Hey... long rangers... got a bullet / predictability question...

M

Magnum Wheel Man

New member
I just love to sit at my personal range & shoot paper as far as my range allows, which is 300 yards... I love playing with all calibers, from 17 to .375... & lately have been thinking about trying to stretch the distance more, & as I'm going through bullets developing loads, got me thinking...

one of my favorites is a custom fast twist ( 1 in 9" ) 22 K Hornet, I do OK with it to 300 yards, but started wondering about further ( I've not looked at the ballistic tables to tell me when it'll go subsonic... but...

I'm wondering if there is anything predictable when a bullet goes from super sonic, to sub sonic... & if there is a "type" of bullet that is more stable during the transition... if anyone would like to discuss, I'd appreciate any info I could glean... ( not necessarily just the K hornet ) could be something like my 7 X 57, or 6.8 SPC, or 223, etc...

I'm wondering if there is a predictability to the bullet after transition, & if a boat tail, is more stable or predictable than a flat base, & or a VLD, verses something "shorter" of a more traditional hunting profile... in general, if there has been an experimentation & documentation of bullet stability / predictability

thanks...
 
The one thing that comes to mind off the top of my head is boat tail angle.

The sharper the boat tail the less stable in the transonic region. This is why older lots of 180gr SMKs with the 9 degree boat tail shot better at long range than newer lots with the 13 degree boat tail (which was done for commonality of dies between the popular 168gr SMK).

Obviously if you are using a flat based bullet, this does not apply, and flat based bullets are often more accurate at close range than boat tails.

Jimro
 
thanks for the reply... my thinking, is perhaps the shorter ( easier to stabilize ) bullet might transition better... though since it's not as slippery, it likely reaches that transition point sooner???

so ( going out on a limb here ) perhaps a flat based bullet ( when used on a lower pressure, or shorter distance cartridge ) might actually be the better choice, if I'm going to shoot at distances where I'd cross that threshold ... for example ( again, remember I've not looked at the ballistics charts ) lets say I'm running a 55 grain bullet in my fast twist K Hornet ( I've stabilized up to 68 grain bullets with it so far )... with that 55 grain bullet I can hit 200 yards & still stay above the speed of sound, but by the time I hit 300 yards ( say 250 yards ) I hit "that wall" will the flight path be predictable enough to hit a target at 300 yards??? if I used a boat tail, would my 300 yards groups be better, or would the flat based be better, even if it hit the wall 25 or 50 yards sooner???

I guess I've never actually digested what a bullet goes through when it transitions, & if there is really any predictability after it does...
 
The reason the old Sierra 180 HPMK's stayed supersonic through 1000 yards was their higher BC than the new ones. The military 30 caliber M2 match bullet at 172 grains shot out as fast as the old 180 Sierra's also stayed supersonic. But the 168 HPMK went subsonic about 900 yards leaving a tiny bit faster.
 
Bart, don't some bullets tolerate the transition better than others?

I remember reading (like Jimro mentioned) the angle of the boat tail made some bullets do better than others when dropping subsonic.
 
... & can someone that shoots in that situation more often tell me what happens??? does the bullet completely destabilize & start tumbling, do they have a tendency to wing off in one direction or the other??? start dropping at an accelerated rate??? what would one expect to see on a target, 50 yards past the transition, 100 yards past, etc...

do you think it possible to shoot ( say that 22 Hornet, or 6.8 SPC ) through & beyond the transition, or does everything realistically end up off the target???
 
Yes, I think some bullets do transcend to subsonic with minimal (or none at all) trajectory change. RWS's R100 match 22 rimfire, 30 caliber 220-gr. and 45 caliber 500-gr. round nose ones. Both leave supersonic but the 22 goes sub before 100 yards and the 30-40 and 45 before 1000. All shot very accurate at respective max ranges in competition. I think it's due to their shape.
 
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Thanks BART... that's what I was hoping to discuss...

I've got more of a science brain, than long range experience... but my thinking was that the shorter the bullet, the less twist is required to stabilize it... so along that vein, they are easier to stabilize...

... it sounds as if bullets have a tendency to lose stabilization during the transition, so there is likely some point between round ball & VLD bullet shape, where the bullet continues with little deviation, on to it's target...

I was hoping there would be some with experience, ( or the knowledge to know where to look ) in order for me to come up with some sort of general basis in choosing bullets for my slower / less powerful cartridges, to play with going beyond their "normal" ranges...

a round nose flat based bullet is likely the shortest bullet practical ( although one could further this discussion with distance shooting handguns, & include semi wadcutter & wadcutter bullets ) I'm thinking there is some compromise in the middle, that will fly as far as possible above the speed of sound, yet will still be stable for a good distance after it goes through transition???
 
