How fast, and what weight, must a bullet run to stabilize in a 6 mm , 14 twist barrel?

[woodnut]

Well, I leaped before I looked. I had a barrel rechambered before we knew the twist rate. Thought it was going to be either a 10 or 12 twist; but turned out to be a 14 ! I sure could use some input about what to run and how fast to stabilize it. My thoughts are 55 gr. at sizzling speed, or max out at 70 gr? Your thoughts?

 

[Dmagna]

use the Berger stability calculator

 

[GLTaylor]

Above. It's going to be light and fast!

 

[woodnut]

So, I think according to the Berger chart, I may get away with a 70 gr. stability better than a 55gr. But I gotta drive it about 3400! I think I may get there, but it's gonna need a lot o luck! Thanks guys, I really appreciate your help!

 

[cape cove]

There seems to be a good deal of 6mm PPC and 6mm br Norma's out there that use 14 twist barrels and use 55-68 gr bullets with great accuracy. The lighter bullets will stabilize more than the higher ones. Velocity has some impact on stability but not a great deal. Use the Berger twist calculator and plug in different velocities and you will see the effect it has. Bullet length has a much greater deal to do with stability.

 

[woodnut]

Would you say shorter is better?

 

[cape cove]

Not in all cases but most often a lighter bullet is shorter than a heavier one. Bullet length is the #1 ( IMO) factor in bullet stability although flat base bullets react differently than do boat tail ones. You could use slightly longer ones than boat tail ones and get good stability. Berger lists the required twist on their boxes. Depending on your accuracy requirements you will have to use a bullet of proper length to achieve your goals .

 

[woodnut]

Thank you cape cove. I have made a blunder by not verifying the twist rate b4 a re-chamber job. I pretty much thought it would be 10 or even 12 twist; but it came up at 14. I have some very nice flat base 70s I'm gonna try to see how they do. Chrono them and see how they run and hit the paper. Wish me good luck!
I looked up 6 BR and 6 Rem and 243. looking at case capacity and attending vel. gives me hope for my 6 Creedmoor.

 

[Dmagna]

Use varget, N540, for the smaller bullets. You can also try the normal stuff like H4350 or RL16. But with the lighter bullets you might have better luck with the faster powders with the lighter bullets.

 

[woodnut]

Thanks again,Magna, and I think I have some of those powders. Will hopefully get it sighted in with something so I can run some over the chrono. It may take a bit, but I'm confident it will find a load.

 

[30BR]

I think this is about the biggest you'll get... From BIB Bullets...
6mm – 67.0 Gr. FB, BC – .28. Made in Niemi carbide dies, 8.5 ogive/.055 meplat, .2435 pressure ring; .2433 shank: use 1:14″ or, faster twist; ideal twist for the 67 Gr. FB is 1:13″. $288.00 per 1,000.

 

[shinbone]

I played around trying to stabilize marginally stable bullets by shooting them faster. The increased speed didn't seem to help. I think what is happening is; as the bullet is made more stable by spinning faster, the de-stabilizing force of the air pushing on its nose increases, too, due to the increased speed. One force off-sets the other, and there is no net stability gain. Accordingly, increased speed won't improve stability. At least that's how I think of it.

Your only two options are a faster twist or a shorter bullet. Obviously, once you've chosen a barrel, the only variable left is bullet length. Note that for a given weight, a flat base bullet will be shorter than a boattail bullet.

 

[Randy Tidwell]

14 twist is the go to for 99% of the BR shooters. Majority shoot 65 to 68 grain pills. Running around 3100 to 3200.

My favorite PD gun is a 6PPC with a 14 twist shooting 70 Sierras, deadly on dogs out 400 with no wind. Hard hitting combo.

 

[woodnut]

Great intel, guys, and once again, THANK YOU VERY MUCH for it! I do think shinbone is right, speed and air negate anything with the bullet wt.,shape. I do have some 68 gr and some 70s that are flat based to see if I can make them work. It may take a while, but I believe there is a workable powder combo/speed. I like Randy's speed of no more than 3200 to save wear on the barrel and whack P.D.s out to 400! I'm heading to S.D. this June to do just that!