How did it fail? You put a c&c bullet in the boiler room and the animal was dispatched.

The trans-sonic phenomenon is something I've never really looked at. I spent lots of time looking at the reason a well stabilized bullet flies as it does and it took a while to wrap my head around it. My curiosity is exhausted for now. But since it's on the table, care to offer some insight on it?

Couple things I've seen.

Load a 168 SMK in a 308 Win and take a poke at 1000 yards. When the lighting, wind, and mirage is right you can watch trace, about 900 yards, give or take, no more trace, it went subsonic. Load a 175 SMK and it'll still be supersonic to 1000 and a bit beyond. Higher BC is all that is.

Some bullets will handle trans-sonic better than others. Really high BC seem to do a bit better. Take my 180 VLD out of my 7 Rem Mag. Really high BC and its leaving the muzzle fast (barrel burning fast). I took a poke at a mile with it. Ballistic calculator said I'd lose the speed of sound at 1650-ish in the current environmentals. It made it to the 1760 mark after about 7 tries. But once I got my elevation and windage correct I was able to repeat it two more shots. Looking back I should have factored coriolis in that shot given a 3 second flight time, but thats another ten miles of bad road we can discuss later.

What I envision in my head is the top everyone keeps referring to. Spin that top hard and its got a nice tight twist on its' center. As soon as it looses the centrifigal inertia it starts to wobble. We've all seen it our whole lives. I envision a bullet doing the same thing, drawing the circle instead of drilling a hole. But the bullet is not sitting on its nose spinning with gravity pulling it down to the table. A bullet is spinning and traveling horizontally as well as a verticle fall as opposed to the top that is stationary on the table and only spinning.

Cant say that what I'm writing is the gospel and should be put in the text book, but that is how I understand it.

What I think you're describing is the decay of rotational velocity (RPMs). I believe it DOES happen but it's not in proportion to forward velocity decay due to drag. I think it's a whole nuther ball of wax.

What I'm prodding you on is trans-sonic buffeting. Some say it is not a real phenomenon...I don't have an opinion and haven't delved into it. Maybe it's not that big a deal with high BC bullets...I know lots of rim fire enthusiasts think it is a big deal but they're shooting low BC stuff at very modest velocities.

Maybe I'll look into it in depth one day. For now easy answers are all I'm after!

The bullet design has a lot to do with how well a bullet perfoms through the transonic region. Look at the various 308 bullets some with lower or higher bc but there are certain ones that are known to transition poorly like tge 1y8 smk. It is said that the problem with it is the degree angle of the bt.

We're in agreement. Yet the loss of foward velocity is directly related to MV, BC, temp, and DA. I expect the transition of supersonic to subsonic as well as the loss of RPS to be (if not simultaneously) very near to each other in distance and within near equal time of flight.

Barrel twist and bullet length are only part of the equation. Im on the ranch now w no manuals etc so bear w me. A 6.5mm 140 gr fired at 2000 fps may not stabilize in an 8 twist barrel and the same bullet may stabilize in a 10 twist if fired at 3600fps. I doubt a bullet fired with high enough RPS to be Stabilized at 100 yds would loose enough to destabilize over a 3 second flight. There is very little in the air to slow the spin.

Just my thoughts
TC

I agree with that completely. I may not have been clear, but that is what I meant to say. The decay in spin is not near as great as the forward velocity losses. I believe you're correct about higher velocities also. Greenhill recognized that higher velocities allowed for a slower rate of twist for a given bullet length.

Clear as mud to me.

My observation as well.

Take a 140 gr 6.5 mm in a 1:9" twist. Fill that case full of fuel and it will shoot However you may be on the high end of pressure and you may be trashing brass.

Take a 1: 8.5" twist (appropriate) and load the 140 and it'll work slow or moderate speed.

140 gr in a 1:8" twist will have a lower MV where, in the powder charge node, it starts to shoot.

If day one, basic hand-loading and external ballistics was class 101. This might be 106 approaching Master's degree courses. Just a SWAG.

Then you get into internal ballistics and it is a whole other course.

Wish I had taken pics of the targets when working up loads for the 22-243, never got a keyhole but those Berger 90gr VLD were shooting more of a shotgun pattern until right at max loads where they settled into sub 3/4 inch, from an 1:8 barrel. As velocity increased the "groups" shrank from 7 inches + to the 3/4 inch, .3gr more got to a sticky bolt.

Good discussion, and from my limited knowledge spot on conclusions were reached

OK, we're talking semantics here, but think about it... there is no such thing as "overstabilized," because the word itself is an oxymoron. Something is either stabilized or it's not. If it's OVERstabilized, it ain't stable; therefore by definition it's unstable. Yes, you can definitely spin a bullet too fast, but that's only because doing so can expose the limitations of the bullet itself, not that there's a case of "too much of a good thing." Using the term "overstabilization" to describe what happens when you do so is like saying a woman is "excessively pregnant." It's just an inaccurate term that doesn't accurately describe what is actually happening.

