Why the 6.5's Need for 8 twist or 9 twist by bullet weight??

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.

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.

I think we're in general agreement, Ted. I do agree that for all practical purposes, overstabilization is not an issue---until it becomes an issue, and I think you know what I mean by that. I guess the whole argument actually revolves around what a practical range really is. For me, even 800 yards exceeds the limit of practicality.

Peace, right back at ya. I think you're okay.

Now I'm gonna make things worse...

We'll reference that longest confirmed kill of 2707 yards. The data I have of a 338 LM with a 300 gr VLD, in my current conditions gives a correction of 41.6 Mils (and way subsonic in Fannin county, TX)

41.6 x 3.43 = 142.69 MOA

But!!!!! The bullet does not rise that far above a level line from the shooter. That is only hold over.

Maximum Ordinate.

If I had my Kestrel I could tell what it is. I remember looking at it with a 308 and 178 A-maxes. The elevation was almost 10 Mils (so 30' above the target at the target) but the maximum ordinate was around 8'. The bullet departs from the line of sight which we can only see in straight lines.

I think I remember asking you about the trajectory of that shot and I think you supplied me a trajectory table to go along with it. I don't recall the numbers but it seems like the angular difference between the first 100 yards and the last 100 yards was about 12 degrees once I did all the trig.

12 degrees of rise on the departure side from the barrel?

No. An approximate 12 degree difference between the first 100 yards of bullet trajectory and the last 100 yards of bullet trajectory.

That seems small...

I may have made an error. Even of my calculations were sound, there is definitely a certain amount of error. I only wanted an approximation. The true result would be greater than my approximation.

Had I not lost my Kestrel on an elk hunt I could find the height above the ground and it would be easier to figure out the rest.

Can you generate a trajectory table in 25 yard increments? That would provide enough info to get it really close.

I can, but it will show scope elevation correction, not actual bullet path.

I havn't looked at JBM to see of they can tell max ordinant and I'm on my phone away from a computer until tomorrow.

Hornady Ballistic calculator shows the bullet path and comeup in inches.

What I'm looking for is the slope of the trajectory path out of the muzzle and the slope of the path the last few yards. A trajectory table in 25-yard increments should get close enough for rough calculations..

Go to jbmballistics.com

I'm betting a 300 gr. SMK. is what was used. That's a SWAG though.

Input a G7 of .381
MV of 2700 fps

I'll work it out again when I'm at home with my PC.

Recalculated. I did it my way using QuickTarget and I did it using the trajectory calculator at jbmballistics.com. I was surprised at how closely the two techniques agreed.

The actual figure is about 8.5 degrees. Approximately. A more precise method would probably add just a smidgeon to that but probably not enough to mean much at all.

So, the bullet's nose would turn down about 8.5 degrees by the time it reached the target at 2700 yards---assuming that the axis of the bullet's spin remains tangent to the trajectory the entire flight (meaning the nose is pointed perfectly forward the entire trip to the target).

IF---and I am NOT saying it does, did, or anything of the sort---I am just saying IF the bullet was spun fast enough that it was gyroscopically rigid (aka overtabilized) its nose would be pointing up at an angle of about 8.5 degrees at a range of 2700 yards...but that is really a gross over-simplification. It would have traveled some distance in a nose-up attitude and that would screw the entire calculation up way before 2700 yards because all the calculations are based on an ideally stabilized bullet. Nonetheless, the bullet would not be achieving full potential BC as the spin axis began to deviate from the flight path trajectory, and I think it would make a hit impossible.

I did that just for you, JG. You owe me three Wikipedia lookups!

10-4

Even if a bullet was overspun in the barrel it would need the extra spin to make if maintian correct flight that far out. I bet there is no way, no how the bullet would still be nose up aproaching a mile.

Hopefull within months a friend and I get to head to west Texas and sling some lead at a mile and beyond. We'll be taking steel and painting it white. If a bullet is impacting side ways it should show.

Videos and pics will come from the trip, I promise.

Thank you for all the research. 8.5 degrees still seems small, but I wont argue it. It drives home the facts I preach of bullets not reaching Red Tail Hawk soaring heights.

Did you come up with max ordinant on that shot?

Spin does not decay near as quickly as velocity does. You won't loose very many RPM as the bullet flies. It does decay a little, but it just isn't all that much. Plus, as the bullet slows, the influence of the center of pressure decreases---and that is the force that upsets the bullet's attitude in the first place.

I doubt you're ever going to see a target with bullets striking nose up consistently. I know you're anal about matching bullets and twist rates, strike one. Strike two would be that if someone managed to cause nose-up flight to happen via overstabilization, they'd never hit the danged paper in the first place. That kinda makes you think, doesn't it? I can't even think of strike three.

If you're asking about the highest point of the bullet's flight, one method gave me 1897 inches, which is 158 feet. That's a pretty high arc! But not that much relative to the 2700 yard shot...

So what's this about Red Tail hawk soaring heights? I don't read every post on the board...

I was meaning seeing bullets striking nose down. In other words, it's out of inertia and hitting the target like a rock thrown from the hand.

Red Tail Hawk soaring heights applies to this extreme range, but never 1000 yards and inside it. 1k seems like small potaoes compared to 2000 plus.

I have a THF member coming out for a class and will be bringing a rifle surely capable, and also a 300 black out. He asked, today, if we could push it really far. Sure I says as long as you have enough elevation travel in the scope.

158'?

The wind indicators you see does not represent the wind at the peak of bullet flight. An impressive shot, for sure!

Now that you mention it, thinking about the winds aloft makes a hit seem completely IMPROBABLE. I gotta wonder about it all...we hear about the hits, but I've never heard much about misses.

Misses are education. Range it, dial elevation, make a wind call, touch it off, if it misses see where it splashed. Cycle, correct windage (and elevation if needed) send round two, see what happens.

Ultra high BC, plenty of weight, and a decent muzzle velocity make shots that far about as challenging as my 7 Rem Mag at 1500- 1 mile. Tough, lots of factors, quick follow-up shot, but do-able if you're paying attention to everything. I don't hardly see how it's done without precision match ammo. Possibly lots of splashes happened prior to the record book hit.