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View Full Version : AR Bull Barrel, Fluted Barrel, etc.


GI Sandv
July 15, 2012, 12:52 PM
I'm trying to build an AR primarily for longer ranges. Although I will probably be doing a lot of plinking at the range as well, I want the rifle's primary capacity to be to shoot out to 500-600 meters with relative ease--practice, of course, being a significant consideration.

I've settled on a 20" barrel (although another thread persuaded me to consider an 18" as well) with a 1:8 twist. Although hunting is not this rifle's primary purpose, I may use it for smaller deer and other smaller game. I plan to buy/load some heavier rounds for this purpose (if I ever actually go hunting with it) and for any shots out past 300 meters or so. In my initial search, I found two barrels which seem to fit the bill. They're both stainless, 20", 1:8, and start with a bull blank and are then ground down to be fluted, providing a combination of less fluctuation, better cooling, and reduced weight. One of them is fluted the full length of the barrel, while the other is fluted only to the gas block, then runs the rest of the barrel at a more standard sized diameter. The two barrels are here:

http://intlmidway.com/intl/eproductpage.exe/showproduct?SaleItemID=577053 partially fluted.

http://shopwilsoncombat.com/Wilson-Combat-Match-Grade-Barrel-223-Wylde-Super-Sniper-20-1-8-Twist-Stainless-Fluted/productinfo/TR-SSBBL/

What difference does the full length vs. to the gas block only fluting make with regards to accuracy, cooling, barrel warp, etc?

I know Wilson has a good reputation generally, although I don't know about their reputation with these types of barrels. I know nothing of Stoner as a brand. White Oak is always on the list, as well as Noveske, and a smattering of other manufacturers as well. I don't know how big of a difference exists between a $400+ White Oak barrel and a $300 Wilson Combat barrel with similar specs. Any reason I should be wary of a Wilson Combat or Stoner barrel in these specs (or the 18" potentially)?

One final consideration: although I would like this to be a primarily long-range rifle, I will likely be putting plenty of cheap, surplus 55gr rounds through this at the local range when I can't get out to somewhere with more than a 200 meter capacity. I don't know of any reason why this would be a problem, other than the additional weight of longer range equipment. I'm fine with that aspect for this rifle. At some point, 2-3 years minimum, I may start building additional rifles to suit a variety of purposes. But that will have to wait and, until then, this rifle will be pulling double duty.

Thanks for the thoughts and comments

Creeper
July 15, 2012, 03:20 PM
If you're going to be shooting heavy, or perhaps VLD bullets at those longer ranges, the 1:8 might be borderline... may want to consider a 1:7.

I have no experience with the brands you've listed... using mostly Krieger and Satern barrels.

Fluting aids in heat dissipation because as material is removed the barrel surface is closer to the bore. When the bore gets hot the heat generated reaches the surface of the flutes faster than a plain barrel of the same diameter.

A plain barrel is a stiffer than a fluted barrel of the same outside diameter; however, a fluted barrel is stiffer than a regular barrel of the same weight.

The last 2 comments are paraphrased from a mechanical engineering paper done about 8 years ago on potential fluting benefits: Stiffness, weight reduction and heat dissipation.

That's all I got. Cheers,
C

tobnpr
July 15, 2012, 03:57 PM
Longer barrel= greater muzzle velocity.
7 twist is best, 8 twist might work...

Fluting is just another way to waste your $$ unless you need to make weight...
Read the section on barrel fluting, here.

http://www.6mmbr.com/barrelfaq.html#24650

Eghad
July 15, 2012, 04:15 PM
What bullet weights are you going to be using? You might try Black Rain or J&T Distributing makes some bull barrels with fluting

http://blackrainordnance.com/barrels.php

http://jtdistributing.net/store/page121.html

Creeper
July 15, 2012, 04:20 PM
Eghad... curious, have you tried a Black Rain barrel? I've used their uppers and lowers, but never their barrels.

Cheers,
C

Eghad
July 15, 2012, 04:41 PM
Not yet. I have yet to meet a dissatisfied user though. I didn't use get one on my last project due having to wait to get it.

GI Sandv
July 15, 2012, 04:43 PM
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GI Sandv
July 15, 2012, 04:45 PM
Creeper, tobnpr, Eghad,

Thanks for the links. The 6mmbr is especially helpful. I wasn't aware that you can bead blast a barrel for a similar effect. I assume this can be done after the fact if you end up with a non-blasted barrel to begin with?

The fluted barrel is a bit of a compromise. If this rifle were going to sit on the bench and never leave, I would stick with just a plain bull barrel. OTOH, because I want to be able to take it out into the woods from time to time, I figured that a fluted barrel would make this a less troublesome proposition. I assumed (or hoped, perhaps) that the fluting wouldn't too severely diminish the benefit of having a bull barrel.

As to the 1:7 or 1:8 twist, I settled on the 1:8 awhile back because I had read quite a bit of information that said 55grain rounds will pull themselves apart with higher twist rates, for which reason I believe the standard mil-spec M4s are 1:12. I would be relying on 55grain mostly for plinking at the range. But also, it's much cheaper so I could conceivably stock up on a good bit more of it for SHTF purposes. I think the 1:7 is too much twist for these rounds in 18-20" barrels, while 1:8 is barely acceptable. But, 1:8 still provides enough twist out of the 18-20" barrels to stabilize heavier rounds. So, it's a bit of a compromise. Anyone know any differently?

Regarding bullet weights, the short answer is I will be shooting the heaviest bullet I can from this barrel. From what I've read, 77grain will do fine. I know there are some even heavier rounds out there, and I haven't read much about them. Anecdotal evidence is appreciated.

Also, thanks for the Black Rain and J&T links.

Eghad
July 15, 2012, 04:46 PM
If you are talking about accuracy I think you will find the 1:8 twist the most used.

Achilles11B
July 15, 2012, 09:12 PM
M4's utilize a 1:7 rate of twist. 1:8 will be fine for 55 gr ammo, but if you're going for accuracy, I recommend experimenting with different weights and manufacturers to see what the rifle likes.

GI Sandv
July 16, 2012, 11:56 AM
I should have done my homework better. For some reason I remember reading about 1:12 or 1:14 barrel twist rates some months ago. It was probably a standard AR in .223, not 5.56 or .223 Wylde?

Whatever the case, that makes me feel better about getting a 1:7. I skimmed really briefly some info on the new M855A1 NATO round. 62gr with enhanced performance. Anyone know whether other non-military rounds in this weight perform decently in a 1:7 barrel? My biggest concern is that I had read that too much twist will tear a round apart as it flies, obviously affecting accuracy and penetration. I'll have to go back and look for those articles again.

Creeper
July 16, 2012, 12:27 PM
My biggest concern is that I had read that too much twist will tear a round apart as it flies, obviously affecting accuracy and penetration.

Some thin jacketed, varmint/benchrest bullets might come apart (J4 jackets, like those that Berger uses seem to hold up pretty well in twists faster than intended)... I've seen that happen, but I believe the current MK262 Mod 1 with the 77 grain Sierra Match King bullet (AKA Black Hills 77 gr. OTM) shoots great from a 1:7 twist.

Cheers,
C

Achilles11B
July 16, 2012, 10:27 PM
Perhaps experiment within the 68-77 grain range and see what the rifle likes.