Rate of twist

[Gater]

Why does Bartline make .223 barrels with twist rates so close to one another 1-7.7
1-7.5 and 1-7 ? Just curious I am getting ready to replace my Bartline going from
1.7.7 to 1-6

 

[Medic505]

Personal preference? I choot 90 vld's out of a 1-6.7 and some will say that's more than needed. 1-6 is pretty fast, what bullet are you going to shoot?

 

[Gater]

Personal preference? I choot 90 vld's out of a 1-6.7 and some will say that's more than needed. 1-6 is pretty fast, what bullet are you going to shoot?

Berger 80.5 85.5 and 90s

 

[Medic505]

IMHO, I don't think you need a 6 twist for any of those bullets. Jump in here .223 guys, I may be wrong. It is possible to over spin a bullet.

 

[Gater]

IMHO, I don't think you need a 6 twist for any of those bullets. Jump in here .223 guys, I may be wrong. It is possible to over spin a bullet.

I spoke with Bob from Berger about the new 85.5 he told me that the 85.5s would stabilize but with a faster twist I would get better performance to shoot the 90s I would need a 1-7 to get max performance I could get away with a 1-7 no problem the loads he gave me for the 85.5 where fired from a 1-6 that he was shooting at 1000 yds which is asking a lot for a .223

 

[Ned Ludd]

There is currently not a single .224" bullet made that requires a 6-twist for full stability. All you're doing by running a twist rate that fast is to increase the risk of shedding a jacket. It will not improve performance whatsoever. That is not to say you can't occasionally get away with using a faster-than-necessary twist rate...you can. But take it from someone that has used a .223 Rem in competition for many years and has had jacket failures due to an excessively fast twist barrel - .224" bullets are not the place to experiment with much faster-than-necessary twist rates; they don't like that. Use the minimum twist rate necessary and no more. In this case, a 7-twist will do everything you need it to do (Edited to add - that includes the 90 VLDs).

 

[Jdne5b]

PS (And Medic too)

PPS (I have a 1-6 and I still agree with them)

 

[Dusty Stevens]

Oh yall got 1:6? Yall done caught up with me, i just ordered a 1:5 and a 1:3.75 just incase yall catch up before i get that 1:5 shooting. Now i just need somebody to make a 157gr bullet.

 

[Gater]

There is currently not a single .224" bullet made that requires a 6-twist for full stability. All you're doing by running a twist rate that fast is to increase the risk of shedding a jacket. It will not improve performance whatsoever. That is not to say you can't occasionally get away with using a faster-than-necessary twist rate...you can. But take it from someone that has used a .223 Rem in competition for many years and has had jacket failures due to an excessively fast twist barrel - .224" bullets are not the place to experiment with much faster-than-necessary twist rates; they don't like that. Use the minimum twist rate necessary and no more. In this case, a 7-twist will do everything you need it to do (Edited to add - that includes the 90 VLDs).

I have also been shooting a .223 for many years over 30 and a 1-7 was all we needed for a long time my only real question was will a 1-6 help stabilize the heavy bullets better the 1-7 will shoot the 90s but will the faster twist shoot better and it sounds like it won’t so instead of paying the extra for a special order I’ll just get the Bartline 1-7 28” thanks for the input hope all have a good Holiday and keep shooting

 

[geo.ulrich]

Oh yall got 1:6? Yall done caught up with me, i just ordered a 1:5 and a 1:3.75 just incase yall catch up before i get that 1:5 shooting. Now i just need somebody to make a 157gr bullet.

you could draw down a 1.500 30

 

[ebb]

Well I hate to tell you all what my next project is. It's a 30 BR with a 7 twist. So I wanted to build a suppressed rifle and already had an action with a .473 bolt face. So 300BLK was out and I thought the smallest case I could do was a 30BR. So 30 br 7 twist 220 SMK at 1050 fps???? I am reading 8 twist is some times not fast enough.

 

[Ned Ludd]

I have also been shooting a .223 for many years over 30 and a 1-7 was all we needed for a long time my only real question was will a 1-6 help stabilize the heavy bullets better the 1-7 will shoot the 90s but will the faster twist shoot better and it sounds like it won’t so instead of paying the extra for a special order I’ll just get the Bartline 1-7 28” thanks for the input hope all have a good Holiday and keep shooting

There is potentially more than simply the barrel twist rate involved in the issue of maintaining jacket integrity. According to Berger's Twist Rate Stability Calculator (https://bergerbullets.com/twist-rate-calculator/), a 90 VLD at ~2850 fps and generic atmospheric conditions (1000 ft elev., 65 degrees F) will not quite reach a gyroscopic stability coefficient (Sg) of 1.5 and therefore be giving up a small amount of its intrinsic BC (~2%). For that reason, I special-ordered 6.8-twist 5R barrels from Bartlein for my last .223 Rem F-TR build; just to make sure "everything" was optimized for the 90 VLDs.

Certainly, a 6.8-twist may not seem sufficiently faster than a 7.0-twist to cause problems, but at 2850 fps the calculated bullet RPM goes from 293K to 302K. According to Berger, if you're spinning the 90s at over 300K RPM, all bets on the jackets retaining integrity are off. I started losing bullets not long into the new rifle with the 6.8-twist barrel, something I've never once experienced with a 7.0-twist barrel. When something like that happens during a match in which you were otherwise doing pretty well, it's even worse and can create confidence issues with the brand new rifle, also not desirable.

There are isolated examples where markedly over-spinning a bullet such as the 168 Sierra Matchking, which has a very steep boattail angle that causes dynamic instability past about 700 yd or so, can actually keep it stable a little bit further and help minimize or prevent tumbling/keyholing and improve precision at longer distances. However, it is not generally necessary to over-spin bullets, and does not typically provide any obvious benefit such as improved long range precision, etc. In a case such as the .223 Rem with heavies where we tend to push the loads very hard, and we know jacket failures are a possibility, using a twist rate sufficient to retain most of the intrinsic BC without grossly over-spinning the bullet is one way to help minimize the chance of a jacket failure.

However, there are certainly other ways to accomplish the same goal. For example, it is likely that most, if not all, jacket failures originate as a result of friction and heat at or near the point of contact between a rifling land and the bearing surface of the bullet. Frank G. from Bartlein has suggested it may be a better idea to use a 0.219"/0.224" barrel configuration, rather than a 0.218"/0.224". The implication is that the tighter bore increases friction and the potential for jacket problems, regardless of the twist rate. Certain types/shapes of rifling are likely to be harder on the jackets than others. The point being that there are likely a number of factors that go into jacket failure, and it is equally likely that some combination of unfavorable events (and not necessarily the same events in every situation) is necessary to cause a jacket to let go. In my case, I have the 0.218"/0/224" (tighter) bore/groove configuration, as well as the slightly faster 6.8-twist. It is certainly possible, even likely, that the combination of those two features is the primary contributor to jacket failure. However, I can never rule out with 100% certainty that something else may wrong with that particular barrel. I have bore-scoped it three ways from Sunday and cannot see anything out of the ordinary, but I will likely never know what the problem is with any certainty.

I attached a readout from Berger's Twist Rate Stability Calculator for both the 90 VLD and the 85.5 from a7.0-twist barrel under fairly typical conditions, using what should be very close to optimally "tuned" velocities for each. As you can see, the 90 VLD does not quite achieve the full intrinsic BC out of the 7-twist, but it very close. The shorter and slightly faster 85.5 has an Sg well above 1.5, and there should not be a good reason to spin those any faster.