Twist Rate for 230gr in 308

[APGE]

I'll preface this post by saying that this is an experiment. The newest 230gr offerings from Sierra and Hornady have respectable enough BCs to give a material increase in wind bucking over a 200.20x. Mastering the gun handling to get decent vertical in an ftr rifle may be an issue, but I'm curious enough to try it.

Now for my conundrum;
Sierra recommendeds a 1:8 twist barrel, Hornady a 1:9. I don't think either manufacturer considered they're target market to be the 308w when devising these recommendations.

I'm thinking an 8 twist is my safest option, however using Bergers twist rate calculator and putting in the figures for the 230 smk, a 9 twist gives an sg of 1.48 at 2450fps.

If this experiment fails, I will likely rechamber the barrel to fire 215s or 220s. If it works, I will save the a tips for matches and shoot the (much) more affordable 225 eldms at club level.

Two questions for the brainstrust;

Will an 8 twist over spin the Berger options if I rechamber?

Will a Hornady 225 eldm lose jackets from an 8 twist at 2450fps?

Thanks y'all

 

[avidflyer]

need to verify formula but if I remember correctly 2450x720/twist keep it under 300,000 should be ok

 

[284winner]

I'll preface this post by saying that this is an experiment. The newest 230gr offerings from Sierra and Hornady have respectable enough BCs to give a material increase in wind bucking over a 200.20x. Mastering the gun handling to get decent vertical in an ftr rifle may be an issue, but I'm curious enough to try it.

Now for my conundrum;
Sierra recommendeds a 1:8 twist barrel, Hornady a 1:9. I don't think either manufacturer considered they're target market to be the 308w when devising these recommendations.

I'm thinking an 8 twist is my safest option, however using Bergers twist rate calculator and putting in the figures for the 230 smk, a 9 twist gives an sg of 1.48 at 2450fps.

If this experiment fails, I will likely rechamber the barrel to fire 215s or 220s. If it works, I will save the a tips for matches and shoot the (much) more affordable 225 eldms at club level.

Two questions for the brainstrust;

Will an 8 twist over spin the Berger options if I rechamber?

Will a Hornady 225 eldm lose jackets from an 8 twist at 2450fps?

Thanks y'all

No real world experience here with those heavies in a .308 BUT from close buddies experiences, I think the 8 twist is the safe route. You won't turn enough velocity to turn too much RPMs. The slower speeds will need the faster barrel. Kinda like the .223 pushing 90/95s.

 

[XTR]

@APGE Good luck. This has been tried by many good shooters since at least 2013 that I know of, and none of them won with them. That's not to say that you're not going to find the magic sauce. Hey, I've dropped few thousand on barrels and bullets for experiments in the past myself, learning can be fun (and sometimes frustrating)

 

[Acyr]

I had a lot of fun experimenting with 230's in a 308. Shot 1642 of them to date.
I use a .300/.308 8.8 twist 34 inch tube. 9 twist will be fine.
A-Tips worked best, Palma brass, CCI450, 3.391 COAL, H4350, 20 off, 2500 fps.
Sierra's were pretty good, Bergers not so much.

 

[Medic505]

I had a lot of fun experimenting with 230's in a 308. Shot 1642 of them to date.
I use a .300/.308 8.8 twist 34 inch tube. 9 twist will be fine.
A-Tips worked best, Palma brass, CCI450, 3.391 COAL, H4350, 20 off, 2500 fps.
Sierra's were pretty good, Bergers not so much.

What bullet did you shoot at the SWN's this year Andy?
Dean

 

[Acyr]

What bullet did you shoot at the SWN's this year Andy?
Dean

I used 200 Hybrids first 2 days. 230 A-Tips the last day.
I shot 230 A-Tips during the AZ State 600, 1000 and Palma Championships.

 

[Ned Ludd]

I have a .308 Win F-TR load with 215 Hybrids at ~2550 fps out of a 30" 10-twist barrel. The predicted Sg (70 deg F, 1000 ft elevation) using Berger's twist rate calculator is 1.48. The most important thing is that they shoot just fine. Until you are under-spinning a bullet such that the predicted Sg drops down into the 1.3 or even 1.2 range, it's not a big stability issue. The effective amount of intrinsic BC given up is relatively minor for predicted Sg's between 1.40 and 1.50. In fact, they're really not worth any concern. When you get down in the 1.20 or 1.25 up to 1.35-ish range, the bullet is giving up a pretty substantial amount of the intrinsic BC. However, most bullets will still be gyroscopically stable at those Sg's. Bullets generally will not display noticeable stability issues such as oblong holes in the targets or even key-holing until the predicted Sg is around 1.1 or lower.

I also ran the numbers for the 230s out of a 9-twist barrel at 2450 fps (60 deg F, 500 ft elevation) as shown below. You will be just fine. FWIW - Berger's twist rate calculator by is set by default at 59 degrees F, 0 ft elevation. These are very conservative default settings. Unless you're planning on shooting at the beach in San Diego in January, use the elevation and approximate average temperature where you shoot most often as inputs.

 

[BronzeArcher]

I wouldn't worry about over spinning the bullet with a 1 in 8" twist.

However, the heavy bullets in a faster twist rate will exert greater torque on the barrel on the ride down, thus greater torque on the rifle.

That torque on the rifle is going to tend to move things before the bullet leaves the barrel. All other factors being equal, the rifle with the faster twist requires greater shooting discipline in hold and recoil management to keep the motion of the rifle as close as possible to the same every time.

In that torque range, faster twist rifles are harder to shoot with great precision.

 

[Dessert]

If I remember correctly, David Tubb used Sierra 250 grain matchking in the 308 to win the long range championships at Perry can’t remember what year exactly. I still have a box in a futile attempt to shoot them. Brass would only last one shot. I was trying a 7 twist. Don’t know what his was.

