*New Results* Forward Velocity vs Bullet RPM....which “hits” harder?

[AllThingsAI]

Anyone else read the chapter in PO Ackley’s book about shooting feral burros?

I haven’t read this...what does he say? I really need to read that book, I’m a big fan of his work.

 

[Tommie]

I haven’t read this...what does he say? I really need to read that book, I’m a big fan of his work.

Dude I could tell you, but anybody with the handle AllThingsAI just needs to own the books.

 

[AllThingsAI]

Dude I could tell you, but anybody with the handle AllThingsAI just needs to own the books.

Indeed!!!

 

[spaniel]

My 8-twist 22s and 243AI absolutely explode prairie dogs with VMAX and AMAX bullets. Red mist show. One trip I also took a 300WM with a 12 twist, shooting 125gr BT and 110gr VMAX bullets. I will say we noticed a significant difference in explosive factor with the faster twists. I was very disappointed with the explosive factor of the 300WM with 125gr BTs. I figured it should be roughly equivalent to the VMAXes in the other guns, which were lower velocity. Now the 110VMAX started to get to a similar performance range, but they were traveling 600-900fps faster than the smaller caliber/faster twist guns.

The caveat here is that this is a good thing for varmint type applications, but IMHO is irrelevant for larger game. You don't want exploding bullets imparting energy in a hog/deer because you will get much reduced penetration. Been there, done that with a smokeless muzzleloader bullet, it worked that one time but I wouldn't repeat the attempt.

 

[AllThingsAI]

My 8-twist 22s and 243AI absolutely explode prairie dogs with VMAX and AMAX bullets. Red mist show. One trip I also took a 300WM with a 12 twist, shooting 125gr BT and 110gr VMAX bullets. I will say we noticed a significant difference in explosive factor with the faster twists. I was very disappointed with the explosive factor of the 300WM with 125gr BTs. I figured it should be roughly equivalent to the VMAXes in the other guns, which were lower velocity. Now the 110VMAX started to get to a similar performance range, but they were traveling 600-900fps faster than the smaller caliber/faster twist guns.

The caveat here is that this is a good thing for varmint type applications, but IMHO is irrelevant for larger game. You don't want exploding bullets imparting energy in a hog/deer because you will get much reduced penetration. Been there, done that with a smokeless muzzleloader bullet, it worked that one time but I wouldn't repeat the attempt.

Solid practical information! Thanks for sharing. You are 100% correct about larger game, you need the right bullet for the job at hand. This is critter only territory, as much energy dump as possible in a short distance. Thanks for bringing that up, it’s important.

what were the velocities for your rifles? I would like to crunch a few numbers

 

[GotRDid]

You could call it the 'splody' factor like they reference in another thread.....

http://forum.accurateshooter.com/threads/splody-factor-v-max-verses-blitzking.4001262/

GotRDid.

 

[Webster]

Exactly, that’s my experience as well and the math supports it. But I want to quantify it so it can be optimized. My gut tells me that bullet length and cross-sectional area also come into play.

Don’t have a clue how you would quantify it. Many on this website have posted what bullets cause the most damage to small varmints. You need to do more hunting less tinkering.

 

[David Milisock]

My 8-twist 22s and 243AI absolutely explode prairie dogs with VMAX and AMAX bullets. Red mist show. One trip I also took a 300WM with a 12 twist, shooting 125gr BT and 110gr VMAX bullets. I will say we noticed a significant difference in explosive factor with the faster twists. I was very disappointed with the explosive factor of the 300WM with 125gr BTs. I figured it should be roughly equivalent to the VMAXes in the other guns, which were lower velocity. Now the 110VMAX started to get to a similar performance range, but they were traveling 600-900fps faster than the smaller caliber/faster twist guns.

The caveat here is that this is a good thing for varmint type applications, but IMHO is irrelevant for larger game. You don't want exploding bullets imparting energy in a hog/deer because you will get much reduced penetration. Been there, done that with a smokeless muzzleloader bullet, it worked that one time but I wouldn't repeat the attempt.

