BARREL TWIST RATE.308?

[JJ109]

So my buddy wants to buy a.308 BHW 20 " barrel with fluting done at 1/9.73 twist rate. He plans on shooting between 168 to 178 bullets with this gun. He wants to try to use the 175 SMK if possible because he buying the same scope i am. That is the base load on the scope he wants to buy.

What your guys thoughts on this?

I told him he should look at the 1/11 twist instead.  BHW is saying that good but it doesnt sound right to me. 

[Tripledeuce]

The difference between a standard 1-10 and 1 -9.73  is about as much as spit is worth!

 go with a 1-9 or 1-9.5 at the most. and it should be about right for the 175's.

 Respectfully

Terry

Edited September 20, 2016 by Tripledeuce

[Robocop1051]

I was sure that 1:10 was fine for 175's. My CF barrel is 1:10 although I haven't stretched past 300 yards with it yet either... and my only 175's are SP hunting loads. 

[JJ109]

7 hours ago, Tripledeuce said:

The difference between a standard 1-10 and 1 -9.73  is about as much as spit is worth!

 go with a 1-9 or 1-9.5 at the most. and it should be about right for the 175's.

 Respectfully

Terry

Gotcha. He is doing his build soon and ordering the barrel soon. I went 1/11 3 polygon rifling cause BHW told me it should shoot anything between 168's to 180' well and 175's very good. I thought that 1/9.73 twist would be better for 180's and higher

[planeflyer21]

6 hours ago, Robocop1051 said:

I was sure that 1:10 was fine for 175's. My CF barrel is 1:10 although I haven't stretched past 300 yards with it yet either... and my only 175's are SP hunting loads. 

I'm not aware of any production bolt-action rifles that use anything tighter than a 1:10 twist for .308 Win.  Seem like they would be all over tighter twists if it made a difference.

[Robocop1051]

I know the .300blk is twisted to 1:9 or 1:8 for those extra heavy subs. I've actually never seen a .308 loaded past 180gr, even though I know theyou make them way past 200gr.

[EngrBob]

My Faxon 1:10 .308 barrel loves the 168 and 175 grain projectiles.

[survivalshop]

  I guess shooting range may have something to do with twist rate & Bullet weight being used & type of Bullet , will have something to do with it . I know I have heard of people who are not pleased with 1-11.5 , using 150 gr. loaded ammo ,that twist rate may like the heavies better , hard to say , too many variables .

  We know a 1-10 works great on a host of rifles & Bullet configurations .

[JJ109]

1 hour ago, survivalshop said:

  I guess shooting range may have something to do with twist rate & Bullet weight being used & type of Bullet , will have something to do with it . I know I have heard of people who are not pleased with 1-11.5 , using 150 gr. loaded ammo ,that twist rate may like the heavies better , hard to say , too many variables .

  We know a 1-10 works great on a host of rifles & Bullet configurations .

I knew I was probably going to shoot 168's and higher when i built my rig, but what the heck i could always just see how the lighter grain ammo shoots.

[mrmackc]

1 in ten works for me in .308, but I am not too pickie.

[survivalshop]

  I have shot 155's ,168's & 175's with 16', 18' & 20 " 1-10 Barrels & all shoot fine , very good groups ,mine are all  S/S Criterion Barrels , but I'm not shooting 800-1K , someone else will have to chime in at those ranges .

[JJ109]

Yea I have some practicing to do before i can think i shoot out to a 1000 yards. But is that the fun part going out for the practicing? LOL

[mrmackc]

Getting ready is what makes the difference between having a stressful day and a feeling of accomplishment , well sometimes. 

[98Z5V]

On 9/20/2016 at 2:53 AM, JJ109 said:

Gotcha. He is doing his build soon and ordering the barrel soon. I went 1/11 3 polygon rifling cause BHW told me it should shoot anything between 168's to 180' well and 175's very good. I thought that 1/9.73 twist would be better for 180's and higher

There are very few 180s that you can even load to magazine-length.  Most 180s, you can't. 

On 9/20/2016 at 5:37 AM, Robocop1051 said:

I know the .300blk is twisted to 1:9 or 1:8 for those extra heavy subs. I've actually never seen a .308 loaded past 180gr, even though I know theyou make them way past 200gr.

^^^  He said it...  Those .308" projectiles that go up to 225gr are for different calibers, mainly.  Think 300 Win Mag, and the sort.

 

Hornady DOES make a 198gr HPBT that you can load to mag length, and a 200gr ELD-X that you can load to mag length...  Here's the 200 load data:

 

ReloadingData308Win200grELDX.pdf

A 1:10" twist should shoot both of those ^^^ just fine. The original, optimal twist rate for 175s from a gas gun was determined to be 1:11.25", by KAC, and used on the M110 production rifles. 