Bart B. said:
Yes, I think some bullets do transcend to subsonic with minimal (or none at all) trajectory change.
Click to expand...

IIRC, the designers of the .408 Cheyenne claim their cartridge is unique in that they specifically designed that bullet to remain stable when going transonic. It may be marketing hype, but reading up on what factors they found important might be interesting.
 
Thanks for the reference to the Chey Tach...

this from WIKI...

The Balanced Flight/Controlled Spin Projectile bullet patent has been questioned/disputed by the German physicist Lutz Möller.[10] Mr. Möller realized balanced flight has to do with the nature of spin stabilized flight and scale of parameters. There were projectiles produced prior to the patent that remain stable through the transonic flight regime. This is a consequence of the spin deceleration and forward deceleration of the projectile being similar enough not to cause undesirable precession and yaw during the transonic flight phase. The main parameter for achieving stable transonic transition is controlling the drag coefficients (Cd) and forward velocity loss around Mach 1 and to a lesser degree controlling the spin deceleration. In other words, any bullet with appropriate drag behaviour around Mach 1 and mass (distribution) will do exactly what the balanced flight projectile patent states.
Click to expand...

so... if I'm reading between the lines right, here, if the bullet shape & mass distribution are correct, the bullet will stay stabilized through transition...

in trying to over simplify again :rolleyes: a shorter round nose bullet may have the right properties ??? ( or perhaps a shorter pointed flat based bullet ??? say... aren't most 7.62 X 39 bullets of that shape ??? it may actually be a good cartridge to play with, as it likely goes subsonic before 400 yards ??? ) or is this also telling me, that I'd want as slow a twist as would stabilize the bullet, so it's rotational force is not too high when it goes through the transition??? or does it need more twist??? or just the "right amount" so it doesn't yaw in excess...

to throw that back to the handgun I mentioned earlier... I think wadcutters have a tendency to tumble at extreme distances... if this relates to the same reasons, then just the length of the bullet may not be the whole answer... it may be a balance of coefficient & bullet length ???
 
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Most bullet makers list the BC of their products. Put the numbers into a ballistic program, with your velocity, environmental conditions and you'll get an idea when the bullets go sub sonic.

I have "Shooter" on my I-phone. It highlights in red he distance where the bullet is sub-sonic.

Having said that, there are exceptions to the rule. There are some bullets that don't like velocity.

An example is BPCR. Using lead bullets if I push the velocity I loose accuracy.

I was shooting a BPCR Creedmor match and thinking the faster I shot the bullets the better.

WRONG. I found my 45-70 shot the 500 gn cast bullet better when I keep the velocity around 1100 fps at distance (we were shooting 800-900-1000 yards).

When I tried to push the limit on velocity, past 1500 fps, the bullets tumbles.

I backed off on the power and started hitting the gongs.
 
Magnum Wheel Man said:
There were projectiles...that remain stable through the transonic flight regime. This is a consequence of the spin deceleration and forward deceleration of the projectile being similar enough not to cause undesirable precession and yaw during the transonic flight phase.
Click to expand...


so... if I'm reading between the lines right, here, if the bullet shape & mass distribution are correct, the bullet will stay stabilized through transition...
Click to expand...

Yeah. If I'm reading between the lines correctly, it seems the bullet needs a big BC (to reduce forward deceleration) and a big radius (to reduce spin deceleration via bigger angular moment of interia). IOW, a big, long and heavy bullet, like the 419gr .408.
 
how about the 32-40 that used to be used for long range schutzen matches???

I kinda duplicated one using a heavy 8 mm barrel on my rolling block, when I built it...
 
Schuetzen matches were most commonly shot at 200 yards, not long range.

You might look up what the British do. They will shoot .308s at such long ranges as to ensure a subsonic arrival.
 
I work with a lot of aerodynamics engineers, some of whom are shooters. Here is the consensus:

A sphere will not suffer any destabilization in the transonic region. And this applies whether the sphere is spinning (rifled barrel) or not (shot cup).

Most handgun bullets are close to a spherical shape, and they will have minimal destabilazation. The bullets are short, fat, and blunt.

round nose and flat point rifle bullets will have some destabilization.

spitzer bullets will be the most destabilized, and the longer and pointier they are, the worse it gets. Of course, the longer and pointier they are, the more likely they stay supersonic for a longer distiance. Physics is a b!tch...
 
