Gunsmithing .308 Barrel Twist Rate...Which to Choose?

[Arc Light]

Given a barrel length of 20" and only shooting bullet weights from 147 to 185 grain, what twist rate would be recommended? From the research I've done, it would seem that a twist rate of 1:11 or 1:12 would work best. Many recommend just going with 1:10 as the best "all around" twist rate. But for the bullet weights I would be shooting it seems that would be too fast of a twist rate?

 

[Steel+Killer]

If most of my shooting was 175 or above I would go 1:10 if it were closer to 150ish I would go 1:12 like all things there is no ONE SIZE FITS ALL....IMO.

 

[Zak Smith]

I shot 1:12's for almost two decades and never had a problem

 

[Steel+Killer]

Yea when I first got into LR I mostly shot 168gr with a 1:12 worked great never had a problem.

 

[PinesAndProjectiles]

If you’re shooting the 185s, is it safe to assume they’re the Berger?

I would run different loads in their bullet twist rate calculator and find something that would at least stabilize these.

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

 

[Arc Light]

If you’re shooting the 185s, is it safe to assume they’re the Berger?

I would run different loads in their bullet twist rate calculator and find something that would at least stabilize these.

Twist Rate Stability Calculator

Our newly updated Twist Rate Stability Calculator not only tells you what your SG is, but it also lets you know if you are reaching your optimized BC.

bergerbullets.com

Thanks for the link.

I don't currently reload, but am seriously considering starting next year when I'll have the room for it. I have a lot of .308 factory ammo, most of it is FGMM and some heavier hunting loads.

 

[FisherT&C]

I have a 20" 308, 10 twist. I've shot 150,155 and 175's through it and all weights shot really well.

 

[PinesAndProjectiles]

Thanks for the link.

I don't currently reload, but am seriously considering starting next year when I'll have the room for it. I have a lot of .308 factory ammo, most of it is FGMM and some heavier hunting loads.

It gives info on bullets other than the Berger if you have the data for them, IE, weights, length, etc.

I forget where I saw it but there’s a lengthy table on the internets that has a majority of bullet info that you can use to populate the twist rate calculator.

 

[308pirate]

Given a barrel length of 20" and only shooting bullet weights from 147 to 185 grain, what twist rate would be recommended? From the research I've done, it would seem that a twist rate of 1:11 or 1:12 would work best. Many recommend just going with 1:10 as the best "all around" twist rate. But for the bullet weights I would be shooting it seems that would be too fast of a twist rate?

1 in 10 is not too fast. 1 in 12 is not too slow.

This is absolutely most over-thought and most insignificant aspect of rifle accuracy.

Pick one and move on.

 

[308pirate]

If most of my shooting was 175 or above I would go 1:10 if it were closer to 150ish I would go 1:12 like all things there is no ONE SIZE FITS ALL....IMO.

A 17" 1 in 12 stabilizes my 178 ELDMs perfectly.

 

[FUNCTIONAL]

I have a 18" 10 twist and a 20" 12 twist. Both shoot 175s to 1k no problem.

If it makes you feel better get 11 twist and split the difference. I would grab whichever I could find quicker from the manufacturers I'd want to use.

 

[hlee]

The only answer worthy of SH is a 1-12 to 1-10 gain twist, left hand twist barrel…

 

[Steel+Killer]

The only answer worthy of SH is a 1-12 to 1-10 gain twist, left hand twist barrel…

Yea, but doesn't that depend on if you use MOA or MILS......

 

[Powder_Burns]

The only answer worthy of SH is a 1-12 to 1-10 gain twist, left hand twist barrel…

I thought the right answer was get both

 

[Arc Light]

I have a 18" 10 twist and a 20" 12 twist. Both shoot 175s to 1k no problem.

If it makes you feel better get 11 twist and split the difference. I would grab whichever I could find quicker from the manufacturers I'd want to use.