In my opinion comparing the expansion characteristics of VMAX projectiles in 22 and 24 caliber to 30 caliber is a reasonable demonstration of the effects of frangible projectiles VS less frangible projectiles. The 30 caliber 125 grain VMAX must have significantly more solid internal material compared to the 22 and 24 caliber or even the 110 grain.

The twist assuming a stable projectile is irrelevant, it's the velocity and lack of sufficient frangible projectile material that makes the 125's non viable. The slower 22's & 24's simply had the proper balance of frangible materials.

I would have thought that your 243AI would have had velocities well into the 3,600 FPS range. My 223 with 40 grain VMAX with 1 in 12 twists at 3,900 FPS explodes chuck heads within 350 yards, less explosive with body hits. I have 1 Remington 6MM with a 1 in 10 twist that shoots 75 grain VMAX at 3,900 FPS it also explodes chuck heads out tom500 yards less explosive with body hits. So assuming a stable bullet the twist is irrelevant to performance.

In fact the old Hornady 3rd edition used to list an extremely frangible 22 for the Jet that was designed to give explosive expansion at lower velocities, if memory serves warnings were given to use lower velocities and slow twist rifles.

 

[David Milisock]

The rotational force is most certainly there, simple physics. It indeed takes energy to induce spin, so there is an energy component with rotation. Like you mentioned the rotational component is what causes a bullet to explode...even with a raindrop if if too much force is applied. I want to know what the thresholds are. Once a bullet hits fur if it explodes radially (CF force) more energy will be dumped in a shorter span vs. a projectile that stays together or breaks apart with no radial (or minimal) component.

But that is what testing is for. As for gel, I’m not sure if it will actually show the affect I’m trying to test. I’ve never used it, but have seen lots of videos and articles. Pros and cons on each side. I think most people use it because it’s easy.

As for the Fur saving bullet vs hunting bullet comment you are correct, but that’s not an apples to apples comparison. The bullets have different mechanical properties. You can also spin that hunting bullet ALOT faster than a varmint bullet without it coming apart, so you could test a lower RPM hunting bullet with a much higher RPM hunting bullet...you just have to compare the same type of bullets.

The rotational force did not cause my 6mm to explode in the rain it was the velocity of the projectile hitting the wall of water at nearly 4 times the speed of sound.

Gel it the perfect medium for testing. Even handgun bulletts with medium tough projectiles penetrate about a inch before expanding and developing a secondary wound channel. A proper varment bullett will exhibit the same behavior.

A 1 in 8 twist at 2,000 FPS gets you 3,000 RPS, a 1 in 12 twist at 3,000 FPS gets you the same RPS. I can tell you right now the the same 22 caliber 40 grain VMAX projectile at 2,000 FPS 1 in 8 twist will not perform nearly as well as the 1 in 12 twist at 3,000 FPS. Both will be stable but one is a very close range varmint round but never really explosive the other explosive to about 200 yards.

 

[AllThingsAI]

You could call it the 'splody' factor like the they reference in another thread.....

http://forum.accurateshooter.com/threads/splody-factor-v-max-verses-blitzking.4001262/

GotRDid.

“Splody” is good!

The rotational force did not cause my 6mm to explode in the rain it was the velocity of the projectile hitting the wall of water at nearly 4 times the speed of sound.

Gel it the perfect medium for testing. Even handgun bulletts with medium tough projectiles penetrate about a inch before expanding and developing a secondary wound channel. A proper varment bullett will exhibit the same behavior.

A 1 in 8 twist at 2,000 FPS gets you 3,000 RPS, a 1 in 12 twist at 3,000 FPS gets you the same RPS. I can tell you right now the the same 22 caliber 40 grain VMAX projectile at 2,000 FPS 1 in 8 twist will not perform nearly as well as the 1 in 12 twist at 3,000 FPS. Both will be stable but one is a very close range varmint round but never really explosive the other explosive to about 200 yards.

Im sure you are right, but my hypothesis is there is a threshold And it will certainly be bullet dependent, mechanical construction of a given bullet is critical. 2000fps may not be the same as 3000fps...but is 3000 the same as 3500? It takes a lot of extra energy (powder) to get to 3500 or 4000.

I appreciate the input. Any specific type of gel?

 

[AllThingsAI]

Don’t have a clue how you would quantify it. Many on this website have posted what bullets cause the most damage to small varmints. You need to do more hunting less tinkering.

You do you and I’ll do me...I’m not looking for which bullet causes the most damage, that isn’t the point at all of this thread or test.

 

[David Milisock]

“Splody” is good!

Im sure you are right, but my hypothesis is there is a threshold. 2000fps may not be the same as 3000fps...but is 3000 the same as 3500? It takes a lot of extra energy (powder) to get to 3500 or 4000.

I appreciate the input. Any specific type of gel?

I like the academic aspect of the discussion, we have not interjected this but we can kill a varmint with anything, a head shot from a 22 or 45 caliber solid kills them. A body shot from the same kills them they just crawl away. However in my life I've know 3 incidents where varmint hunters using inappropriate projectiles had one go awry and hit someone over a mile away. Never anyone killed but a hit. An explosive varmint bullet reduces that risk quite a bit, good hunting practices and good varmint bullets nearly eliminates it. So you efforts may produce something useful good luck to you.

Not to be a pain in your butt but I've been shooting same fields for 63 years. In the last 15 years these fields have all gone to being terraced, now shooting across 500 or 700 yards of a field has the bullet traversing the normal wind changes but eddy currents at every terrace. Cutting across soybean to wheat to alfalfa introduces more currents. So reduced time of flight is the varmint hunters gift from rifle and cartridge manufacturers, I'll never slow the projectile down.

From my experience I consider 3,500 to 3,600 FPS to be the start of the hyper velocity range. Once you get there and start making regular hits there's no going back.

 

[AllThingsAI]

I like the academic aspect of the discussion, we have not interjected this but we can kill a varmint with anything, a head shot from a 22 or 45 caliber solid kills them. A body shot from the same kills them they just crawl away. However in my life I've know 3 incidents where varmint hunters using inappropriate projectiles had one go awry and hit someone over a mile away. Never anyone killed but a hit. An explosive varmint bullet reduces that risk quite a bit, good hunting practices and good varmint bullets nearly eliminates it. So you efforts may produce something useful good luck to you.

Not to be a pain in your butt but I've been shooting same fields for 63 years. In the last 15 years these fields have all gone to being terraced, now shooting across 500 or 700 yards of a field has the bullet traversing the normal wind changes but eddy currents at every terrace. Cutting across soybean to wheat to alfalfa introduces more currents. So reduced time of flight is the varmint hunters gift from rifle and cartridge manufacturers, I'll never slow the projectile down.

From my experience I consider 3,500 to 3,600 FPS to be the start of the hyper velocity range. Once you get there and start making regular hits there's no going back.

Nor should you slow them down, that’s what you enjoy!...Shoot em flat and straight. I’ll try to help you get to 5000fps, that would be fun!! That’s what’s great about shooting, we can all do it the way we enjoy! I enjoy understanding why things are happening, and I love highly optimized rifle cartridges. I might be shooting rainbows , but that’s fun too!

I would never tell anyone what they need to go do, that’s just wrong and extremely close minded. I enjoy learning and listening to people’s stories and wisdom and I appreciate people’s opinions. I’ve been wrong many times!

This is all for fun!

 

[David Milisock]

Nor should you slow them down, that’s what you enjoy!...Shoot em flat and straight. I’ll try to help you get to 5000fps, that would be fun!! That’s what’s great about shooting, we can all do it the way we enjoy! I enjoy understanding why things are happening, and I love highly optimized rifle cartridges. I might be shooting rainbows , but that’s fun too!

I would never tell anyone what they need to go do, that’s just wrong and extremely close minded. I enjoy learning and listening to people’s stories and wisdom and I appreciate people’s opinions. I’ve been wrong many times!

This is all for fun!

Please keep us posted on your results .

 

[Gb300wm]

According to science/math, bullet energy is much more affected by velocity than weight. If I remember right, energy is velocity squared x bullet weight divided by 450240 which is a constant. You can see here that velocity trumps weight because of the sheer physics here. Bullet rotation/rpm keeps the projectile stable in flight. I would not think any faster rotation than what’s required to keep the projectile stable would have any effect on it’s energy...

