I know I've seen references to this before, on THF & elswhere, but that nugget of info has disappeared in the fog of gun gack minutia that occupies most of my memory.

My questioning inquiry has more to do with why American Gun Makers almost all use a 9 twist and the Euro's use an 8 twist in 6.5's ...and seem to remember it has to do with what weight bullets shoot best with one or the other twist rate.

100 to 130 gr'ers in an 8, & 125/130 gr'ers up in a 9...or have I got it backwards AGAIN???

I know my SAKO M85 260 has a 8 Twist, as did my now unfortunately departed and no longer available T3 6.5 Swede. Have not spent much time on the SAKO's load ladders...been a little busy getting a bad case of White Coat & Health Insurance Fever with no end in sight .....and concentrating on the proven 120gr SGK's and 130gr NAB's on hand, but the T3 was not easy - aka never achieved anywhere close to the same level of easy consistent accuracy - in 3 brands of C&C 140gr'ers as it did in the lighter bullets mentioned.

Since NIB Swede's are now even more scarce, I'm placing my direction on a 260 or 6.5'06 - with access to brass via other 308 or '06 based rounds - rather than depend on Just One Source. IMO 6.5x284 would be the Best Compromise Do All round but I have not seen any brass in forever anywhere except in Nosler at mega prices higher than Lapua 260's or Swede's.

The Ultimate Goal here is to simplify the Collection & Loading Bench even deeper and eliminate everthing I own...and acquire only One or mebbe Two at most Keeper Grade game shooter calibers and call it good.
Ron

You have it backwards as usually slower twist means heavier bullet. That being said I bet both will work for most hunting bullets.

Incorrect. Heavier bullets require FASTER twist to stabilize properly.

And it isn't weight that's the issue, it's bullet length. It's just that, before the advent of all-copper bullets, generally a longer bullet meant a heavier bullet, so weight was used as a generalization to denote a particular twist rate.

The reason longer bullets require faster twist is because longer bullets tend to have a more rearward center of gravity. This is due to the fact the front portion usually has a longer ogive. The further the bullet's CG deviates from the center of pressure during flight (since the bullet compresses the air as it travels and that center of pressure varies as velocity slows), the faster it needs to spin for gyroscopic stability. Remember the gyroscope or the top you played with as a kid.

Looks like I typed that out wrong o well. Nice catch rifledude.

something else to add to your points on stability is that a slower twist will yield better accuracy within reason if the bullet is stabilized . The faster will typically yield a higher sg but will be less accurate due to jacket thickness variation.

Rifledude got it right. It's actually by bullet length. Most of your 6.5mm shooters and hunting rifles will use the 120 to 130 grain bullets, which need the 9". Only your heavy/long high BC 140 grain bullets need the 8.5" or faster twist. But, a 140 VLD will shoot out of a 9" twist. It's right on the edge, but it should work.

^^Asked and answered^^

Ron, just build a custom with a 1:8.5" twist and it'll run 130's fast or 140's almost fast. That way you have an option. When I was in the 260 business I started with 130's as the barrel got broke in and the brass got a .003" bump on the shoulder they were leaving at 2950 fps.

I switched over to 140's and they shot best at 2800 fps. Lost speed, gained BC, wind holds were the same to 900 yards. I'm married to the 140's and have been for several years. But I could run a 130 if I wanted to for some reason.

Never thought about it...but thank you for enlightening me!

Not to intrude, but is it possible to over stabilize a bullet? It sounds like to me if anyone ever gets an aftermarket barrel to just get a 1 in 8 twist that way it can fire all bullet weights.

Yes. A hard twist and a light bullet will spray them all over the target. The bullet can arrive nose up. Think of a plane land on the runway with the tail hitting first.

Had a fireman come to me with a 243 and a various lot of ammo. I said that twist will shoot the 90 grainers just fine and it will not like the 55 gr bullets. Next shift he came in and said that was exactly what happened.

Twist rate dictates bullet weight (length). They need to work together.