If you spin a bullet too fast, the increased RPM amplifies any imbalance in the bullet, and lighter bullets are harder to build perfectly concentric and balanced than heavier bullets because any tiny imbalance represents a greater % of its total mass. That isn't "overstabilization," it's a case of spinning an imperfect projectile too fast and inducing wobble as a result of the imbalance.

The fact is, if you're shooting a perfectly balanced light, short bullet, entering the lands square, and the load is tuned to the rifle, too fast a twist will not negatively impact achievable precision, provided the bullet can withstand the forces of being spun so fast.

The "overstabilization" thing was a hot topic in precision shooting for years, but has been disproven over and over again as bullet manufacturing precision has improved and shooters have gone to faster twists to shoot high BC bullets, yet noticed their light bullet accuracy didn't suffer as a result... at short range, medium range, and long range.

Sorry brother, not trying to be argumentative, but it is indeed a myth.

To answer to Ron's original question, the 6.5's are popular in Sweden for Elk (European Moose), which by law requires the 156/160 grain class of bullet. Most American shooters are happy with 140's.

Everything I've read or seen is that the longer the bullet (heavier) the harder it is to get balanced perfect compared to the short lighter pills. This is all with a c&c type bullet. I haven't seen much study into the monolithic type hunting bullets though.

Too much gyroscopic stability is no myth. For most practical purposes as riflemen, it only is a bother when accuracy at TYPICAL range is affected...but when the muzzle is elevated six or eight degrees too much gyroscopic stability would definitely be detrimental to accuracy. It's not seen because those who shoot at these ranges are equipped properly in the first place. The center of pressure MUST be allowed to act in order to keep the axis of rotation tangent to the trajectory path. An example would be gyroscopically stabilized artillery shells. They have to impact nose-first in order to activate the fuse. If they belly flop onto the target the don't detonate reliably---never mind the problem of calculating trajectory in order to achieve a hit.

Overstabilization is a real phenomenon.

Here's an interesting Web page about external ballistics in artillery. The projectiles may be much larger than what we shoot out of our rifles, but the principles are the same.

http://nigelef.tripod.com/fc_ballistics.htm

See link below. Ballistician Brian Litz explains why "overstabilization" is a myth as it applies to sporting firearms bullets, and why you can't compare the behavior of rifle bullets in flight to artillery shells. His answer to the question posed is in the responses at the bottom of the page:

http://bulletin.accurateshooter.com/2013...spin-a-problem/

This doesn't mean you can't overspin a given bullet for the reasons already stated. It's just that if a bullet is well-balanced, spinning it an "too fast" an RPM doesn't impair precision as long as the bullet is structurally capable of withstanding the higher forces.

If the "overstabilization" theory was true, then plenty of ARs with 1:7 twist barrels shooting 50 gr. .224" bullets into sub-moa groups at distance wouldn't be possible. My own testing with fast twist barrels and light bullets in multiple bore diameters disputes the "over" claims.

You're not reading carefully enough. Litz dismisses it...for "practical purposes." And that IS correct. I've stated MORE than once that most of us don't shoot 2500 meters.

You're talking about shooting 50-grain bullets out of 1-7 ARs, and you're never going get the kind of range out of that number to see the effects of overstabilization.

Analyze the world record confirmed sniper kill...it was reported about a year ago IIRC. Take a look at the angle of departure and consider how that bullet would have performed had it been gyroscopically rigid. Litz says overstabilization is not a problem with flat fire trajectories. A 2700 meter shot does not travel a flat fire trajectory.

Overstabilization is real. It's just not something we have to deal with ordinarily.

A direct quote from Bryan Litz in response to a Q&A on this topic:

"Regarding over-stabilization; the 'common knowledge' that you hear often is that a bullet which is spun too fast will not trace with the trajectory, in other words, it will point 'nose high' on the downrange leg of the trajectory, thereby causing extra drag and lowering BC.
This explanation comes from high angle artillery shells which are far more massive, fly to very high altitudes (thin air) and arc thru dramatic angles over their trajectories. On this scale, it's true that spin stabilized projectiles can fail to 'trace' and fall belly or base first.
However, in the realm of small arms ballistics which usually occur below 10,000 feet ASL, projectiles weight less than 1 pound, and trajectories typically only arc a couple degrees (120 MOA) max, the flight dynamics are very different.
Spinning a bullet faster has the effect of increasing spin drift, but not increasing drag. In fact, over stabilizing (I prefer the term 'super stabilizing') can have the effect of suppressing the limit cycle yaw angle of the bullet, and cause it to fly with a higher BC over long range."

Since the topic pertains to small arms barrel twist rates, real world results pertaining to the subject of small arms bullets is what's germane here. Again, it's always better to err on the side of "too fast" than too slow a twist, and you're far more likely to have stability problems with the latter than the former with bullets of ANY weight/length.