Probably what I'll end up doing. 11 Twist seems to work ok for Sako TRG and AI rifles

 

[FUNCTIONAL]

Probably what I'll end up doing. 11 Twist seems to work ok for Sako TRG and AI rifles

My 20" 12 twist is an AI .

 

[Arc Light]

My 20" 12 twist is an AI .

Haha, didn't realize they were offered in a 12 twist. Like @308pirate said, I'm sure I'm overthinking it. Maybe I should flip a coin

 

[pmclaine]

The only answer worthy of SH is a 1-12 to 1-10 gain twist, left hand twist barrel…

This one….

Will be 9.25 to 8.75 LHGT.

Why?

Why not?

 

[Nik H]

My AI AT has a 12 twist. My gas guns have a 10 twist

No issues from either shooting 147-175 grain factory.

 

[FuhQ]

Given a barrel length of 20" and only shooting bullet weights from 147 to 185 grain, what twist rate would be recommended? From the research I've done, it would seem that a twist rate of 1:11 or 1:12 would work best. Many recommend just going with 1:10 as the best "all around" twist rate. But for the bullet weights I would be shooting it seems that would be too fast of a twist rate?

5R rifling for sure, and either 1:8 or 1:9, so you can shoot heavy subtonics, if you want.

If you never plan on shooting subs, or anything heavier than a 220gr bullet in supersonic loads, the 1:10 twist will do just fine.

 

[Rob01]

I wouldn’t go slower than 11. I have used 10, 11 and 12 over the years and now my go to .308 twist is 11. Shoots all the bullets I want it to from 155-178s. Will shoot heavier but I don’t shoot heavier than the 178.

 

[hafejd30]

My AIAT is a 20 1:12 and loves 178 ELDX

Most other 308’s I’ve had were a combo of gas guns and bolts. Most being 1:10. All shot 150-180 very well

 

[338dude]

Given a barrel length of 20" and only shooting bullet weights from 147 to 185 grain, what twist rate would be recommended? From the research I've done, it would seem that a twist rate of 1:11 or 1:12 would work best. Many recommend just going with 1:10 as the best "all around" twist rate. But for the bullet weights I would be shooting it seems that would be too fast of a twist rate?

1in10

 

[Terry Cross]

5R rifling for sure, . . . . .

Why?

.

 

[FuhQ]

Why?

.

Cleans up way easier. I have tons of rifles with Traditional, 5R, and Polygonal style rifling. The 5R and Polygonal rifled barrels deform the bullet Jacket less, which means less copper fouling getting stuck in the bore, which keeps them cleaner longer, and they tend to clean up much faster and easier than the traditionally-cut lands & grooves, when it is time to clean them.

Just my experiences over the last 15 years. Take it for what it’s worth to you.

 

[Terry Cross]

Cleans up way easier. I have tons of rifles with Traditional, 5R, and Polygonal style rifling. The 5R and Polygonal rifled barrels deform the bullet Jacket less, which means less copper fouling getting stuck in the bore, which keeps them cleaner longer, and they tend to clean up much faster and easier than the traditionally-cut lands & grooves, when it is time to clean them.

Just my experiences over the last 15 years. Take it for what it’s worth to you.

Understood.
Everything you wrote is the same as what the internet widely agrees upon and it looks good on paper.

That has not been my experience at all over the last 35 years and roughly 3,700 .308 Win. barrels.

With all other things being equal, I have not found any difference in speed, longevity, ease of cleaning, tendency to foul or accuracy.

I have no reason to poo poo 5R.
I have chambered a lot of 5Rs from Boots, Rock, Broughton, Bartlien and a few from Kreiger.
All performed excellently but no different than the traditional 4 groove Kriegers.

5R barrels from Bartlein, Krieger and a handful of other makers are exceptional, but they are exceptional because they are made right by badass craftsmen, not because they are 5R.

.

 

[rtB]

11.25" twist 19.5" barrel is the perfect setup. Left twist in Australia.

