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308 barrel 16" with 5R rifling


Gibbs

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Not many out there.  Have seen a few 5R rifles, and have a 6.8 SPC that I put together with an AR Performance 5R barrel, and wanted to see if I could find one in .308 for my new LR 308.  I actually started out looking for a mid length gas barrel as I really don't like the carbine length gas in the DPMS LR308 rifle I have.  So, I figured if I can look for a mid length gas system, why not look for one with 5R rifling as well.   Not a lot of choices out there.  Boots Obermeyer made the first 5R barrels some years back and he cuts barrels pretty deep with his barrel making machinery, rather than using button rifling.

 

What have you all heard for 5R barrels, 16" length mid length gas systems?  Ranier Arms has some, but they say  "Polygon" barrels and I am not well versed on that style.

 

 

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Those Rainier barrels you're speaking of are made by Black Hole weaponry, and are not Obermeyer 5R cut.  They are more like a rifling with 5 waves or bumps.  Look at their site (thier new site is almost worse than their last one) and google Polygonal rifling and you'll see http://en.wikipedia.org/wiki/Polygonal_rifling

 

Lothar Walther also makes polygonal barrels, but I think they are only 3R.  Those, I believe were the barrels used for the original LaRue OBRs before LaRue started making their own barrels.

 

For top quality, you can get a .308 5R cut barrel blank in the contour of your choice from Bartlien or Krieger and have a gunsmith chamber it for you in any gas length system you like.

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Brownell has a 16" barrel 5R rifling  416R SS here: http://www.brownells.com/rifle-parts/barrel-parts/rifle-barrels/308ar-barrels-prod69784.aspx?avs|Cartridge_1=CTT_308 Winchester  They are not 1:11 rifling, as I think those can be handloaded a bit better than 1:10 twist barrels.   Not promoiting any website, but that link shows info as to button riflled barrels, all ready for mounting into a receiver. Just wish it were 1: 11 twist rather than 1: 10.  I feel that the looser twist might open up with less pressure for handloading.  My recent batch with 150 gr Hornady are pretty good groups using IMR 8208 XBR powder and magnum primers.

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a "looser twist" would refer to something like 1 in 11 or 1 in 11.25, or even 1 in 12.  I remember reading one time, from a pretty knowledgeable barrel maker that the less twist it takes to stabilize a given bullet, the better.  1:11 is a bit "looser" than 1:10 and will still stabilize the 168 gr bullet very well.  It would stabilize 150 grain without any issues at all. 

 

By "loosening" up the twist, you can reduce pressures slightly, as they did this with the 6.8 SPC.  By going from 1:10 to 1:11 or even 1:11.25, this allowed for a bit hotter handloads.

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By "loosening" up the twist, you can reduce pressures slightly, as they did this with the 6.8 SPC. By going from 1:10 to 1:11 or even 1:11.25, this allowed for a bit hotter handloads.

I don't doubt what you're saying it true, but I think the quality of barrel makes a difference as well.

After having a long conversation with KK Jensen and Mike Dagerness (both from Jensen Precision, which is now Proof Research), they said near the exact opposite. They state, if you have a high quality barrel, a tighter twist will handle all the pressure you put through it. I have one of their carbon fiber wrapped barrels on my .308AR. I have a 17", rifle length gas, w/ 1:10 twist. They flat out told me, "shoot whatever you want through this barrel."

So far I've shot 145gr up to 175gr. From cheap steel surplus to high end match.

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  I think you will find that chamber /barrel pressure has little to to do with what twist rate the barrel is . Now what type or how many lands & groves , might ,but that is not something even most barrel makers have the ability to measure accurately .

 

The 1-10 ,IMO, shoots just about every thing , with good results , But that's your call , some swear by the slower twist rates , for long range with heavy bullets

 

I never owned any with other than 1-10 , so I can't compare the different twist rate barrels .

 

Obermeyer Approved 5-R™ Style Rifling Now Available!