This shallow post of mine here will show you how little I really know about high speed aerodynamics.

But you have two types of drag, what we consider "normal drag" involving the interaction of the body and the fluid it is traveling through, and "wave drag" which "Wave drag is independent of viscous effects, and tends to present itself as a sudden and dramatic increase in drag as the vehicle increases speed. It is the rise of wave drag that leads to the concept of a sound barrier."

I would posit that the transonic stability has as much to do with shock waves inducing instabilities in the projectile. With a steep boat tail like the 168 SMK, the trouble would be, I guess, when the shock waves destabilize the viscous net drag, basically "blowing the base out of alignment."

Since bullets do not fly true to centerline of the bullet (the nose is always slightly off true, the base being dragged towards true by the net drag effect), the steeper boat tail angle must allow the shock waves to interact with the net drag effect in an asymmetric pattern, causing instability.

The only fella I know who had success at long range with the 168 SMK (1k and beyond) was using a very slow twist barrel, which is counter intuitive. But the less stable bullet would also require less energy to course correct meaning the nose could fly closwer to true as the net drag effect would have less stability to overcome, meaning the shock waves would be closer to symmetric. Of course smarter people than I have tried to figure for years why the 168 SMK doesn't do well in the transonic region. Don't take any of this as fact, it is purely my own thoughts on the matter.

Anyways, I think the sweet spot for long range bullets is a 7 to 9 degree boat tail. Any shallower doesn't seem to help the BC, and any steeper seems to induce instabilities in the transonic region (in almost every barrel save for one guy who claimed good results, at an unknown altitude, with a 1:13 twist barrel).

Food for thought anyways.
Jimro
 
I shoot the Lehigh 510-170 design which weighs 808 grains, coat it with Tungsten Disulfide, and propel it with 252 grains of powder to 2860 fps.
Works for me, in my circumstances.
YMMV.
 
An interesting bullet comparison between what was used 100 years ago for 800 to 1000 yard matches to what's used today can be seen in Sierra Bullets' web site. Here's the G1 BC numbers for two 30 caliber bullets weighing 220 grains:

220 grain round nose; about indentical to what was used in the .30-40 Krag Palma rifles shot out at about 2100 fps. Best accuracy with this stuff over a century ago was about 2+ MOA at 1000 yards; the best bullets made then would do.

Note: All the best 30 caliber bullets made until the late 1950's were FMJBT ones starting in the 1920's with the 30 caliber 172-gr. machine gun bullet made with best tolerances. In ideal test conditions, they would sometimes shoot about 1.5 MOA at 1000 yards but typically 2 MOA. Only after Sierra started making hollow point ones did long range accuracy get much better; testing sub MOA at 1000 was frequent. That was part of the reason back in the early 1970's the long range targets' scoring rings were reduced in size after being the same for about 80 years.

.310 @ 2600 fps and above
.371 between 2250 and 2600 fps
.378 between 1600 and 2200 fps
.410 @ 1600 fps and below

220 grain HPMK, about the heaviest bullet used for long range matches shot out at about 2850 fps:

.629 @ 2100 fps and above
.624 between 1700 and 2100 fps
.608 @ 1700 fps and below

Notice how the round nose one's BC gets bigger as it slows down whereas the HPMK's BC gets smaller.

I've shot both of Sierra's 13 degree boattailed 30 caliber match bullets (168 and 180) fast enough to stay supersonic through 1000 yards. Both easily shot under 1 MOA. Both from .308 Win. cases; 30" 1:12 twist (and a 26" 1:11 twist) for the 168's and 26" 1:11 twist for the 180's.
 
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hmmm... that's interesting... any speculation why the "slipperier" bullet gets less aerodynamic as it goes slower, & the "chunkier" bullet gets more aerodynamic???

I would have thought that, pretty much a constant, & both would have exhibited the same properties, just varying from their respective starting points???
 
Bart,

Those numbers make intuitive sense to me when you look at surface area to mass ratios.

The cylinder toped by a hemisphere will have less surface area than the cylinder with a boat tail truncated cone on the back and a tangent ogive on the front.

More surface area means more viscosity friction (normal drag), but the tangent ogive means less wave drag (closer to a Sears-Haack body type shape).

As speed decreases, wave drag goes towards zero, and the importance of surface drag increases in importance in calculating the overall net drag, so the projectile with the lowest surface to mass ratio will see the best performance at low speeds.

But when I say it is an intuitive answer, it means don't ask me to show you the math to back it up, as I don't have the surface area of either bullet in front of me.

Jimro
 
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