 

[FuhQ]

Understood.
Everything you wrote is the same as what the internet widely agrees upon and it looks good on paper.

That has not been my experience at all over the last 35 years and roughly 3,700 .308 Win. barrels.

With all other things being equal, I have not found any difference in speed, longevity, ease of cleaning, tendency to foul or accuracy.

I have no reason to poo poo 5R.
I have chambered a lot of 5Rs from Boots, Rock, Broughton, Bartlien and a few from Kreiger.
All performed excellently but no different than the traditional 4 groove Kriegers.

5R barrels from Bartlein, Krieger and a handful of other makers are exceptional, but they are exceptional because they are made right by badass craftsmen, not because they are 5R.

.

I never denied any of that, did I? And I agree with everything you said. I never said they were faster, or more accurate, because that is BS. I have traditional barrels that are absolute 1-hole tack-drivers. We are on the same page. I’ve been shooting WAY longer than 15 years (30 years), just haven’t been using 5R and Polygonal since before then.

 

[Terry Cross]

I never denied any of that, did I? And I agree with everything you said. I never said they were faster, or more accurate, because that is BS. I have traditional barrels that are absolute 1-hole tack-drivers. We are on the same page. I’ve been shooting WAY longer than 15 years (30 years), just haven’t been using 5R and Polygonal since before then.

No wories.
I didn't try to put words in your mouth.
I simply asked why, you said "5R rifling for sure, . . . . ."

That was a pretty emphatic statement used to steer the OP., yet nothing tangible was put forth to state why.

You said 5R fouls less, stays clean longer and cleans up faster.
Less, longer and faster than a traditional bore profile from the same or equal maker that you have personally experienced?

I'm simply relaying that has not been my experience.
Thus we are not on the same page.
Does not make you bad or me good. Just owners of different observations.

.

 

[ratton]

My XM-3 Clone 18.5 inch barrel has a 1/10 twist and shoot 150 to 200 grain 30 cal bullets just fine.

 

[longebow]

Arc Light:

I am making the assumption that you are asking about the twist rate for the .308 Winchester/7.62 x 51 mm NATO cartridge.

If so, you ask a question that I've pondered since the mid-70's. I'm not a ballistician, a rocket scientist, bullet manufacturer or professsional (ie sponsered) shooter. I'm just an old school rifleman who was mentored by the likes of Frank White (Fort Campbell), Gerald "Hook" Boutin (Fort Benning) with guest appearances by Washington State riflemen Gary Rasmussen and Bud Solis, and USAMU greats like Emil Praslick...

BLUF: 1/10"

Yes, it is true that any twist rate for the .308 Winchester from 1-10 to 1-12 will stabilize most common bullets between 147 and 185 grains. In my research, reloading and shooting experience out to 1000 yards, the faster twist rate reduces the variabiliy seen at the longer ranges. This is even more apparent to me when using bullets of the secant ogive shape (VLD, Bergers, etc) vs the tangent ogive shape (Sierra, Lapua, etc). In my experience, secant ogive bullets need "more" spin (which is actually another way of describing RPM), as velocity plays a role in this equation. Thus, my clarification of .308 Win, as .30 caliber magnums are a different animal due to their higher velocities.

I hope that his helps.

longebow

 

[longebow]

I would like to amend the above, as my memory is not as crisp as it used to be...

It was JOE White (SFC, US Army (retired), sniper in the RVN, and lead instructor of the 101st Division Sniper school in the late 80's). RIP Brother!

FRANK White of Compass Lake Engineering was my go to guy for my AR service rifle barrels when I was burning through them to earn my President's Hundred Tab and Distininguished Rifleman's Badge.

Sorry...

longebow

 

[moosemeat]

11.25. Worked for the M24.

 

[Arc Light]

I ended up going 1:11 twist, figured that would be ideal given the bullet weights I intend to use. Now just gotta find a smith to install it for me.