 

[APGE]

I used 200 Hybrids first 2 days. 230 A-Tips the last day.
I shot 230 A-Tips during the AZ State 600, 1000 and Palma Championships.

Did you feel that the wind bucking benefits outweighed the gun handling drawbacks? What was your vertical like?

 

[APGE]

I have a .308 Win F-TR load with 215 Hybrids at ~2550 fps out of a 30" 10-twist barrel. The predicted Sg (70 deg F, 1000 ft elevation) using Berger's twist rate calculator is 1.48. The most important thing is that they shoot just fine. Until you are under-spinning a bullet such that the predicted Sg drops down into the 1.3 or even 1.2 range, it's not a big stability issue. The effective amount of intrinsic BC given up is relatively minor for predicted Sg's between 1.40 and 1.50. In fact, they're really not worth any concern. When you get down in the 1.20 or 1.25 up to 1.35-ish range, the bullet is giving up a pretty substantial amount of the intrinsic BC. However, most bullets will still be gyroscopically stable at those Sg's. Bullets generally will not display noticeable stability issues such as oblong holes in the targets or even key-holing until the predicted Sg is around 1.1 or lower.

I also ran the numbers for the 230s out of a 9-twist barrel at 2450 fps (60 deg F, 500 ft elevation) as shown below. You will be just fine. FWIW - Berger's twist rate calculator by is set by default at 59 degrees F, 0 ft elevation. These are very conservative default settings. Unless you're planning on shooting at the beach in San Diego in January, use the elevation and approximate average temperature where you shoot most often as inputs.

View attachment 1185889

View attachment 1185890

While I agree that that's a stable combination, without doubt, if you run the same figures at sea level with a 1.76" length (atip) or 1.715" (Sierra), the numbers aren't as comforting.

 

[Ned Ludd]

While I agree that that's a stable combination, without doubt, if you run the same figures at sea level with a 1.76" length (atip) or 1.715" (Sierra), the numbers aren't as comforting.

Not that many people shoot at (or close) to sea level. Obviously if you do then it's a concern.

 

[APGE]

Not that many people shoot at (or close) to sea level. Obviously if you do then it's a concern.

A few times a year it is - one local range is 100 feet ASL

 

[Ned Ludd]

A few times a year it is - one local range is 100 feet ASL

The primary issue with what you're attempting to do is that it's highly questionable whether you will end up satisfied with the performance you get from any of those bullets. There's a very good reason no one is using them in F-TR. If you order an 8-twist barrel throated from here to Sunday to accommodate those long bullets and you don't like the way they shoot, you'll end up with a barrel that is really not optimal for anything else. Having been there and done that on more than one occasion, my only advice is to think it through very carefully.

 

[Acyr]

Did you feel that the wind bucking benefits outweighed the gun handling drawbacks? What was your vertical like?

Some may find it hard to believe but I had no issues with vertical. It is a consistent .7 moa gun. Not as accurate as my 200 loads but pretty decent for sure. I have cleaned 600 multiple times and shot 198's & 199's at 1000 with it. I use a tuned RAD on Mcmillan benchrest stock. Tracks awesome with no more hop than my Xit's. In a more capable shooters hands it would be deadly. In my hands not so much lol. Wind reading is still the key. If you can't read the wind these wont help you.

 

[Ray123]

I'll preface this post by saying that this is an experiment. The newest 230gr offerings from Sierra and Hornady have respectable enough BCs to give a material increase in wind bucking over a 200.20x. Mastering the gun handling to get decent vertical in an ftr rifle may be an issue, but I'm curious enough to try it.

Now for my conundrum;
Sierra recommendeds a 1:8 twist barrel, Hornady a 1:9. I don't think either manufacturer considered they're target market to be the 308w when devising these recommendations.

I'm thinking an 8 twist is my safest option, however using Bergers twist rate calculator and putting in the figures for the 230 smk, a 9 twist gives an sg of 1.48 at 2450fps.

If this experiment fails, I will likely rechamber the barrel to fire 215s or 220s. If it works, I will save the a tips for matches and shoot the (much) more affordable 225 eldms at club level.

Two questions for the brainstrust;

Will an 8 twist over spin the Berger options if I rechamber?

Will a Hornady 225 eldm lose jackets from an 8 twist at 2450fps?

Thanks y'all

No problem with the 8 twist in 308, it shoots all Serria 200 smk cn, 230smk cn plus 200.2 berger in small groups, never had a bullet failure in 308 with any bullet... also have a 9 twist that likes the 200 SMK. The 8 twist is the way to go... The only bullet I ever had fail in flight was the 30 grain Berger in 17 Remington it would come apart about 80 yards out, but really nasty on close range ground squirrels.

 

[paulT]

Some may find it hard to believe but I had no issues with vertical. It is a consistent .7 moa gun. Not as accurate as my 200 loads but pretty decent for sure. I have cleaned 600 multiple times and shot 198's & 199's at 1000 with it. I use a tuned RAD on Mcmillan benchrest stock. Tracks awesome with no more hop than my Xit's. In a more capable shooters hands it would be deadly. In my hands not so much lol. Wind reading is still the key. If you can't read the wind these wont help you.

Do you hold Rifle stock forend when shooting the 230s to help keep torque recoil under control.

 

[Acyr]

No, I never hold the stock forend. Position and rifle balance is key to mitigating rifle hop.

 

[paulT]

No, I never hold the stock forend. Position and rifle balance is key to mitigating rifle hop.

Could you share Rifle set up
Grip meathod you use to control torque and rifle hop when shooting 200+ grain weight bullets for .308, Thanks.