kind of a chamber does it have? How well is the bolt mated to the barrel? IMHO ammunition is at least as important as the gun itself.

Regarding the barrel heating up, I've been told (don't ask me to prove it) that there can be a benefit to a lighter barrel in that, yes, it will open quicker but for most stages it won't matter-- and the lighter profile allows it to cool quicker to full recovery between stages relative to a thicker barrel. Remember that a barrel's "heated accuracy" will only matter if the distance shot is at the end of the stage vs the start of it, again pointing too how often does it truly matter? It really depends on the match designs you shoot. If your matches are heavy on distance it could matter a lot. If your matches only have a few distance shots that can be taken at the start of the stage, it may not matter at all.

Personally, I opt to find the best quality and heaviest profiled barrel I can that will balance the gun to my taste. I don't care if the gun is heavy as long as it feels good in my hands. Build it and then test it. If it works to your satisfaction then awesome! If not, start saving the $$$ and try again. Ultimately there are too many variables in this game to figure it all out with certainty on paper alone. It has to be theorized as best as possible and then we must take the leap of faith into reality and put the plans to test in physical action. The worst part of it, of course, is that a "garage gunsmith" can build two apparently identical guns and they will likely group differently and one will prefer a different ammo than the other. That's just life.

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[quote name="2Xalpha" post="2381770" timestamp="1429887602

Of course the balance will be a lot of personal preference, I just want to hear what you guys think.

When planning, I try to figure the weight of the stock vs everything in front of the receiver, considering everything on or above the receiver to be neutral. That will give a decent approximation of balance. Remember also that if you're close to your ideal balance point, you can add or swap out various parts to get the balance more finely tuned. If you think your design will be too barrel light, you can possibly switch to a heavier muzzle device, which is an easy fix.

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Too much planning, not enough shooting. The only way to know if you will like a different set up is to actually try shooting it. There always seem to be a large number of unintended consequences to even small changes to a competitive rifle that need to be evaluated as a whole to determine if the change is a success.

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