Yes to an extent. It usually isn't a huge problem unless the over stabilization is combined with extra high velocity. Most over stabilized or high sg ranges will retain the highest bc achievable in all conditions elevation being a huge factor but may not shoot the tightest at close range.

Myths die hard.

No, you can't technically "overstabilize" a bullet. What you can do is spin a light jacketed bullet to fast and cause it to fly apart due to excessive centripetal (as opposed to "centrifugal") force. Or, if you spin a poorly balanced bullet too fast, it will amplify its imbalance much like a poorly balanced wheel on your car, and cause poor accuracy.

Just like a spinning football, top, or gyroscope, as an object is spun around its center of mass, the centripetal (as opposed to "centrifugal") forces acting on its circumference becomes equal around its diameter, and the equalized forces cause the object to resist being pushed off course perpendicular to its rotational centerline. This is gyroscopic stability. The more the CG is off center (longer bullet with longer ogive), the faster it must be spun to achieve stability because the further the center of pressure is from the CG, the more the center of pressure acts like a long lever arm trying to push the nose off its rotational axis.

A well-made precision bullet cannot be spun "too fast." Too fast a twist can still shoot a short, light bullet well as long as the bullet in question is built precisely (isn't imbalanced). Too slow a twist, on the other hand, doesn't provide enough gyroscopic stability to a long bullet to keep its nose pointed on the centerline of rotation, especially as velocity slows. Therefore, it is always better to err on the side of too fast a twist than too slow.

The reason the short range benchrest shooters use a slow twist such as 1:14 in their 6PPC rifles is because any faster twist than is necessary to properly stabilize the bullet can cause slight imbalances in the bullet to affect ultimate precision. In addition, it also creates more fouling, they aren't shooting long range, and they're shooting lightly constructed, short bullets.

For LR shooting, using longer high BC bullets, you need faster twist. However, again, as long as you're shooting well balanced bullets, you can still get great precision with light bullets in a fast twist barrel, but the opposite -- long bullets in slow twist -- doesn't work well. A fast twist barrel will shoot a wider range of bullets better than a slow twist barrel. The only reason to select a slow twist in a given caliber is if you're trying to eek out the very best precision possible with short bullets at relatively short range.

The problem is that only a few select companies use good enough jackets to not show an imbalance. J4 being one of the best and only a few use.

Whew...glad I asked that ??? and got out of the way !!!

Explains why Montana Rifle Co's new TAC rifle, when chambered in 6.5x284 is twisted @ 8.5, and all the rest of the regular stock .264 caliber ASR's are twisted as 9's.

After shooting the SAKO & Tikka .264's with an 8 twist, usually in SGK 120 & NAB 130gr'ers, that may explain why the 140gr C&C SP's were picky to get into MOA's and wanted to be driven MO HARD is Mo Bettah, when the lighter bullets were giving me dime sized groups in any powder I tried that was within 2+ gr's of book max. Got most of a partial box of H'dy 140gr RN's that ought to be fun to play with, as they are way shorter than the SP's, and about as long as a 125gr NPT.

Anybody used any of the Lapua .264 Scenar 123'gr'ers, or had good results out of some of the other weights as a Game Bullet?
Hard to fry up paper targets and steel plates...kinda like deer tracks.
Ron

Look up Pat Sinclair (scenarshooter) on 24hr or snipershide as he has killed tons of stuff with the 6.5 Scenar out of various calibers. He posts a bit on 24 in the longrange hunting forum.

Okay Loving this post...But have question?? If my CZ 550 FS is 1:9 I'm not going to find comfort with 140s or 160s? Say inside of 200 meters?

I read Pat's stuff whenever I can find it on the 'Fire, and you are right he's been a good source of Lapua Scenar info...and a very successful Hunter...and where my interest comes from.
Ron

Depends completely on which 140-160 bullets you are talking about. Most average hunting bullets will be fine vld or some monolithic bullets might not be.

I figure if it can handle the elk and large bodied mulie/whitetail up there they would be more than suited for Texas. That being said he seems to be an exceptional rifleman and shot placement will always trump bullet construction.