 

[Zak Smith]

This is even more apparent to me when using bullets of the secant ogive shape (VLD, Bergers, etc) vs the tangent ogive shape (Sierra, Lapua, etc). In my experience, secant ogive bullets need "more" spin (which is actually another way of describing RPM), as velocity plays a role in this equation. Thus, my clarification of .308 Win, as .30 caliber magnums are a different animal due to their higher velocities.

The rate of twist depends on the amount of transverse force on the front of the bullet at its center of drag rotated around its center of mass, compared ("divided by") the amount of resistance to this turning that the rotational inertia of its spinning provides.

The first term (the transverse "turning") torque depends on the length of the bullet, the location of its center of mass, and how much frontal drag it has.

The second term (rotational inertia) depends on the mass distribution as a function of distance along the radius from the bullet centerline and the rpm.

 

[Alaska]

1:12 = 130 to 168
1:10 = 150 to 200
1:9 = 220 to 230
Suggest 1:10 in 5R

GA Precision is a great place to start

 

[Alaska]

I would like to amend the above, as my memory is not as crisp as it used to be...

It was JOE White (SFC, US Army (retired), sniper in the RVN, and lead instructor of the 101st Division Sniper school in the late 80's). RIP Brother!

FRANK White of Compass Lake Engineering was my go to guy for my AR service rifle barrels when I was burning through them to earn my President's Hundred Tab and Distininguished Rifleman's Badge.

Sorry...

longebow

Frank White help me build my MK 12 Mod 0 about 2010

 

[Halcyonhal]

11.25" twist 19.5" barrel is the perfect setup. Left twist in Australia.

Left twist due to the antipodean coriolis effect?

 

[AccuSol-ERN]

I disagree. I have been chambering 6mm, 6.5mm, and 30cal 4 groove barrels and they are definitely my preference from a machining standpoint. I am not saying 5R are bad......I AM saying I get measurably better results with a 4 groove with my chambering setup. Is this measurable difference going to make a difference on target maybe? maybe not?........but it sure makes me feel better as a machinist.

To the OP.......ALL 308 barrels I do are 1:9 or faster. I have worked with a lot of shooters who have extensive trigger time on pushing the 308 way past its understood limit and the extra twist really benefits them without sacrificing anything closer.

Your call but I definitely wouldn't go slower than 1:10.

Ern

 

[XP1K]

I'll drag this one back to the top for a minute. I was going to post a similar thread then I found this one.

I think the time has come to rebarrel my 308 700LTR. It'll still hammer out to 600 but it starts getting really wild around 750. It never has cared for anything at or above the 175gr range in bullets but it loves a 168smk and it's done pretty well with a 155 Amax. Out to 750ish. Past that it goes nuts.

Around 800 it struggles to hit C zone size steel and out to 1000 you're looking at about 5-6 moa with the 155's that are routinely under half moa at 100. I don't rember my muzzle velocity but it was close to 2800fps I believe from its factory 20" barrel.

So here's my dilemma, what twist to I go with. Looking through this thread it looks like anything in the 10-12 should do just fine. Would it hurt anything to go faster ? I don't shoot lite bullets from this gun.

I had a 16" 1:8 lilja that started life as a 300blk when it first came out but it wasn't long until I lost interest in that thing and I had it rechambered to 308. It shot factory 168gr hornady match into one hole at 100 yards. Sold that rifle to my cousin and his favorite load for it is the precision hunter 178. I've tried to buy that rifle back from him a half dozen times but he ain't having it.

So going off of past experiences with a sample size of one, the faster twist is appealing to me at the lower velocity of a 20" barrel. Seems like it would give better stability at distance, or am I wrong in my line of thinking there ?