(PLEASE completely read description below)

Thanks to approval by Boots Obermeyer, Krieger Barrels, Inc. is now offering the true Obermeyer 5-R™ rifling pattern as an option on limited calibers with our barrels.

At this time we are limiting the 5-R™ option to the calibers listed below, but may offer others in the future as greater demand arises.

PLEASE NOTE: We are not currently, and have no future plans to offer 5-R™ rifling in our finished 'Gas Gun' lines of M14, M1 Garand, AR-15, and AR-10 variants. Nor will we make a 5-R™ blank longer than 33" (32" finish length).

5-R™ rifling is ONLY available in standard bore/groove dimensions listed and standard twist rates (**) at this time. Please call if you have questions about availability of a certain caliber/twist combination.

There is a $30.00 up-charge to the base cost of the barrel for 5-R™ rifling.

Currently available bolt gun calibers with 5-R™ rifling:

6mm (.236" & .237" bore diameters, .243" groove)

 ** NO twist slower than 1-9 for 6mm 5-R™ barrels are available. Good authority has shown that short, light, 6mm bullets do not perform well in most 5-R™ barrels. We have no knowledge as to why, but do not want to risk an inaccurate Krieger Barrel being on the market.

6.5mm (.256" bore, .264" groove)

7mm (.277" bore, .284" groove)

.30T Palma (.298" bore & .3065", .3070" & .3075" groove diameters)

.308 cal (.300" bore, .308" groove)

.338 cal (.330" bore, .338" groove)

Description of 5-R™ rifling:

 

5R_Rifling_profile_for_website_half_size

Visual aid to describe our 5-R™ style of rifling. Some dimensions have been changed to allow a better understanding of the rifling style. *Sides of groove have a 'ramped' transition to the land.

Not to scale 

 4_Groove_Rifling_profile_for_website_hal 

 

Visual aid to describe our traditional 4 groove rifling. Some dimensions have been changed to allow a better understanding of the rifling style. *Sides of groove are nearly parallel. 

Not to scale

 

 

The Obermeyer 5-R™ style rifling is simply a different style of rifling that has a more 'ramped', or angled transition from the groove to the land and back down from the land to the next groove. Our conventional 4 groove rifling has nearly parallel sides to the groove. The internet is full of information describing perceived benefits to the 5-R™ rifling over conventional styles, but most of this is comparing "apples to oranges" as they are usually comparing one manufacturer's "non 5-R™" to a different manufacturer's "5-R™" barrels. We have honestly seen no significant differences in accuracy or performance between the two styles of rifling when comparing our barrels.

 

Thank you, Krieger Barrels

 

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post-15036-0-36205000-1408124584_thumb.jBoots Obermeyer may have a different opinion on 5R vs others as being bull, but he is pretty much the one that invented it many years ago.  Several of the major barrel makers learned from Barrett Obermeyer on their practices.  I agree it is all different and all subjective to one's opinion.  This link:  http://www.stockysstocks.com/servlet/the-666/Rock-Creek-5R-Cut/Detail  gives a very good account of benefits of 5R barrel and there are probably others as well as there are others that stick with simple 4 or 6 groove patterns for their rifling. 

 

1:10 twist will handle every bullet out there that you might want to shoot form an AR-10.  Some might say they work their best on the 165 and 168 match bullets with boat-tails the best.  What I have been told is that the heavier bullets need a bit faster twist to stabilize them well.  In the 6.8 SPC they found that 1 in 13 twist would work on 90gr, 100gr and 110gr, but when you loaded in the 120 grain it was not enough twist to give the bullet performance that the bullet was capable of doing.  In 6.8 SPC the 1:9 was ok, but was not able to handle the higher pressured SSA ammo as well, and some of it was due to the fact that the chamber was not set up as as SPC2 chamber.  IE  there was only 0.050" freebore on the original SAAMI specs of 6.8 SPC where most of the newer barrels and makers are using chambers with 0.100" freebore  with the relaxed twist of around 1:11 and some out there of 1:12.  In handloading you would see pressure signs with less powder in the tighter SPC1 chambers over the SPC2 chambers with the longer freebore.  Kind of like the 5.56 NATO would be with it's longer freebore for hotter military rounds as opposed to the .223 Remington ammo.  You could shoot 5.56 x 45 ammo out of a barrel just made for .223, but you could not (should not) do it very much as there are higher pressures.

