Speed == Stability

The website says it wants a 1:9 twist but that's assuming its coming out of a 223. I emailed customer service and they said it might work out of 1:10 because of the extra speed out of a 22-250 vs 223.

Sure enough, they are #1 sexy time.

I got some Sierra 90gr bullets (#9290T) and my rifle is far from the 6.5" twist noted on the box. As indicated above, I've found if I push the bullet fast enough the rotations cause it to stabilize even if it's not the documented required twist rate.

I sent an email to sierra which includes this info and basically asks: What is the RPM or RPS required to stabilize item number 9290T 90gr bullet?

Even better, does anyone else think it would be of value to have manufactures document the recommended twist rate but also the required RPM/RPS to stabilize the bullet? They are already doing it w/ the twist rates anyway, are they not?

Maybe. The thing is it’ll lose stability at longer range. I am pretty sure recommended twist rates are assuming it maintains gyroscopic stability down to around trans sonic speeds.

Pushing things faster only gains a modest amount of stability. So if it was unstable and inaccurate at 2400fps, but fine at 2600...guess what is going to happen as it dips towards 2400?

It is partly why if you’ll ever shoot long range, you want to test load accuracy at medium and long range also. Just because it stabilizes and is super accurate at 100yds, doesn’t mean as it slows passing 300 it doesn’t start to become disturbed in flight and loses accuracy.

Just a thought about it.

lazarus said:

Maybe. The thing is it’ll lose stability at longer range. I am pretty sure recommended twist rates are assuming it maintains gyroscopic stability down to around trans sonic speeds.

Pushing things faster only gains a modest amount of stability. So if it was unstable and inaccurate at 2400fps, but fine at 2600...guess what is going to happen as it dips towards 2400?

It is partly why if you’ll ever shoot long range, you want to test load accuracy at medium and long range also. Just because it stabilizes and is super accurate at 100yds, doesn’t mean as it slows passing 300 it doesn’t start to become disturbed in flight and loses accuracy.

Just a thought about it.

Click to expand...

In my mind this doesn't make sense, so help me out a bit. If you start off with a higher initial velocity out of a given twist rate, the twist RPMs should be higher because it's rotating the same amount in less time. Now as the bullet travels, its velocity will reduce as it encounters wind resistance.... but how much does the spin actually reduce? I'd think the RPMs would have less drag than the forward motion through the air. So by the time it falls to 2400, it would essentially have the equivalent spin as it would out of a faster twist barrel if the muzzle velocity was 2400. I dunno. I'm probably way off here though.

Moorvogi said:

The website says it wants a 1:9 twist but that's assuming its coming out of a 223. I emailed customer service and they said it might work out of 1:10 because of the extra speed out of a 22-250 vs 223.

Sure enough, they are #1 sexy time.

I got some Sierra 90gr bullets (#9290T) and my rifle is far from the 6.5" twist noted on the box. As indicated above, I've found if I push the bullet fast enough the rotations cause it to stabilize even if it's not the documented required twist rate.

I sent an email to sierra which includes this info and basically asks: What is the RPM or RPS required to stabilize item number 9290T 90gr bullet?

Even better, does anyone else think it would be of value to have manufactures document the recommended twist rate but also the required RPM/RPS to stabilize the bullet? They are already doing it w/ the twist rates anyway, are they not?

Click to expand...

No because when the density of a bullet is less than lead or the density of the resisting medium is greater than air the spin should be increased as the square root of the ratio of the two densities.
Unless of course the bullet was to be fired in a heavier medium such as water which would require the spin to be increased approximately four fold for it to be stable.
What your describing is the problem known to Bashforth regarding rotational shear in naval shells which was later taken up by Greenhill who later surpassed him at Woolwich and was original based off early observations in 1746 by Benjamin Robbins and just prior to him by a Capt Cundhill.
Its called the rate of diminution of spin and involves complicated mathematical
formulas outside my realm of expertise or ability to effectively express in an MDS post.
But I know where to get the answer and that's what counts

Lazarus is right on track because there are influences that occur as parallelism of trajectory changes due to velocity and distance traveled are combined with gyroscopic effects enacted by internal mass and densities of the projectile composition and mechanical effects placed on bullet envelope material(s)
The initial problem was trying to keep ordnance from self destructing naval gunnery from being at rest and then being abruptly placed into motion.
It was the gun barrel that was being sheared and twisted rather than the shell.
Eventually the engineering made it way into small arms development as bullets of streamlined shapes became prevalent allowing everybody to put bullets in one hole with a 300 dollar rifle and little to no effort of the users behalf.