Edited September 24, 2016 by 98Z5V

[Sisco]

Just a thought: The tighter you make the barrel twist, the less performance you will probably get out of lighter weight bullets. My 1 in 10 does ok with 147 gr. M80's, my 1 in 11.25 does a little better. My pocket book tells me I will shoot a lot of M-80, if for no other reason then to get the brass for reloading. Going to 1 in 9 might rule out using the cheap stuff for anything but plinking or mag dumps. Maybe some of the more knowledgeable guys can weigh in on this.

[JJ109]

8 hours ago, 98Z5V said:

There are very few 180s that you can even load to magazine-length.  Most 180s, you can't. 

^^^  He said it...  Those .308" projectiles that go up to 225gr are for different calibers, mainly.  Think 300 Win Mag, and the sort.

 

Hornady DOES make a 198gr HPBT that you can load to mag length, and a 200gr ELD-X that you can load to mag length...  Here's the 200 load data:

 

ReloadingData308Win200grELDX.pdf

A 1:10" twist should shoot both of those ^^^ just fine. The original, optimal twist rate for 175s from a gas gun was determined to be 1:11.25", by KAC, and used on the M110 production rifles. 

Thanks for the info 98z5v.

Buddy is trying to build 308 caliber gas gun to go out to 1000 plus yards. Which is all well and fine but there is no range that i know of close to me that even goes that far. Tried to explain that adding a 20" build will be adding some weight. 

Ill be happy when i can start shooting 600 yards good 

[Robocop1051]

I built an 18" Mega/SI-D rifle for a buddy. He banged steel at 1k with it.

[JJ109]

4 hours ago, Robocop1051 said:

I built an 18" Mega/SI-D rifle for a buddy. He banged steel at 1k with it.

I would love to get the opportunity to do that one day but, the longest range i know of in my area is 600 yards. My local range i belong to goes out to 300 yards. 

[Pa_farmboy]

On 9/20/2016 at 7:33 AM, planeflyer21 said:

I'm not aware of any production bolt-action rifles that use anything tighter than a 1:10 twist for .308 Win.  Seem like they would be all over tighter twists if it made a difference.

The first run of 308 savage hog hunters have a 20 inch medium profile barrel with a 1/9 twist rate. It's also threaded for a suppressor. The 1/9 is nice for stabilizing heavy rounds used to drop hogs and really good for stabilizing subsonic loads (even heavy subsonic loads ). I haven't experimented to much with hand loads (other than subsonic loads) but so far heavier loads are what she likes. I've stayed under 200gr but it stabilizes and holds good groups up to those weights and keeps tight with 165-170 gr subsonic loads. So if your wondering why a 1/9 twist would be beneficial the answer is heavy loads for aggressive game such as hogs and heavier suppressed loads would be my answer. Ive focused on my rem 700 since I've had the hog hunter but I'm currently making my changes to her and I'm about to get to know her much better. I'll have better info after but I'm honestly interested in seeing what she is capable of. 

[Pa_farmboy]

On 9/24/2016 at 8:30 AM, Sisco said:

Just a thought: The tighter you make the barrel twist, the less performance you will probably get out of lighter weight bullets. My 1 in 10 does ok with 147 gr. M80's, my 1 in 11.25 does a little better. My pocket book tells me I will shoot a lot of M-80, if for no other reason then to get the brass for reloading. Going to 1 in 9 might rule out using the cheap stuff for anything but plinking or mag dumps. Maybe some of the more knowledgeable guys can weigh in on this.

The faster twist rate can spin the lighter faster loads so fast that centrifugal force will literally tear the bullet apart before it reaches the target. You can counter this with heavier jackets and fmj but that doesn't work well for hunting. The other option is heavier bullets or slowing your loads down. 

A hot 5.56 load can spin the bullet in excess of 40,000 rpm on a 1/9 twist. 

[Sisco]

This thread is near five years old.

[DNP]

But still relevant. 

[TPO]

There are several factors that go into determine optimal twist rate for a rifle. They are bullet weight, bullet bearing surface, bullet jacket thickness, bullet velocity and weather.

In general you want a twist rate that will tend towards barely stabilizing your bullet for the best accuracy. A fast twist barrel will shoot all weights and velocities of bullets. A slower twist barrel will shoot more accurately but may not stabilize all weights and velocities of bullets. If you plan on shooting a range of bullet weights say 150-200gr I would go with the 10 twist. If you are going to shoot lighter bullets say in the 110-150gr. consider a 12 twist barrel. If you barely stabilize a bullet with a large bearing surface say a FB bullet with a round nose then if you change to a low bearing surface bullet say a BT 11+ ogive VLD it may not stabilize. The faster the velocity of your load the heavier the bullet you can stabilize. Weather plays into this. Cold can cause instability in marginally stabilized bullets. Bullet jacket thickness is important in that some thin jacketed bullets may fly apart at increased velocities +/or twist rates. I have only heard of this happening in varmint rifles with thin jacketed bullets going at high velocity. I have no experience varmint hunting with a .308 (but I would consider it). 

[DNP]

Great post. 

[TPO]

Thank you Mr. DNP. I assume you are a Mr. I would hate to have triggered some one of the 28+alternate genders out there now. The exception is women. I consider them a separate species.