.308 9 tw

[6BRinNZ]

Is anyone playing with a 9 tw for .308? This would be to completely stabilise some of the new looong bullets coming out in the 200 grn class.

In general does going to a faster twist have a significant affect to precision? i.e. for FTR from a 1/10 - 1/9

I appreciate that a faster twist is counter intuitive to precision but what are the experiences of the actual impact (%) to groups?

Can the long high BC bullets in 200 grn .308 be taken advantage of or is the extra twist needed to fully stabilise trading off significantly reduced precision?

 

[Down South]

The current barrel i'm shooting Berger 200.20X bullets in is a 30 inch HV contour Bartlein 5R 9 twist barrel. I orginally bought the barrel to shoot other longer bullets in but that didn't work out so I tested the X bullet in it and it shoots really well with them. I've shot several 1000 yard matches in FTR with it this year and it shoots just as good as my 10 & 11 twist barrels. I don't see any difference accuracy wise and i'm running the same speed as I run with the slower twist barrels. With that being said, I wouldn't buy a 9 twist barrel specifically for the X bullet as I don't think it's necessary to spin that particular bullet that fast but it doesn't seem to be hurting anything in my experience. If you are thinking about other 200 gr bullets that are longer than the X bullet then I would definitely get the 9 twist barrel.

 

[dcali]

The difference in accuracy is roughly proportional to change in twist. It's small but real in an F class context.

 

[6BRinNZ]

The current barrel i'm shooting Berger 200.20X bullets in is a 30 inch HV contour Bartlein 5R 9 twist barrel. I orginally bought the barrel to shoot other longer bullets in but that didn't work out so I tested the X bullet in it and it shoots really well with them. I've shot several 1000 yard matches in FTR with it this year and it shoots just as good as my 10 & 11 twist barrels. I don't see any difference accuracy wise and i'm running the same speed as I run with the slower twist barrels. With that being said, I wouldn't buy a 9 twist barrel specifically for the X bullet as I don't think it's necessary to spin that particular bullet that fast but it doesn't seem to be hurting anything in my experience. If you are thinking about other 200 gr bullets that are longer than the X bullet then I would definitely get the 9 twist barrel.

Thanks - yeah this is for the longer 200 grn bullets that show as marginally stabilised in a 10tw and fully stabilised in a 9tw. All of my tricks that would normally have a Berger dialed in still only have me sitting on 3/4 moa. The difference must be more than just twist. I've reached out to a few shooting these bullets and all I have come across are still using a 10tw with very good results. I wanted to try and use the full BC potential of the bullet and needed a new barrel so went with a 9tw.
Good to know on the 200.20 in a 9tw thanks.

@damoncali - thank you.

 

[Ned Ludd]

I just started shooting a 30" 9-twist barrel earlier this summer in a new .308 Win F-TR rifle. If there is any difference in precision as compared to the 10- or 11-twist barrels I already have, I can't shoot the difference. I went that route for the same reason as you; the ability to shoot some of the newer and longer 200 gr .30 cal bullets available where you can't net the full BC with a 10-twist. Ideally, I would have gone with a 9.5-twist. However, it's not too hard to find a supplier with 9.0-twist barrels in stock; a 9.5-twist will almost certainly have to be ordered direct from the manufacturer with a concomitant increase in lead time.

In theory, there can certainly be issues that seem worthy of special attention, such as not using a barrel twist rate that is ridiculously faster than it needs to be. In actuality, it may not be so easy to tell the difference, depending on the type of shooting you do. I have .30 cal barrels ranging from as fast as 8-twist to 12-twist. They have all shot with very good results in terms of precision. The faster twist rate may increase torque on the rifle, and it may affect precision in some small way, but for a shooting discipline such as F-TR, if the change isn't sufficient to become the limiting factor, you'll never notice it. Things that might easily be a deal breaker in short range BR won't necessarily kill you in F-TR, where wind calls are most often going to be the limiting factor.

 

[Crosshair1]

I've been having a play around with a 9 twist bartlein 5r 308 28", mainly for fun though.

Its got a 0.170 freebore which is not ideal for the heavies or for that matter the lighter either.
Ive ran 155amax, 168vld, 168tmk 175smk, 185jugs, 200 & 230new smk, 215 hybrids in it, and to be honest I dont feel I could tell a difference between it and my 10tw barrel.

The 155amax and 175 smk were ran at mag length, the 215s are just above donut area, 230s are just in it.
The main issue I believe is that to maximize the benefits of the twist rate at long range, requires that the is throat pushed way out and no longer suited to the lighter bullets - so you better not have a problem shooting heavies .

My mid range load is a 215hybrid at a little over 2400fps, makes for a soft recoiling 17lb gun.
Ive just started having a play with the 230smk's and they are showing promise in the 2400fps region also.

 

[6BRinNZ]

Thanks guys. I have the 200.20 holding .4moa at 1000 ftr in a 10tw. Same for 185s in another barrel so I'm all good with this weight of bullet.
These new long 200s n a 9 tw I haven't been able to get under 3/4 moa at 100 so I'm not going to take them further out yet.
Reamer spec fb is specific for this bullet.
The powder and seating depth I landed at so far aligns with others in 10 tw.
However I'm hearing the twist probably isn't the issue.

 

[Down South]

Thanks - yeah this is for the longer 200 grn bullets that show as marginally stabilised in a 10tw and fully stabilised in a 9tw. All of my tricks that would normally have a Berger dialed in still only have me sitting on 3/4 moa. The difference must be more than just twist. I've reached out to a few shooting these bullets and all I have come across are still using a 10tw with very good results. I wanted to try and use the full BC potential of the bullet and needed a new barrel so went with a 9tw.
Good to know on the 200.20 in a 9tw thanks.

@damoncali - thank you.

Not sure what other bullets you're trying but like I mentioned in the post above, it seems to shoot the X bullet well in my setup. Earlier this year at 1000 yard two day match I shot 200-8X on the 1st string of the 2nd day of the match so it's definitely not hurting accuracy that I can tell.

 

[6BRinNZ]

Not sure what other bullets you're trying but like I mentioned in the post above, it seems to shoot the X bullet well in my setup. Earlier this year at 1000 yard two day match I shot 200-8X on the 1st string of the 2nd day of the match so it's definitely not hurting accuracy that I can tell.

Thanks. I'll put a line under the twist and say less likely to be the issue. I'll keep playing as I can fall back to the x which is working in another barrel.