 

[Alaska]

1-10 is great 5R would be good !
With 175 MK
1-12 is good with 150 to 168gr !
20” minimum OK threaded
Prefer 22” to 24” non threaded in 308 win

Krieger top pick number 5 weight perfect in 22 “

 

[XP1K]

I may stretch it to 22" it's a full time suppressor host so I like to keep it short.

 

[AccuSol-ERN]

I would go with a 9twist 4groove (my preference). Don't listen to fast twist limiting light bullets too. I shoot a 10twist 300wsm with 110gr vmax at 3870ish on crows and coyotes (200-300yds) and it is downright explosive. I don't like lobbing heavy bullets that buzz through animals and skip off the ground unless I am at a bermed range.

I've had similar results with light varmint bullets in fast twist 223s, 22-250s, 243s, etc. too.

Ern

 

[pmclaine]

This one….

Is 9.5:1 to 8.75:1 left hand, even gain twist at 21 inches.

I have no idea how it shoots it’s still getting hand love….

 

[XP1K]

This one….

View attachment 8010238
View attachment 8010236

Is 9.5:1 to 8.75:1 left hand, even gain twist at 21 inches.

I have no idea how it shoots it’s still getting hand love….

View attachment 8010241

Walnut ? Pretty grain.

 

[XP1K]

I would go with a 9twist 4groove (my preference). Don't listen to fast twist limiting light bullets too. I shoot a 10twist 300wsm with 110gr vmax at 3870ish on crows and coyotes (200-300yds) and it is downright explosive. I don't like lobbing heavy bullets that buzz through animals and skip off the ground unless I am at a bermed range.

I've had similar results with light varmint bullets in fast twist 223s, 22-250s, 243s, etc. too.

Ern

I found a 9 twist bartlein m24 at Altus in stock. I may just pull the trigger on it. Cut at 20" it's gonna be thick on the muzzle end lol.

 

[pmclaine]

I found a 9 twist bartlein m24 at Altus in stock. I may just pull the trigger on it. Cut at 20" it's gonna be thick on the muzzle end lol.

Thicc is good.......M24 is like pencil diameter.

 

[AccuSol-ERN]

I found a 9 twist bartlein m24 at Altus in stock. I may just pull the trigger on it. Cut at 20" it's gonna be thick on the muzzle end lol.

Yep. We use a lot of 9twist 30cal from 308win to 300prc. In my opinion, 9twist is the new 10twist.......after all bullets are not getting any shorter or lighter.

Ern

 

[Oryx]

No wories.
I didn't try to put words in your mouth.
I simply asked why, you said "5R rifling for sure, . . . . ."

That was a pretty emphatic statement used to steer the OP., yet nothing tangible was put forth to state why.

You said 5R fouls less, stays clean longer and cleans up faster.
Less, longer and faster than a traditional bore profile from the same or equal maker that you have personally experienced?

I'm simply relaying that has not been my experience.
Thus we are not on the same page.
Does not make you bad or me good. Just owners of different observations.

.

Terry, Just curious what your thoughts would be for the ideal barrel set up for a long range 308 based on your experience..... barrel brand, rifling, twist, chamber incl. throat, barrel length , etc.. Using 155/168/178 variants

 

[Bender]

Understood.
Everything you wrote is the same as what the internet widely agrees upon and it looks good on paper.

That has not been my experience at all over the last 35 years and roughly 3,700 .308 Win. barrels.

With all other things being equal, I have not found any difference in speed, longevity, ease of cleaning, tendency to foul or accuracy.

I have no reason to poo poo 5R.
I have chambered a lot of 5Rs from Boots, Rock, Broughton, Bartlien and a few from Kreiger.
All performed excellently but no different than the traditional 4 groove Kriegers.

5R barrels from Bartlein, Krieger and a handful of other makers are exceptional, but they are exceptional because they are made right by badass craftsmen, not because they are 5R.

.

No, they are more accurate because they said so. 5R definitely was not a hyped marketing ploy to sell more stuff. This is the gun community, we are smarter than falling for these low iq tricks.