bullet expansion test results

[elkaholic]

It's fun to try After doing a lot of testing I mellowed out a lot about terminal performance because it's honestly amazing what all goes into terminal performance and it's really awesome just how good of function we do see over all out of all classes of bullets. Throat wear and fouling can make a difference in cup an core bullets, I've seen bullets exploding mid flight to excellent penetration just because of fouling from shooting two jacket types that did not like each other.
I find it fascinating, if it was not for the fact that I need less things to consume my time and money I'd be all over making my own bullets, it's absolutely fascinating!!!

Wanna buy my equipment!

 

[Rich Coyle]

It's fun to try After doing a lot of testing I mellowed out a lot about terminal performance because it's honestly amazing what all goes into terminal performance and it's really awesome just how good of function we do see over all out of all classes of bullets. Throat wear and fouling can make a difference in cup an core bullets, I've seen bullets exploding mid flight to excellent penetration just because of fouling from shooting two jacket types that did not like each other.
I find it fascinating, if it was not for the fact that I need less things to consume my time and money I'd be all over making my own bullets, it's absolutely fascinating!!!

At one time I had a Weatherby Mark V 7 Weatherby Magnum. I had it dialed with Nosler Ballistic Tips. It would put five inside 1" at 100 yards. Then I bought a Corbin press and made some bullets. WOW! I could put five of the home made bullets in 1/2" at 100 yards.

 

[toliver]

I have recently been talking with Hornady, attempting to solve a work related issue regarding terminal performance. As you would have it the latest tests show twist rate having a significant effect on terminal performance. As someone said centrifugal force. Basically lower rpm bullets penetrated deeper, faster not as much. They sent me some study results, here is part of a conversation as it pertains to me anyway. This is something they did recently. I found it interesting as it seems some have better luck than others with some bullets. lightbulb

.308 1/8 to 1/9 hugely increases rotation on the bullet and does a couple of things. One, it better stabilizes the bullet for extreme long range (not much interest to us necessarily) two, it creates a larger wound channel as the extra rotation causes it to expand better and three the extra rotation and as a result extra expansion causes 3" less penetration in a 1/10 over a 1/11.25 this is a good thing as we are trying to limit over penetration.

 

[elkaholic]

I have recently been talking with Hornady, attempting to solve a work related issue regarding terminal performance. As you would have it the latest tests show twist rate having a significant effect on terminal performance. As someone said centrifugal force. Basically lower rpm bullets penetrated deeper, faster not as much. They sent me some study results, here is part of a conversation as it pertains to me anyway. This is something they did recently. I found it interesting as it seems some have better luck than others with some bullets. lightbulb

.308 1/8 to 1/9 hugely increases rotation on the bullet and does a couple of things. One, it better stabilizes the bullet for extreme long range (not much interest to us necessarily) two, it creates a larger wound channel as the extra rotation causes it to expand better and three the extra rotation and as a result extra expansion causes 3" less penetration in a 1/10 over a 1/11.25 this is a good thing as we are trying to limit over penetration.

BINGO!! I have had people argue this over the years, but now "Uncle Hornady" says so!.......Rich

 

[Broz]

Well I have my first 9 twist 30 in my hands now. Back by popular demand will be the 215 Hybrids. So I will be watching for the loss of penetration. But if its just a few inches it may be had to tell the difference.

Jeff

 

[tbrice23]

Jeff, I took it for granted you had been using a 9 twist all along. I know you hunt at a much higher elevation but you've obviously been stabilizing those long pills in a 10 twist.?
All my 300wm and 300wsm barrels have 10 twists thus I dismissed buying such a long bullet being I hunt at 400 to 700 ASL.

 

[Broz]

Jeff, I took it for granted you had been using a 9 twist all along. I know you hunt at a much higher elevation but you've obviously been stabilizing those long pills in a 10 twist.?
All my 300wm and 300wsm barrels have 10 twists thus I dismissed buying such a long bullet being I hunt at 400 to 700 ASL.

When Berger released the 215 , the boxes stated 10 twist or faster. Then with the discovery 9 would stabilize them "better" way out there then started to recommend 9's. I still have many boxes that say 10 or faster. I have loaded them in many 10 twist 30's. Even 308's and never had a problem and I don't remember even reading of anyone have them not be stable in a 10. So, my newest rifle is a 9. I hope I didnt screw the pooch.


Jeff

 

[Trnelson]

Thought I'd shine a little more light on rotational force and dig out the old physics textbooks collecting dust in my library since college and run some basic calculations to illustrate the rotational forces acting on a bullet in flight. I used the 230g Berger 30 caliber as the model. A muzzle velocity of 3,000 fps and a 1 in 10" twist. This is just a snap shot of the force at a single moment, obviously this force degrades as both velocity and rpm decay enroute to the target...
The bullet experiences a force of 29,827.4 N or 21,999.5 Foot pounds, undoubtedly a significant factor in terminal bullet performance...

 

[smithjasona1978]

Ok. Please someone explain to me how with 22,000 pounds of force being imparted to that bullet in such a short period of time, how does the bullet retain its shape?? With that much force behind the bullet, forcing it to rotate down the barrel,why doesn't the boat tail become a flat tail? I always have wondered that. At the time of ignition It's under 60,000 psi inside of the case right?? I always wondered why the tapered boat tail of the bullets we shoot don't end up looking more like the flattened primer of a hot load.

And I am not doubting anyone's math or the physics of it.
But as Homer Simpson says...(I..don't get it.)

 

[Trnelson]

Ok. Please someone explain to me how with 22,000 pounds of force being imparted to that bullet in such a short period of time, how does the bullet retain its shape?? With that much force behind the bullet, forcing it to rotate down the barrel,why doesn't the boat tail become a flat tail? I always have wondered that. At the time of ignition It's under 60,000 psi inside of the case right?? I always wondered why the tapered boat tail of the bullets we shoot don't end up looking more like the flattened primer of a hot load.

And I am not doubting anyone's math or the physics of it.
But as Homer Simpson says...(I..don't get it.)

The abridged version is the time spent under that load is very small. Less than 0.002 of a second. Inside the barrel the bullet is supported along the bearing surface and copper jackets are noticeably thicker at the base of the bullet so that also helps to resist deformation. Cut one in half and see for yourself. Even so, I'm sure there has to be a slight change in the shape. I don't believe it's significant and I don't know if it could be easily quantified. Old school cast lead Minnie balls took advantage of the expanding gases to obturate and seal the bullet to the bore.

 

[smithjasona1978]

Not enough time. Got it. Thanks.

 

[Rich Coyle]

Also the pressure is evenly on the sides of the boat tail as well as the base of the bullet.

 

[RockyMtnMT]

My experience with testing low vel and stability factors lead me to the conclusion that a bullet with less than 1.5sg will cause the bullet to tip or yaw on impact. Like a top spinning, the faster the spin the harder to make it tip or knock off axis. When the bullet impacts and is not fully stabile it tips slightly and causes the hp to not take in hydraulics so it can expand. The smaller the hole the more apt it is to have a problem. As the stability is increased the longer the bullet stays oriented point forward as the bullet penetrates the medium. The better the bullets stays on axis the better it deforms and the better the wound channel is. Also the better the stability, or higher the stability, the longer the bullet will stay on its original path after impact and not change direction as it starts to yaw and eventually even tumble.

The more extreme the nose/ogive of the bullet gets the more the center of gravity of the bullet moves toward the base causing this to become more exaggerated on impact. In other words the heavier base of the bullet naturally wants to pass the lighter front of the bullet. Only the spin won't let it. On impact the spin degrades at a much higher rate than before impact and the natural tendency of the base to pass the nose comes into play causing failure or tumbling.

There is no formula or calculator out there that I know of that takes into account the shape of the bullet and what effect it has on stability. What I do know is it is easier to get consistent terminal performance from less aggressively designed (less pointy) bullets.

Bullets that have lead all the way to the point and not closed on the point do not need hydraulics to open up on impact. The lead is the hydraulic medium and causes the jacket to open up.

Tipped bullets have the potential of plugging the hole. In my opinion.

So stability plays a huge role in how terminal performance occurs. Stability is one of those things that most of us really knew very little about 10 years ago. As we become more advanced in our ability to shoot farther distances it is another thing that we should pay close attention to as hunters.

Steve

 

[Predator 22]

Tipped bullets have the potential of plugging the hole. In my opinion.


Steve

The plastic tip is designed to initiate expansion. Like a plunger upon impact. No hydraulic force necessary initially. Plastic tipped bullet cut aways show a wedge shape where the plastic meets the lead and where it meets meplat. Everything else you said was spot on, at least in my head.