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300 Win Mag Questions?
Discussion regarding the reloading of ammunition and tuning of loads for accuracy
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chambered221
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PostPosted: Tue Oct 21, 2014 9:11 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Hey all ….... been a while !!! Howdy

The problem with discussions on twist rates, as it relates to expansion, usually involves different sides actually talking about different things.
Twist rate does not effect expansion. It can however affect the terminal results. This is why some argue that a faster twist will affect expansion. If a bullet spins faster as it travels through the wound channel the more opportunity it has to do damage.
Keep in mind we are talking about controlled expansion. The pink mist Elvis refers to is actually a bullet designed to explode, it's not an expanding bullet.



Slim, you seem to be a little confusing to me, in one statement you say twist has nothing to do with it.
Later you state your evidence is leaning toward maybe it does.
My first question would be how are you arriving at your down range velocities ???


Keep those test a coming....... maybe one of these days you'll convince me to give up my B-Tips Shocked

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Bushmaster
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PostPosted: Tue Oct 21, 2014 9:23 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

That's easy...Quit buying them.

Welcome back.

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slimjim
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PostPosted: Tue Oct 21, 2014 9:50 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

chambered, good to hear from you. I've tested enough to know that twist rate, more specifically RPM (twist rate + velocity), does affect bullet expansion - how much the bullet increases in diameter. I'm still trying to firgure out the why's and some of the when's. See if this explaination makes sense. If a bullet has enough RPM to stay stable in air, it will become unstable penetrating tissue if its shape remains unchanged. This goes for any bullet, lead-core or monolithic. That is because tissue is a denser medium than air. To stay stable in tissue, the bullet must have a much higher rotation rate (which can not be changed) or be shorter and larger diameter which is what happens to a bullet when it expands, i.e., its half its length and twice its diameter which is a tremendous increase in stability. It takes work (energy) and time for the bullet to transform to shorter and fatter. The bullet needs to have enough initial stability (RPM) to make it through this transition. If not, the bullet tumbles which stops the expansion proccess.

I've seen this mostly with TTSX bullets because they do not expand to as large a diameter as their TSX counterparts.

Like I said, I'm still testing and gathering evidence

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Bushmaster
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PostPosted: Tue Oct 21, 2014 11:31 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

I've been reading all of these posts. To some point I have to agree to disagree.

Due to the distance traveled by a bullet in one revolution I can not see where there is enough centrifical force to effect bullet expantion. Especially when it has entered the body. The bullet is slowed so fast that centrifical force would be negligable. Expantion is more of a hydraulic force then centrifical. Centrifical force may be a factor, but of little or no effect.

Just my opinion (feeling) on the subject

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Pumpkinslinger
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PostPosted: Tue Oct 21, 2014 12:00 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

IMO the only way to see if RPM, or twist rate, makes any difference would be to shoot a test with a specific bullet fired several times at the same velocity from two guns with different twists. If you just fire the bullet at different velocities from the same gun then the kinetic energy is what is making the difference.

I'm with Bushy on this one, I don't think it would make much difference.

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MacD
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PostPosted: Tue Oct 21, 2014 12:46 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

A .308 with a twist rate of 1-12 spins a bullet with a muzzle velocity of 2800 fps at 168,000 RPM. Now when that bullet hits flesh and bone it has to slow down. IMO the more braking action the greater the stress on the bullet, the more this adds to expansion. I am guessing that lead core jacketed bullets with soft noses and/or perhaps round or flattened ones are most likely to be affected by this as the face of the bullet is experiencing the most friction as it expands. This is just my thoughts and not based on any research or reading beyond a few articles on twist rates that casually mention a relationship of speed and twist on terminal performance without expanding on these statements. Having said this I doubt spin rate has a lot of affect.

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chambered221
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PostPosted: Tue Oct 21, 2014 3:11 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

Perhaps asking the question as to when expansion occurs might help !!!

From everything I’ve ever read or seen a bullets expansion happens upon impact. It’s done expanding within the first inch or so of travel. That being the case the bullet is only rotating a fraction of a turn during the expansion process.
Whether or not it stays stable is irrelevant to this particular discussion, that’s a different discussion altogether.