And to be clear as mud, faster will generally make things more stable. But there is less to be gained there than just having a faster twist from the barrel.

IMHO I know you can get custom barrels made, but my annoyance that some things have never bother being updated. Like .22-250 would be nice to move down towards 1:7-1:8 being more standard. Probably not going to spin a 40gr varmint round so fast it disintegrates. Would help a ton in stabilizing very long bullets.

Also my annoyance with all of the .223 bolt gun manufacturers that STILL make 1:9 barrels. Sure, don’t need to worry much about stabilizing a 62gr tracer, but it would sure be nice to make a 77gr or even 85gr nice and stable

Moorvogi said:

The website says it wants a 1:9 twist but that's assuming its coming out of a 223. I emailed customer service and they said it might work out of 1:10 because of the extra speed out of a 22-250 vs 223.

Sure enough, they are #1 sexy time.

I got some Sierra 90gr bullets (#9290T) and my rifle is far from the 6.5" twist noted on the box. As indicated above, I've found if I push the bullet fast enough the rotations cause it to stabilize even if it's not the documented required twist rate.

I sent an email to sierra which includes this info and basically asks: What is the RPM or RPS required to stabilize item number 9290T 90gr bullet?

Even better, does anyone else think it would be of value to have manufactures document the recommended twist rate but also the required RPM/RPS to stabilize the bullet? They are already doing it w/ the twist rates anyway, are they not?

Click to expand...

Go read some of Bryan Liz stuff, I think your ready....

However... "the website", who's?

It should be noted velocity, not an assumption of cartridge. Barrel length matters, (BLM) does it not?

Stability is a relative factor. You can be stable but shedding BC to the point a lower drag curve bullet might be better, because its faster. Look at Berger's site. Berger does your last question.

You’re right laz, makers should have gone to a 7 twist yrs ago. I remember vaporizing some 40 gr hornet bullets in a 220 swift many years ago. Vapor trail ended at about 75 yds and nothing ever got to the target. Don’t recall the speed but it was well over 4000

The short answer is that RPMs decay much more slowly than Velocity . So yes , in the combination of long ( generally heavier) bullets with marginal on the slow side twist rates . more speed helps .

Because changing handloads is easier and less expensive than re barelling .

*************************

Notwithstanding Texas deer hunters , the traditional , and originally intended purpose of .22-250 is Varmint Hunting . The typical contex is flat trajectory , to hit prairie dogs and ground hogs at unknown distance , out to 500-ish yards . For that , 50- 55gr bullets going really fast is the goal .

That's why the traditional twist rate is 1 : 14 . 1:10 is already Fast Twist for a factory .2 2- 250 .

lazarus said:

Also my annoyance with all of the .223 bolt gun manufacturers that STILL make 1:9 barrels. Sure, don’t need to worry much about stabilizing a 62gr tracer, but it would sure be nice to make a 77gr or even 85gr nice and stable

Click to expand...

224 Valkyrie
The 90gr. SMK "requirement" for a 6.5-7T barrel is based on the AR-15 based 224V cartridge, which is likely one of the few applications for this bullet. Sierra provides 90SMK's to Federal for their 224V ammo.

Rps decays so much more slowly than velocity the bullet would have to fly for lke a quarter of an hour to have any real effect that can be detected.
If one were to attempt the control bullet yaw and instability the answer I think would be to buy the best bullets one could find and start there.
The real answer lies to where the bullet has not even started moving and it is of near perfect concentricity it could be.
I would simply ask the bullet manufacturer to provide information regarding the relationship between the bullet core and the exterior or envelope material
or start looking into all copper bullets or bullets made entirely of the same materials.

You can figure out the RPM.

You know the minimum recommended twist rate for that bullet in an AR. You know what the muzzle velocity is for that bullet in an AR.

MV x (12/twist rate in inches) x 60 = Bullet RPM

So 1 in 8 with 2600 fps = 23,400 rpm