I dunno Mr Dee...I have had simple brands of SP ammo, slip the core on 3 occasions and found jacket just under the exit side hide(2 hogs and 1 deer) while Nosler Partion hammered all comers and performed well ...for me! Of course this was with a .243 about 15 years ago during one fall season.

Overstabilization I NOT a myth. But, identifying just exactly what it is can be problematic.

A bullet that disintegrates due to excessive rpm out the muzzle is not overstabilized, it is over-revved...two different things all together. Overstabilization is not really an issue for most shooters because its detrimental effects don't become apparent until the range becomes extremely long, as in over 2000 yards or thereabouts.

An overstabilized bullet fired at extreme range will maintain the slight nose-up attitude that was imparted upon it as it left the muzzle. This will cause degraded and changing BC downrange.

An understabilized bullet will likely start tumbling soon after leaving the barrel.

Proper stabilization is a happy medium between insufficient spin and too much spin.

The reason the understabilized bullet tumbles is that the center of pressure is forward of the center of gravity of the bullet in the absence of sufficient gyroscopic force. The further the distance between these two points, the more effect the center of pressure can have on the bullet's attitude and stability. It's about leverage, and that's why a longer bullet requires a faster spin to counteract the center of pressure.

A bullet with too much spin negates practically ALL of the effects of the center of pressure and the result is a bullet that may be pointed above the horizon even though it is in the downward portion of its trajectory.

Think about gyroscopically stabilized artillery shells...these are designed to impact the target nose-first. If overspun, the shell will not nose over but rather maintain an attitude that causes it to bellyflop onto its target (if it even hits it---not likely!). Not only are these shells designed to impact nose first (the fuse is on the nose) for proper detonation, but a bullet flying in such a way would have a changing BC that would make it impractically difficult to predict just where it's going to hit.

A properly stabilized bullet tries to become unstable due to the center of pressure exerting force upon it, but as soon as that force is applied to one side of the nose of the bullet, gyroscopic force makes the bullet's nose move in a direction 90 degrees away from the force applied by the center of pressure. Then as soon as this has happened, the center of pressure has changed position on the nose of the bullet, which is again---and constantly---trying to catch up to the movements caused by gyroscopic force. So as the bullet flies down range, the center of force is chasing the effects of the gyroscopic force in futility. It's like a game of keep-away.

When a bullet is overstabilized, the center of pressure has little to no effect on the attitude of the bullet because the gyroscopic force is too great.

So...overstabilization is a real phenomenon, but it just is not a factor for most of us. When the world record longest confirmed sniper kill came in about a year ago, I did some math on the whole thing and concluded that that bullet would have had about a 16-degree (IIRC) nose-up attitude at impact if it had been overstabilized. That may not sound like much, but I'll bet it would have made hitting the target at that range impossible due to degraded BC and an unpredictable trajectory.

Mmmm...I left out a major point: when the nose of the bullet is doing its wobble-thing with the center of pressure chasing the gyroscopic movement round and round the nose of the properly stabilized bullet in flight, the nose of the bullet is kept forward and the bullet's axis of spin is maintained to be tangent to the arc of trajectory because the effects of the center of pressure are not entirely negated. The bullet can be fired at long range with an elevated muzzle, but the bullet will still impact the target nose-first, and optimal BC is maintained throughout the bullet's flight.

^^Good stuff^^ And just trying to help explain:

A gyroscopically stable bullet with a dab of ink on the tip would leave a dot on a target if we could stop it, one that is not would draw a circle.

JG, I know you shoot steel at extreme ranges so it would be difficult to tell...but if you shoot paper a properly stabilized bullet will leave a perfectly round hole. If a bullet is insufficiently stabilized it will tumble and make all kinds of interesting holes in the target (been there). But if you ever see evidence of the bullet hitting the paper nose-up consistently, you've got an overstabilization issue (never been there and have no plans to visit).

I was referring to when a bullet goes subsonic and looses gyroscopic stability. Thus drawing the circle while still in flight. I wasn't clear.

It is on my mind today since a friend and I have a 338 LM project we're going to push to 2000 yards. I had to investigate about where it goes transonic. But at "reasonable" ranges I know you are correct.