1:7 Twist on .308?

[BigTimeMediocrity]

Hey guys,

Looking to put a prefit on my T3X in .308. I'm looking at one of the tightest twist options from IBI (1:7) to hopefully give me a higher BC and stability out past transonic.

I mostly intent to shoot 168-178gr handloads, with the odd hunting round.

Does anyone have any more insight into this?

 

[Criver600]

Not how it works. Twist rate stabilizes the bullet at muzzle velocity. Rpm of the projectile does not fall off as rapidly as velocity. Excessive rpm (twist) will not let your bullet tip over, (follow the curve) whatever you want to call it screwing up your theoretical BC. How a bullet passes through the transonic zone depends on its design. It gets most of them

 

[spife7980]

I’d stick with 9 or 10 for the weights you mentioned. Those fast 7 twist are for subsonics mostly, may shoot nicely but the 10s a standard for a reason.
Some are using them for super heavy bullets in magnums etc as well.

 

[BigTimeMediocrity]

Not how it works. Twist rate stabilizes the bullet at muzzle velocity. Rpm of the projectile does not fall off as rapidly as velocity. Excessive rpm (twist) will not let your bullet tip over, (follow the curve) whatever you want to call it screwing up your theoretical BC. How a bullet passes through the transonic zone depends on its design. It gets most of them

I suppose I worded it wrong. What I meant is wouldn't a faster twist give me more stability out to increased ranges, resulting in less degradation of your BC, therefore a better flight.

In other words, would there be any negatives to a 1:7 twist.

 

[phlegethon]

I suppose I worded it wrong. What I meant is wouldn't a faster twist give me more stability out to increased ranges, resulting in less degradation of your BC, therefore a better flight.

In other words, would there be any negatives to a 1:7 twist.

Yes. The faster you spin bullets, the more you see the effects of flaws related to asymmetry (jackets not perfectly uniform, uneven distribution of flaws in cores). So accuracy will be degraded. It’s also possible to over stabilize bullets such that they no longer perfectly follow the downward slope of the flight path, increasing drag. And they can blow up if spun too fast, though this is unlikely with a 308.

 

[BigTimeMediocrity]

I’d stick with 9 or 10 for the weights you mentioned. Those fast 7 twist are for subsonics mostly, may shoot nicely but the 10s a standard for a reason.
Some are using them for super heavy bullets in magnums etc as well.

Would there be any downsides to a tighter twist? If so what would they be? Ive just heard that its been proven that there's no downside to faster twists anymore, but I can't find much info on it

 

[BigTimeMediocrity]

Yes. The faster you spin bullets, the more you see the effects of flaws related to asymmetry (jackets not perfectly uniform, uneven distribution of flaws in cores). So accuracy will be degraded. It’s also possible to over stabilize bullets such that they no longer perfectly follow the downward slope of the flight path, increasing drag. And they can blow up if spun too fast, though this is unlikely with a 308.

Thanks for the solid reply. I'll do a little more research and maybe reconsider.

 

[supercorndogs]

If you want a higher B.C choose a different caliber. Choosing a flying pig, then working about ballistic minutiae from twist rate is going to gain you anything noticeable.

 

[A&8's]

Only time I would consider a 7 twist in 308 would be if the free bore was lengthened to allow for longer, higher BC 30 cal bullets. There are a few guys on here shooting a mile+ with 308 and 215g bullets, using fast twist rates.

 

[Criver600]

I suppose I worded it wrong. What I meant is wouldn't a faster twist give me more stability out to increased ranges, resulting in less degradation of your BC therefore a better flight.

In other words, would there be any negatives to a 1:7 twist.

No, if your projectile is "stabile" at muzzle velocity, as the velocity falls off its spinning much faster than it needs to, excessive twist will not let the bullet "tip" at the apex of its trajectory degrading BC. Bigger bullets is the quick answer

 

[308pirate]

Would there be any downsides to a tighter twist? If so what would they be? Ive just heard that its been proven that there's no downside to faster twists anymore, but I can't find much info on it

Go get a 1 in 5 then and show us

 

[4thandbleek]

I have a 1-7 twist on my 308 and a 14inch barrel. 11.5 gr of TB puts me at 1041 fps with 208 gr. I also get 2407 fps with 44 gr. BLC2 with 168 gr. match. I have a GemTech that I run on it.

 

[DJL2]

180 grains will stabilize fine in a 1:11, to say nothing of a 1:10... Hell, Berger's calc says that a 1:10 will stabilize a 200.20 @ 2400 fps. The downsides have already been mentioned. You would be actively hurting your performance with a 1:7. Even if you don't believe that, you're certainly not helping yourself.

 

[st1650]

I wouldn't do 1:7 unless you plan to shoot heavy 220+ subsonics
Actually I wouldn't replace a factory tikka barrel with an IBI to be honest, unless it was utterly shot out.

 

[Chickentoast]

I run 208 eld-m's @ 2640 out of my 11.25 twist. Run fine right to the transonic barrier. Haven't tried further as I have magnums too, but would probably buy a 10 twist if I were rebarreling 308.

 

[308pirate]

I have a 1-7 twist on my 308 and a 14inch barrel. 11.5 gr of TB puts me at 1041 fps with 208 gr. I also get 2407 fps with 44 gr. BLC2 with 168 gr. match. I have a GemTech that I run on it.

But that's a very specialized application (subsonic SBR). 1-7 is not appropriate for general use.

 

[st1650]

I run 208 eld-m's @ 2640 out of my 11.25 twist. Run fine right to the transonic barrier. Haven't tried further as I have magnums too, but would probably buy a 10 twist if I were rebarreling 308.

What’s your powder?

 

[jcmullis2]

I can understand how a person could think this would work. The same thing is done with the 223 all of the time. What the hell give it a try and let us know what happens.

 

[Chickentoast]

What’s your powder?

I have loads for both RL17 and Norma URP. My ho's deep throat allows 3.045 coal still jumping 13 thou to get that velocity without pressure.

 

[THEIS]

Hi,

If you are planning to run monolithics then that twist rate will not do you any harm.

If you are planning on running jacketed projectiles then you will limit yourself to the speed you can push them.

There is a reason the Army has 8 twist in their Barrett MRAD systems.

Sincerely,
Theis

 

[jcmullis2]

I have loads for both RL17 and Norma URP. My ho's deep throat allows 3.045 coal still jumping 13 thou to get that velocity without pressure.

You should call that ho Linda Lovelace. I actually bought my hound dog a t-shirt like Joe Dirt had that says “I choked Linda Lovelace” to wear to the veterinarian when he got fixed. She was a movie star in my best Forrest Gump voice