if a bullet stabilizes at a 100

[B.W.]

So I have 223 bolt action 1&9 twist and it shoots the 69 and 70gr bullets great. I just got a good deal on some 75gr hornady hpbt, I've been wanting to try something a little heavier to see if my gun would stabilize them. So I loaded up some test loads and went to the range today. I shot 3 shot groups at a hundred yards with various powder charges. Out of the 8 groups the avg. was little under 3/4". So if these seem stable and fairly accurate at a hundred are they good to go at longer ranges?

 

[Lj1941]

I am not a ballistics expert -but I would think you would be good to go at longer ranges.Just my opinion.:banghead:

 

[Jim K]

A rifle bullet will stabilize at well under 50 feet if it is going to stabilize at all. Under that, you can get keyholing and instability even with bullets that eventually settle down.

Jim

 

[morcey2]

A bullet is at its least stable right out of the barrel (and muzzle blast) until it hits the trans-sonic region which will also cause it to destablilize. If it's stable at 100 yards, it will remain stable out until it drops to the 1000 fps or somewhere in there. Or until it hits something.

Matt

 

[B.W.]

Thank you

 

[hartcreek]

Maybe ....It could well be that the 200m could be at the transonic distance and it could well become unstable. You will just have to try it and find out.

 

[243winxb]

Compare the length of your 3 bullets, it may tell you something. Its the length of the bullet, not the weight that counts. Long bullets need faster twists. Old but interesting link. http://www.6mmbr.com/223rem.html

 

[Jim Watson]

Empiricism is everything.
If they shoot well at 100 yards they will likely hold up to longer range.
A friend's 9 twist Hart barrel will also stabilize the 75 and shoot it reasonably accurately with less wind drift. But the 69 is more accurate in a calm. Decisions, decisions.

Shoot the gun.

 

[USSR]

I will respectfully disagree with the assertion that a bullet that appears to be stable at 100 yards, will be stable at a greater distance. In F Class competition I was shooting with a guy whose load was stable at 600 yards, but not at 1,000 yards. This was a heavy bullet load in a .308 Winchester. A bullet can be marginally stable at close range and come undone at greater range.

Don

 

[Nickb45]

Like someone said above once it drops below a certain speed it will not be stable any longer.
It would really depend on the load used and how long it will stay stable.

 

[Walkalong]

It will continue to be stable until it loses enough velocity/spin to stabilize. Where that is depends on muzzle velocity, bullet shape etc.

 

[pseudonymity]

I will respectfully disagree with the assertion that a bullet that appears to be stable at 100 yards, will be stable at a greater distance. In F Class competition I was shooting with a guy whose load was stable at 600 yards, but not at 1,000 yards. This was a heavy bullet load in a .308 Winchester. A bullet can be marginally stable at close range and come undone at greater range.

Don

That is true, but the destabilization once the bullet is trans-sonic is for a bit of a different reason AFAIK. Spin on the bullet helps stabilize the bullet against pressure differentials around the bullet in flight. If the bullet leaves the muzzle when the center axis is not exactly in line with the bore, pressure is not the same all around the bullet (kind of like air over the wing of a plane). Spin counters that force.

As the bullet slows into the trans-sonic region, the center of pressure moves relative to the center of mass of the bullet and that can cause the bullet to destabilize. This is due to pressure also, but pressure applied more or less equally around the bullet, not more on one side than another.

 

[pseudonymity]

Compare the length of your 3 bullets, it may tell you something. Its the length of the bullet, not the weight that counts. Long bullets need faster twists.

I am pretty sure that is not the case. It does not usually matter to us, since bullets are generally all constructed with a lead core and copper alloy jacket, so longer bullets also have more mass.

Two bullets of the same shape and volume but constructed of aluminum and tungsten would require different amounts of spin to stabilize. Even the Greenhill formula for spin rate uses specific gravity as a variable, but since the formula is normalized for lead core bullets it gets left out.

 

[USSR]

...destabilization once the bullet is trans-sonic is for a bit of a different reason AFAIK.

Only problem is, this was a Berger bullet with a BC of .631 and was not transonic at 1k.

Don

 

[Walkalong]

I am pretty sure that is not the case. It does not usually matter to us, since bullets are generally all constructed with a lead core and copper alloy jacket, so longer bullets also have more mass.

Two bullets of the same shape and volume but constructed of aluminum and tungsten would require different amounts of spin to stabilize. Even the Greenhill formula for spin rate uses specific gravity as a variable, but since the formula is normalized for lead core bullets it gets left out.

We usually talk about bullet weights vs twist rate but it is the length that matters, so yes, a bullet constructed of something lighter than lead bullet will require a faster twist for bullets of the same weight, because it will be longer.

Its the length of the bullet, not the weight that counts. Long bullets need faster twists.

That's correct.

 

[HJ857]

You can use this calculator to run numbers to determine theoretical stability as a good starting point. I'd stil test them though. There's also a possibility that your rifle will stabilize them but not shoot them well at all.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi