Bullet Stability In Flight— Modern Bullet Tips

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Roamin_Wade

Roamin_Wade

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When these ballistic tips came out, they were just little tips taking up maybe 10% of the projectile length. Now, these tips are up to a third of the projectile length. I would think so much mass at the aft of the projectile and hardly any in the front would cause inaccuracy. Can anyone dispel this?
 

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I can't give you any scientific reason why they should be any more or less accurate. But all of the most accurate target bullets use them, or something similar. I doubt if it is hurting accuracy even at close range. At longer ranges the difference is huge.

They serve 2 purposes. The primary purpose is to make the bullet more aerodynamic. Some use a plastic tip, some like the old Winchester Silvertips used aluminum, and Remington at one point used Bronze before going to plastic. And some like the Berger and Scenar bullets use a hollow cavity at the front of the bullet. This makes a lighter bullet as long or longer than a much heavier bullet. This gives the shooter the benefit of the speed possible with light bullets and the aerodynamics usually only possible with much heavier bullets

From a long range target shooting perspective having the bullets longer results in a much higher Ballistic Coefficient which means they retain speed much better down range. The difference can be significant. A 155gr Scenar bullet has a BC of .508. A 150 gr Nosler Partition only .387, and even a Hornady SST 150 is only .415.

From hunters perspectives the plastic tips drive into what is essentially a hollow point bullet aiding expansion. The ones with hollow a hollow cavity in the front tend to stay together for 3-4" after impact then basically explode inside the animal. Both types can be very effective hunting bullets.

01_95-75-and-Berger-692.jpg
 
Roamin_Wade said:
When these ballistic tips came out, they were just little tips taking up maybe 10% of the projectile length. Now, these tips are up to a third of the projectile length. I would think so much mass at the aft of the projectile and hardly any in the front would cause inaccuracy. Can anyone dispel this?
Click to expand...
The further aft the CG relative to the center of pressure, the more spin is required for static stability. However, don't confuse low static stability with inaccuracy.
 
lysanderxiii said:
The further aft the CG relative to the center of pressure, the more spin is required for static stability. However, don't confuse low static stability with inaccuracy.
Click to expand...


Static is when something isn’t moving. Both the spin of the bullet and its forward motion are dynamic, not static. I’m not certain what the term “center of pressure” means but the CG on a projectile with an extremely long plastic tip means that the CG is further back than it would be if the bullet had a small plastic tip and/or a bullet with soft lead point or FMJ. I guess a good way to look at my question is to imaging a feather being thrown with the feather end first. It wouldn’t be long before it would switch ends in flight. That’s a gross comparison as opposed to a bullet in flight but I think it illustrates my concern.
 
Here’s an anecdotal point to consider regarding ballistic tips.

For those that are serious about competing in F Class and Bench Rest matches (I’m talking about guys who not only sort their brass and bullets for consistency but also weigh/sort their primers), you will rarely, if ever, see them shooting ballistic tips
 
Long ogives move the center of pressure rearward. Boattails move the center of mass forward, the same as the poly tips move the center of mass rearward, so you’re still able to control the relative position of the center of pressure versus the center of mass.
 
Roamin_Wade said:
Static is when something isn’t moving. Both the spin of the bullet and its forward motion are dynamic, not static. I’m not certain what the term “center of pressure” means but the CG on a projectile with an extremely long plastic tip means that the CG is further back than it would be if the bullet had a small plastic tip and/or a bullet with soft lead point or FMJ. I guess a good way to look at my question is to imaging a feather being thrown with the feather end first. It wouldn’t be long before it would switch ends in flight. That’s a gross comparison as opposed to a bullet in flight but I think it illustrates my concern.
Click to expand...
That is not what static stability means. Airplanes in flight have static stability, Rockets in flight have static stability, and bullets in flight have static stability.

Static stability in the case of bullets, it is the tendency of a bullet to remain in the attitude they were in at launch, ie not tumble. The spin of a bullet is what allows a bullet to have static stability.

Dynamic stability is the nature of a bullet's static stability with regards to perturbations to initial attitude.

If a bullet is statically unstable, it will tumble. If a bullet is statically stable, but dynamically unstable, the bullet will remain in stable flight until something, wind, a speck of dust, muzzle blast, anything, induces a yaw, and at that point the yaw will increase until the bullet departs stable flight. If a bullet is statically stable and dynamically stable, any yaw will be damped to zero.

A bullet flying through the air is never perfectly aligned longitudinally with the wind, the wind is never straight along the long axis of the bullet. For one, the bullet is moving forward and dropping at the same time, so it always has some angle relative to the wind. Anything moving in an asymmetrical airflow (it has an angle of attack, or in this case - yaw) over its surface will produce lift. That lift can be represented as a vector acting on a point in the body, that point is the center of pressure. The distance from the CG to the CP times the lift force perpendicular to the longitudinal axis of the bullet is the "over turning moment". The over turning moment will tend to push the nose of the bullet into greater yaw angles.

If the bullet has sufficient spin, the gyroscopic moment will push the nose so as to reduce the yaw, it is statically stable.

Here is a primer on exterior ballistics.

By the way, a round ball has a CG and CG in the same place, the center of the ball, and is statically neutral, neither stable or unstable. If you design a projectile with the CP behind the CG, and arrow with the fletching at the rear, it will be stable without the need to spin it, but still might be dynamically unstable.
 
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lysanderxiii said:
That is not what static stability means. Airplanes in flight have static stability, Rockets in flight have static stability, and bullets in flight have static stability.

Static stability in the case of bullets, it is the tendency of a bullet to remain in the attitude they were in at launch, ie not tumble. The spin of a bullet is what allows a bullet to have static stability.

Dynamic stability is the nature of a bullet's static stability with regards to perturbations to initial attitude.

If a bullet is statically unstable, it will tumble. If a bullet is statically stable, but dynamically unstable, the bullet will remain in stable flight until something, wind, a speck of dust, muzzle blast, anything, induces a yaw, and at that point the yaw will increase until the bullet departs stable flight. If a bullet is statically stable and dynamically stable, any yaw will be damped to zero.

A bullet flying through the air is never perfectly aligned longitudinally with the wind, the wind is never straight along the long axis of the bullet. For one, the bullet is moving forward and dropping at the same time, so it always has some angle relative to the wind. Anything moving in an asymmetrical airflow (it has an angle of attack, or in this case - yaw) over its surface will produce lift. That lift can be represented as a vector acting on a point in the body, that point is the center of pressure. The distance from the CG to the CP times the lift force perpendicular to the longitudinal axis of the bullet is the "over turning moment". The over turning moment will tend to push the nose of the bullet into greater yaw angles.

If the bullet has sufficient spin, the gyroscopic moment will push the nose so as to reduce the yaw, it is statically stable.

Here is a primer on exterior ballistics.

By the way, a round ball has a CG and CG in the same place, the center of the ball, and is statically neutral, neither stable or unstable. If you design a projectile with the CP behind the CG, and arrow with the fletching at the rear, it will be stable without the need to spin it, but still might be dynamically unstable.
Click to expand...

I see in that article where the static stability is also referred to as gyroscopic stability. That makes more sense to me using that term. Basically you are saying that it is static along the longitudinal axis. While bullets need the gyroscopic stability to maintain that axis to remain static (unchanging), an aircraft is “trimmed” to maintain the stability along its longitudinal axis. Control surfaces then are able to move around and/or about that axis. I see what you mean.
I used to balance turbine and compressor rotors and static unbalance is where an element will roll downward and cause the unbalance to settle downward. Dynamic unbalance is the unbalance sensed as it is being turned. Therefore one is static (not rolling) and when it rolls, it is considered dynamic because both ends of the rotor can be balanced separately. I’ve also studied aircraft physics when I became an aircraft mechanic and learned the “along, about and around” axis’ of an aircraft in flight.
 
Roamin_Wade said:
When these ballistic tips came out, they were just little tips taking up maybe 10% of the projectile length. Now, these tips are up to a third of the projectile length. I would think so much mass at the aft of the projectile and hardly any in the front would cause inaccuracy. Can anyone dispel this?
Click to expand...

QPI3LgC.jpg
 
skeeterfogger said:
That's why I just use standard sp. Short, long, works. Add in boat tail and good to go.
Click to expand...

You have told us what you do, not why.

Why do you use only soft points?

(ostensiby, because of the thread title and subject, they are more accurate. What have you discovered of their accuracy? Or perhaps it was some terminal effect not inline with your course of quarry?)



Like everything in this planet, polymer tips are a compromise.

Just as @jmr40 said, the tips initiate better expansion at the cost of a smidgen of weight.
The poly tips increase the ballistic coefficients at the cost of a bit of stability.
The boat tails reduce drag at the cost of slightly less muzzle exit stability.

But, for all those deficits, they work better at longer ranges than blunt faced, square butted benchrest bullets.

For short range the added expense for the traits that are actually detrimental to the sport is unnecessary.
Benchresters put all that money into consistent projectiles.


Roamin_Wade said:
Can anyone dispel this?
Click to expand...

See the latest PRS circuit results.
Long distance.
Fancy bullets.
Extreme presicion.

If there was a myth of inaccuracies of tipped bullets, they would have found it.

I don't keep up with them. For all I know they could have started using all aluminum bullets...:)

I do know that I use them because I like the little red points, they look cool.;)
 
Nature Boy said:
Here’s an anecdotal point to consider regarding ballistic tips.

For those that are serious about competing in F Class and Bench Rest matches (I’m talking about guys who not only sort their brass and bullets for consistency but also weigh/sort their primers), you will rarely, if ever, see them shooting ballistic tips
Click to expand...
Less accurate does not equal inaccurate.