 

Gas systems have an effect on chamber pressures as well, since the hole for releasing the gas to move the bolt carrier is closer to the bore, they pressure at that point is higher than that of mid length or rifle gas systems.  Further down the barrel those latter gas systems also take a little larger port hole for the gas block since there is less available pressure/gas at that point for bolt carrier movement.

 

Taking these things into account, there are very nice .308 rifles out there in the AR platform that do exceptionally well with 1:10 twist and 4 or 6 groove rifling.  They are, after all, somewhat designed for battle rifle conditions and as such if you look for extreme accuracy, you are better at looking at bolt action .308 over the gas operated semi autos like the AR series.

 

The barrel I have is not really bad at all.  I have been able to get a group at 100 yard of 0.366" using 150 gr Hornady SP bullets non BT with molly coating.  I just think it would be (my opinion) a nicer shooting rifle and a bit easier on brass for reloading if I had a mid length gas system barrel on it.

Edited by Gibbs
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Well, I don't think the real "Gibbs" would head slap me for inquiring on improving group sizes.  I think they all do a fine job and it's kind of a Ford - Chevy - Dodge kind of thing.  What one may percieve as BS, the other might find to be the best thing since sliced bread. :)

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You can find lots of talk about slower (looser) twist rates among the benchrest crowd, many saying the same thing Gibbs has stated...albeit a bit differently.

 

A 1:12 or 1:14 twist rate on something like .308 Winchester allows a hotter powder load with heavier bullets, without worrying too much about over pressure issues.

 

Had a retail customer that bought two of the CZ 527s, one of the carbines and a varminter.  He was pulling his hair out trying to find one load for both, called CZ, and they stated (IIRC) the carbine has a 1:8 twist, the varminter a 1:12 twist for these reasons.

 

Apparently the Europeans believe the theory too.

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Gibbs you said

Taking these things into account, there are very nice .308 rifles out there in the AR platform that do exceptionally well with 1:10 twist and 4 or 6 groove rifling. They are, after all, somewhat designed for battle rifle conditions and as such if you look for extreme accuracy, you are better at looking at bolt action .308 over the gas operated semi autos like the AR series.

The barrel I have is not really bad at all. I have been able to get a group at 100 yard of 0.366" using 150 gr Hornady SP bullets non BT with molly coating. I just think it would be (my opinion) a nicer shooting rifle and a bit easier on brass for reloading if I had a mid length gas system barrel on it

outstanding grouping at 100 ! you answered your own question though...outstanding accuracy equals bolt action.....So why dont you try a rainier arms ultramatch grade barrel for your ar platform?.....they come in a middy and they are 6 groove and guaranteed to shoot sub moa....these are not bhw made barrels

so you are plus one on the groove... not to worry :) Wash

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Some info that might be found to be useful :)  http://bisonballistics.com/articles/barrel-twist-and-bullet-stability

Understand that this next link is dealing with 6mm Bench rest. http://www.6mmbr.com/barrelfaq.html   what was interesting is that they talk about using the slowest twist that stabilizes a bullet.  A 1:7 twist and a bullet traveling 3200 fps will give a rotational spin of somewhere near 329,142.86 rpm. ref: http://www.thetruthaboutguns.com/2012/08/foghorn/ask-foghorn-barrel-twist-and-which-is-right-for-your-ar-15/  (read down to "Greg's reply ) I had a friend back in Nebraska that could hand load a 220 Swift so fast that you couldn't hit a target 50 yards away as the bullet would literally spin itself into little dust.  It was hot after the friction of leaving that barrel and the RPM on it was so much that it literally spun itself to pieces in just a few feet. 