 

[RGRobinett]

Reduce this topic to how many rotations a bullet makes passing through, say, a 3" wide prairie dog, and it'll alter your belief - I can blame my altered state on one George Ulrich . . .RG

 

[AllThingsAI]

Reduce this topic to how many rotations a bullet makes passing through, say, a 3" wide prairie dog, and it'll alter your belief - I can blame my altered state on one George Ulrich . . .RG

Yeah RG it won’t make many rotations, that’s for sure, but that shouldn’t matter. The forces are already acting on the bullet in continuous time (it’s not a distance dependent function, no distance in the equation). Physics tells us if a bullet is spinning 2x as fast it has 4x the forces acting to tear it apart (the force acts in all directions)...just physics (Blame Newton, I’m just the messenger!) Hypothesis is Once the mechanical structure is compromised (from impact due to forward velocity the rotational forces will release nearly instantaneously. (Check out the CD video). BUT, that’s why I want to test so I can better understand the real dynamics involved, they are indeed very complex.

I’m guessing that cross sectional area and bullet shape also makes a difference...my gut says that short bullets will concentrate the force on a smaller area surface area...which will make them fail quicker (given the same type of construction as longer bullets). But I could be in left field here.

Maybe I can test using a .25 cal! . . I just don’t have the barrels.

Ryan

 

[AllThingsAI]

According to science/math, bullet energy is much more affected by velocity than weight. If I remember right, energy is velocity squared x bullet weight divided by 450240 which is a constant. You can see here that velocity trumps weight because of the sheer physics here. Bullet rotation/rpm keeps the projectile stable in flight. I would not think any faster rotation than what’s required to keep the projectile stable would have any effect on it’s energy...

Yep 1/2*mass*velocity squared....but there are multiple forces acting on a bullet. The forward vector force which what you describe, but there is also rotational vector acting in the direction of rotation which is a function of

CF Force = mass* radius*spin rate squared.

this second vector is what causes your bullets to blow-up when they are overstabilized. Just as you described velocity dominating over mass, so does RPM in the rotational force. These forces are gigantic!

All these forces work together. I just want to understand how each is contributing...again just for fun and I’m a glutton for punishment!

 

[AllThingsAI]

One more fun post to help everyone visualize this, then I’m off to test. Please watch the CD rotation video I posted first because I’ll use that for reference...otherwise you're going to think I sniff too much paint!

My final masterpiece:
That CD, in the video, is spinning on a spindle (Not moving forward) speeding up its rotation until it gets to a threshold of approx 28,000 RPMs....then BOOM it explodes so fast they can barely capture it with a crazy fast camera.

Take that same CD spinning at 27,000 rpm and move it forward at 4000fps (pick a speed, it doesn’t matter) that CD has crazy rotational forces acting on it, it’s locked and loaded, it has a hair trigger, and it’s ready to party like it’s 1999. It doesn’t matter how far forward it moves or how many times it spins over a distance, it’s angry and is on the verge of explosion if anything even touches it!

Now take that same Tasmanian Devil of a Spinning CD moving forwarded like a scalded cat in a mouse trap factory (4000fps), It now also has enough forward Moving kinetic energy to kill a moose! Shoot it into a prairie dog and Boom the CD breaks apart and flys out radially (CF force) and all the pieces continue forward at 4000fps dividing up all the forward kinetic energy amongst them...like a 12 gauge shotgun spreading out #2 lead shot.

Now what happens if the CD is only spinning at 14,000rpm? It’s tired and just wants to go to bed, not much rotational energy any more (it has low T). But it can still sprint forward like a scooter on a fresh charge (4000fps). What happens when it hits that same poor prairie dog? The bullet doesn’t break up radially like it did when it was younger and all it’s parts just can’t...well you know. (4x less potent). So all the fragments are grouped tighter together and turn That plagueless, beautiful, little prairie dog into a mere shell of its former self.

So which CD “hits” harder....hmmm

PS. A High velocity bullet spins 200,000-300,000RPM

This video is great too.

 

[markT]

I’ll throw this in the mix. Watch this one.