Uhhh...excuse me, but NO, you don't get away with that. What's germane here is that you've asserted that overstabilization is a myth. Even Litz acknowledges its existence, if you're astute enough to pick up on what he says.

"However, in the realm of small arms ballistics which usually occur below 10,000 feet ASL, projectiles weight less than 1 pound, and trajectories typically only arc a couple degrees (120 MOA) max, the flight dynamics are very different."

Uh, yeah. As I've suggested, you should do a little analysis on the world record confirmed sniper kill. Fireman JG can provide a little data if you need it and ask for it---if you can figure out just what it is you need. I'll just clue you in right now: the trajectory on that shot exceeds 120 MOA by far. It's at least 12 degrees (that would be 720 MOA minimum and is probably a LOT more than that due to the parabolic shape of the trajectory).

And try to comprehend that the statement "spinning a bullet faster has the effect of increasing spin drift, but not increasing drag. In fact, over stabilizing (I prefer the term 'super stabilizing') can have the effect of suppressing the limit cycle yaw angle of the bullet, and cause it to fly with a higher BC over long range" pertains to low angle trajectories.

I'll never understand peoples' emotional attachment to irrational positions in arguments of this nature.

I totally understood what he said. Of course it pertains to low angle trajectories, i.e. any shot you're ever going to make with a centerfire rifle! You're moving the goal post with your 720MOA sniper shot example, because it has ZERO relevance to the topic of hunting rounds and typical hunting shots, even very long range ones. In addition, Litz was using 120MOA as an example to illustrate a point, not as an absolute ceiling.

I repeat, the overstabilization thing IS a myth, because every time the subject of overstabilization is brought up on internet forums, the context of the subject is pertaining to small arms bullets. The casual reader understands we're talking about shoulder fired centerfire rifle bullets here, per the title of the thread. Since small arms bullets don't behave like huge artillery projectiles traveling in extreme rainbow arcs, the comparison is irrelevant. This is an important distinction to make because believing in the "overstabilization" theory leads people to shy away from fast twists, when in fact going with a fast twist (in a quality barrel blank, using quality bullets and precision loading techniques) gives you far more versatility than trying to choose the old "rules of thumb" of 40 years ago and is a better choice today, using today's bullets. The original subject of this thread is 8 and 9 twist for 6.5mm. My position isn't an emotional one; I'm simply relaying what my own experience from popping a lot of primers has shown me. If that irritates you, I'm truly sorry. We'll just have to respectfully disagree.

So, because I disagree with you, I'm the one being "irrational?"

Scroll down to the middle of the page at this link:

http://anarchangel.blogspot.com/2007/01/stabilization-mythology.html

Also, gunwriter John Barsness did a pretty good article about this in Rifle magazine a couple years ago, where he debunked the overstabilization theory as well. I had the issue and looked for it, but couldn't find it, but you might be able to find excerpts from it online somewhere.

I moved no goalpost. The argument that overstabilization does not exist is bound entirely in semantics. I agree and have stated that it won't be an issue for most of us except for instances in which it exaggerates bullet imperfections affecting accuracy or causes structural failure. But it exists nonetheless.

Ok, since we're riding the semantics merry-go-round, how about this:

You're not going to run into any problems by having a faster barrel twist than typically recommended for a bullet weight range, as long as you're shooting quality bullets, have a quality barrel, and use precision loading techniques. If you do that, It doesn't matter the shot distance, this "overstabilization" issue is a non-existant concern.

That's ultimately what the shooter who is selecting a barrel twist is concerned with anyway, whatever assignable cause and terminology you wish to give to a barrel and load combination not yielding the desired results: "Does the twist rate selected shoot the bullets I plan to launch well?"

My point... shooters have discovered that the old "rules of thumb" about twist is flawed. "Accepted wisdom" aint always right. There is much greater risk of poor precision from too slow a twist than too fast, and a fast twist barrel will shoot a much wider range of quality bullets well than a slow twist barrel will, all else being equal. When a fast twist yields poor precision with a given bullet, the culprit for the poor precision is the bullet itself and/or the bullet's seating distance to the lands and/or the load not being tuned to the rifle, not the twist being "too fast..." as long as the bullet is structurally capable of withstanding the RPM in the first place. Otherwise, the "too fast" twist would shoot ALL bullets of a given weight/length poorly, and that just ain't so.

For any theory to be indisputably true, it has to be repeatable and reproduceable. The number of shooters who routinely shoot light bullets in fast twist barrels with sub-MOA precision disproves the "overstabilization" theory. To compare centerfire rifle bullets to artillery projectiles is like advising one on the best tires for a formula 1 car when they were asking about recommended offroad tires for a 1982 Ford Bronco. Sure, they're both automobiles with 4 tires, but that's where the similarity ends.

If we agree on that, great. If not, let me just preemptively say "you're right; I'm wrong" now and we move on. Either way, I think the point has been made and beat to death. Peace.