 

One thing I have always remembered, and saw examples one time in a gun magazine, was that the tip of the bullet was NOT as critical as the base.  You could deform a tip and still get fairly good accuracy, but you could not deform any part of the base and get by with it.  To prove the point, the magazine handloaded bullets, so that the base entered the lands first and the point of the bullet was in the rear.  Horrible accuracy. :)

 

I hand load and for now I have not found a particular powder, nor load for the 165 grain that gives good consistent accuracy, even though it is a 1:10 twist.  Each barrel is different and when you find a bullet the "barrel" likes, pay attention to it and you can put out dime size groups all day long.  This one seems to really like the 150 gr Hornady.   I had a Saiga .308 that I converted back into the AK -47 style and was very surprised as to how well it liked the 150 gr factory ammo. This is a 5 shot group, shot near dusk.  I thought it was not doing well until I went up to get the target.  Simple Pizza Hut box with a black dot put on it with a magic marker.

308_saiga_rem150psp.jpg

Edited by Gibbs
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  Bullet was probably not hot on that 220 swift , just constructed wrong for the Velocity it was shot at or loaded too hot for bullet construction , same thing.

 

   I have a hard time understanding how the rifling twist rate will change chamber pressure . If same caliber , the barrel will be rifled with spec's for that caliber . I can see its possible , but it won't be much & where are the scientific pressure readings to back this stuff up. 

  There are too many factors involved in chamber pressure , you can get a batch of not to spec bullets or the manufacturer may use a different construction or material , jacket thickness & so on & it will effect chamber pressure & down range velocity , just far too many factors involved to get any good comparison between two barrels .

 

  I have been lucky in getting very good shooting barrels , because I know its not me . <dontknow>

 

  Nice to see another 16" 308 barrel fan.

 

  I find the date on the target in post # 11 ,kinda strange or are you just getting a head start on load testing , 8-10-18  ? <laughs>

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   I have a hard time understanding how the rifling twist rate will change chamber pressure . If same caliber , the barrel will be rifled with spec's for that caliber . I can see its possible , but it won't be much & where are the scientific pressure readings to back this stuff up.

  Nice to see another 16" 308 barrel fan.

 

  I find the date on the target in post # 11 ,kinda strange or are you just getting a head start on load testing , 8-10-18  ? <laughs>

Glad someone paid attention!  LOL  Don't know what I was thinking of on date of 2018!!  It will be edited to reflect the right date of 2014 that's for sure.  Thanks for the catch!!

 

I'll dig you up some info on the twist rate and pressure correlation.  Just might take a bit. :)

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There is so much more to all of this than just the rifling and rate of twist, you have brass prep, oal of cartridge some barrels like a jump of up to 40 thousands, some like to be kissing the lands, a semi auto rifle is not the best choice to shoot 1 hole groups but some will do it , my point is that there is a whole plethora of things that make up a accurate rifle including the shooter, and even more so the trigger... all have a impact on accuracy... I learned experimenting with a Ruger Number 1 action 1 shell at a time trying all different lenghts and oal's powders ,primers, case's. it is a lifelong quest with no one certain answer.... but it is a lot pof fun so enjoy.

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Well, the more I dug the more I found that my argument of faster twist increased chamber pressures.  Appears it is very very minor.  Twist stabilizes longer bullets as they need faster RPM to prevent tumbling or spiraling effects due to imperfection in the bullet.  Shorter bullets, like the 150 Hornady SP (flat bottom) I found to do so well, can be stabilized very well with 1:12 twist, but for heavier (translates to LONGER) bullets, a faster 1:10 or even a 1:9 twist is preferred.  A 1:10 can stabilize 168gr pretty well and might get by with the 175gr but the 190gr or 200gr SPBT would definitely benefit from 1:9 or even 1:8 twist.  The bullet is instable from the point of the base wanting to be in front of the point, and only through sufficient RPM can the gyroscope effect keep the bullet stabilized nose first in flight.  I have read that your best rate of twist is the slowest you need for the bullet you plan to shoot, for optimum accuracy.

