Velocity and twist vs. bullet weight and type

[rig_pig69]

So I'm not 100% sure where to ask this, but seeing as precision is the name of the game, I'll try here first.

I'm in the middle of building a new rifle, a lazer beam if you will, for coyotes.
I'm curious though if there is a general 'rule' on the limits of twist and velocity on bullets.
For example... if one was to push an 6mm, 80gr tipped TSX at say....4000fps, through a 1:9 twist, would it come apart, tumble, or fly true as true can be??
Also, which bullets are better suited for high speeds?

Thanks.

 

[nate18]

the faster the twist the heavier the bullet. i think boat tailed would be best for speed but good luck for 4000fps. can anybody say thev'e gotten 400 fps with an intact bullet hitting the target?

 

[Obtunded]

the faster the twist the heavier the bullet. i think boat tailed would be best for speed but good luck for 4000fps. can anybody say thev'e gotten 400 fps with an intact bullet hitting the target?

LENGTH of bullet determines the requirment for twist, not the bullet weight. Formulas like the Greenhill Formula don't even factor bullet weight into them.

Here is a utility that helps. Pick up Brian Litz's book and read on the subject in greater detail abour bullet stabilization.

It is perfectly possible to achieve excellent accuracy with fast bullets, if the bullets are stable at that speed. Frankly, i wish bullet manufacturers would specify the range of RPM required to stabilize a bullet because twist rate produce wildly different RPMS depending on how fast a bullet is travelling.

A 300 whisper and a 300-338 Lapua propel bullets at very different speeds. No one twist rate will properly apply.

 

[Glock4ever]

Twist rate is only one factor in stabilizing a bullet, you also have jacket thickness, bullet length (i.e. Barnes bullets of equal weight tend to be longer so some require a faster twist barrel), velocity, etc. To answer your question, I don't think a TSX can come apart it is a monolithic bullet so they tend not to break apart at high RPM's compared to jacketed bullets. It should shoot pretty well out of a 6mm 1:9 twist barrel. I don't even know how to answer your last question as it is unclear as to whether you are referring to the ballistic performance (do you want it to stay supersonic for a specific distance?)/terminal performace (do you want it to kill well?)/accuracy (does it need to shoot itty bitty holes?). Bullets good at one may not necessarily be good at the others.

 

[Barks]

You'll need a BIG case full of powder. My .243 out of a 26 inch barrel using 55gr Nosler Ballistic tips made 4028 as an average for 5 shots. This was a max load of Varget to get there. I don't know what you'll be using to push 6mm 80grainers to those velocities.

Generally the 8 twist should get you stability for all bullets in the 6mm weight range for varminting. some bullets will come apart with the 1:7 and faster twists.

 

[roberti11]

You have had good input on others as far as twist rate, and stabalization so I will bring up another point, Why do you want to go that fast? I would estimate that a 6mm bullet at 4000 rpm will eat the throat within the first 500 rounds, you may build yourself a laser but you will be giving replacing barrels and spending $$ almost as fast as your bullets will fly

 

[rig_pig69]

You'll need a BIG case full of powder. My .243 out of a 26 inch barrel using 55gr Nosler Ballistic tips made 4028 as an average for 5 shots. This was a max load of Varget to get there. I don't know what you'll be using to push 6mm 80grainers to those velocities.

Generally the 8 twist should get you stability for all bullets in the 6mm weight range for varminting. some bullets will come apart with the 1:7 and faster twists.

The rifle I've picked for this project is a Rem 700, and is chambered 6-06 AI, with a 26" barrel.

 

[rig_pig69]

You have had good input on others as far as twist rate, and stabalization so I will bring up another point, Why do you want to go that fast? I would estimate that a 6mm bullet at 4000 rpm will eat the throat within the first 500 rounds, you may build yourself a laser but you will be giving replacing barrels and spending $$ almost as fast as your bullets will fly

Why so fast?? Why not?? I really wished i had a valid reason other then just because.
And yes, I am aware of the life expectancy, and am willing to risk that in exchange for having something a little different from the rest.