That's kind'a like saying guys that are serious about cars, (F1, etc), aren't driving stock corvettes....
 
lysanderxiii said:
Less accurate does not equal inaccurate.
Click to expand...

Didn't say ballistic tips were inaccurate, did I?

But taking you point, accuracy is relative to the individual shooter's objectives. For some putting 3 rounds in a pie plate at 50 paces is accurate enough. For others anything more that a 1.5 inch 5 shot group at 600 yards is inaccurate. Those the latter group don't shoot ballistic tipped bullets.
 
Roamin_Wade said:
When these ballistic tips came out, they were just little tips taking up maybe 10% of the projectile length. Now, these tips are up to a third of the projectile length. I would think so much mass at the aft of the projectile and hardly any in the front would cause inaccuracy. Can anyone dispel this?
Click to expand...

I have no technical data to present to you. My suspicions say, you are correct. Thus, I think, the move toward a harder/tighter rifling spin in many rifles. This becomes more apparent when you decrease velocity to shoot through a silencer, or decrease rates of rifling spin, maybe in an older rifle. I stay away from spitzers and boat tails in silencer work for that reason. I use a conventional copper/lead round nose bullet to keep the weight spread as evenly over the bullet's length as I can.
An easier way to observe destabilization, might be when it strikes gelatin, or soft game animal tissue. Shooting the bullets out past the point of being supersonic would likely show yaw as well, and a more dramatic increase in group size.
 
Demi-human said:
See the latest PRS circuit results.
Long distance.
Fancy bullets.
Extreme presicion.
Click to expand...

Nature Boy said:
For others anything more that a 1.5 inch 5 shot group at 600 yards is inaccurate. Those the latter group don't shoot ballistic tipped bullets
Click to expand...

And, because I was interested, I went to the Precision Rifle Blog and read up on exactly “What the Pros Use”.

Go figure. The best of the best shooters use, the best of the best components. Berger, Lapua, Sierra. Hornady was a distance fourth.:(

Obviously, and I knew better, Berger is the best. And they don’t make any tipped bullet. Used more, by a wide margin, nearly four to one.

Rather than myself try to use the best for my meager efforts, I shall stay with my lovely red tipped bullets and refrain from straining the market further.;)

I am not good enough to spend thrice the dough on bullets anyway.
 
Hornady (maybe others, dunno) has/have figured out that the plastic tips on most bullets heat to the melting point due to air friction. They have introduced a line of bullets that have tips that do not deform
 
Nature Boy said:
Didn't say ballistic tips were inaccurate, did I?

But taking you point, accuracy is relative to the individual shooter's objectives. For some putting 3 rounds in a pie plate at 50 paces is accurate enough. For others anything more that a 1.5 inch 5 shot group at 600 yards is inaccurate. Those the latter group don't shoot ballistic tipped bullets.
Click to expand...
You can get much better accuracy out of tipped bullet than "3 rounds in a pie plate at 50 paces"....

With the right loads and the right rifle, they'll out-shoot you.
 
redneck2 said:
Hornady (maybe others, dunno) has/have figured out that the plastic tips on most bullets heat to the melting point due to air friction. They have introduced a line of bullets that have tips that do not deform
Click to expand...

I haven’t hit anything more out to 1600 yards with ELD’s (heat resistant) than I ever did with A-max’s. The BC is easier to tune - more stable for various ranges, but as @Nature Boy pointed out, the “step change” to heat resistant polymer tips was about as tall of leap as a sheet of paper.
 
Roamin_Wade said:
When these ballistic tips came out, they were just little tips taking up maybe 10% of the projectile length. Now, these tips are up to a third of the projectile length. I would think so much mass at the aft of the projectile and hardly any in the front would cause inaccuracy. Can anyone dispel this?
Click to expand...
Have you actually shot any of these bullets?
 
One critical aspect @Roamin_Wade overlooked in the assumption of bullet balance is the consistency of the tip and the importance of consistent BC in long range shooting.

Many BTHP’s suffer from inconsistent tips, so guys will spend time trimming meplats and pointing bullets - adding a lot of effort to already expensive bullets. Or... a guy can get nearly the same short range group size with a more consistent BC out of the box, at a low cost.

The polymer tip is also an advantage for driving expansion at lower speeds. Like having a built in anvil to help open your bullet. So in long range hunting applications, expansion ferocity and reliability are improved by the poly tip. A high BC BTHP may not really be an HP, but rather an OTM, and might have issues opening reliably at low velocity/long range. Pull the meplat back to help improve expansion reliability, and you lose BC...

If you’re shooting for low Agg’s, poly-tipped bullets probably aren’t the right direction. If you’re hunting at long range, or banging into steel at variable distances at low cost, they have their place.
 
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