 

GOOD links:  http://homepages.solis.co.uk/~autogun/ballistics.htm   http://68forums.com/forums/showthread.php?27991-6-8-SPC-and-Twist-Rate/page5   ,  http://www.frfrogspad.com/intballi.htm  ,  and http://www.thetruthaboutguns.com/2012/08/foghorn/ask-foghorn-barrel-twist-and-which-is-right-for-your-ar-15/

 

Magwa is absolutely correct.  There is much more to rifling and twist.  New brass makes a difference as does brands of brass.  How close is the bullet to the rifling?  How much freebore does the chamber have?  What is the optimum burn for this barrel / bullet combination?  What is the best charge for barrel harmonics and nodes?  That last is a WHOLE new set of circumstance that contribute greatly to rifle accuracy  (barrel harmonics, nodes and shock waves that go back and forth up and down the barrel during the time the bullet is in the barrel).

 

I think I'll stick with a nice mid length gas system, perhaps a 416R steel and 5R button rifling that is available from Brownell's.  It's a nice 1:10 twist and should be a nice barrel easy on the brass and easy on the bolt.

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 Twist stabilizes longer bullets as they need faster RPM to prevent tumbling or spiraling effects due to imperfection in the bullet. 

 

 

That's straight-up NOT the case, right there.

 

 

 The bullet is instable from the point of the base wanting to be in front of the point, and only through sufficient RPM can the gyroscope effect keep the bullet stabilized nose first in flight.

 

 

You got it right, with that - from where ever you found that info.

 

Heavy bullets have to spin faster for that very reason.  Your 168-through-1:10 twist, but 175-not is inaccurate, though.

 

Go research the twist rate on the M110, find out why it was chosen, and what the mandated load for that rifle was.  That'll shake you up.

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According to this link, http://www.thetruthaboutguns.com/2012/08/foghorn/ask-foghorn-barrel-twist-and-which-is-right-for-your-ar-15/  bullets have imperfections that higher RPM, through twist rates, help to negate.

 

Use your logic, then - and the info you found and not what you know.  You contact Hornady and tell them their BTHP Match bullets in the heavier weights need a faster twist, because there are "imperfections in their bullets" that are only known at the higher RPMS that faster twists produce.  That's the reason they need the faster twists - due to those imperfections.

 

Right after you're finished sending off that email, you send another one to Sierra and let them know that exact same information about the imperfections in their MatchKing ammo in the heavier weights.

 

That's just about fucking retarded.  I won't pull any punches letting you know that's about the dumbest $hit I've ever seen posted on a gun forum.

 

Tell Leghorn to get in here and defend what you're saying, about the "imperfection" bull$hit.

 

You're one of those people that can find anything on the internet, read it, try to expound on it - and don't know what the fuk you're talking about at the same time. 

 

Ain't ya?...

Edited by 98Z5V
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 I read that part about the bullet is imperfect & thought the same thing , wonder if the bullet manufacturers know this  <laughs>

 

  You know , all this about getting a couple of CUP from a certain barrel or twist rate is kinda made me think , if thats what someone thinks is keeping them from getting better groups , I believe they have got other problems keeping them from attaining better ones. No doubt that the weight of the bullet can determine the twist rate , to some extent , that is published fact , not to mention has scientific fact surrounding it by long range shooters. 

 

 As has been said , there is far too much that relates to ammo , shooter & the capability of the shooter , that determines how a rifle shoots . The merry go round of what rifling is a better shooter is mote . Getting a good barrel from a reputable manufacturer is ! 

    

  

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