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slimjim
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PostPosted: Tue Oct 21, 2014 7:19 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

I'm not doing a very good job of explaining the situation. Which is good because it helps improve my abilities to answer and address the situation.

chambered221 wrote:
Whether or not it stays stable is irrelevant to this particular discussion, that’s a different discussion altogether.

chambered, sorry, I have test data to the contrary. I've shot 150 TSXs in my .277 that were stable in flight. They shot 1" groups at 250 yards and punched paper just fine. However, the instant the nose touched the water jug I use in my terminal testing set-up, it keyholed on the front surface (tested 3 times). It didn't have enough rotation to stay stable enough to allow the impact force to open the bullet up/expand it. I don't have a gun with enough twist to increase its stability further but I have shot the same caliber TSX bullets that have the exact same expansion cavity just shorter (more stable) and they expand very well.

I have .277 110 and 130 TTSX that impact at the same velocity and the ones fired from the .270 expand more than the 6.8. In the 110 TTSX situation, 245,000 rpm vs 167,000 rpm - that is a significant difference in stability. Using Miller's equation on JBM website; 2.231 vs 1.677.

These monolithic bullets will fully expand if stable within the first 1 to 2 inches of penitration (inside of the elk's on-side rib cage)

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PostPosted: Tue Oct 21, 2014 7:39 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

I think the only way we will ever prove anything is to fire the bullets from different twist barrels and into a proven test medium then record the effects/results using a high speed camera that can be slowed sufficiently to allow the bullet's movements/deformations to be seen.

Slim, your tests are brilliant mate, but I think the points bought out by others are plausible. Keep working at it mate...if nothing else we are getting a good insight into bullet performance.

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Elvis
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PostPosted: Tue Oct 21, 2014 10:13 pm    Post subject: Re: 300 Win Mag Questions? Reply with quote

why did they have issues with the swift using cup and core bullets if centrifugal force isnt the issue...the plurry things tear themselves apart if you drive them fast enough..I believe they tear apart from inside out eg the G forces are too much and they simply open up and pull apart. based on this theory any spinning projectile MUST have a hell of a lot of force trying to pull it apart outwards. look at a picture of one of those mono projectiles recovered out of game they twist like a outboard motors propellor..enough to make the star shape twisted..I believe if the rotation wasnt a factor they would be simply shaped as a cross.
some projectiles are not recommended above a certain speed as they will blow up on impact and wont preform well eg hornadies SPSX 3000fps max.
I loaded 45grn taipans in my .223 and they didnt exit a hare..they just vanished inside them wtf wtf yet put that same projectile in a hornet as they were made for and they would be great.

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slimjim
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PostPosted: Wed Oct 22, 2014 2:30 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Elvis, I will set-up some tests to quantify what you are saying. Since there is such a wide range of twist rates in the .223, I'll use that caliber. I'll have to think about what bullet to use, TSXs, TTSX, or GMX?

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slimjim
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PostPosted: Wed Oct 22, 2014 3:01 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Vince wrote:
I think the only way we will ever prove anything is to fire the bullets from different twist barrels and into a proven test medium then record the effects/results using a high speed camera

Ah, yes. The non-believers. Unless they can see it with there own eyes, they won't be conVINCEd. You've got me chuckling, mate. Yep, I've had several people tell me my testing methods are invalid because I don't use ballistic gelatin. I can tell a lot without having a high-speed camera but I'll have to think how I might be able to capture some.

I've done over 300 bullet tests in .223, .243, .277, and .308 (I probably should go back and count them). I've laid bullets side by side with those recovered from game at the same conditions and they match. My test procedures work best for monolithic bullets and are weakest with the softer lead-core bullets that don't fragment, e.g., Fusion, CoreLokt, HotCore, because they are soft enough to still deform going through in the phonebook resulting in odd mushroom shapes. Accubonds test well.

I don't need a high-speed camera to confirm a 150 TSX yawed on impact if it leaves a keyhole in the front surface of a water jug. Other interesting clues I've found during testing. OTM don't expand from the tip, they yaw then break in half or swap ends and penetrate tail first. I recover their tips still intact. I can tell that a lead-core fragmentation bullet ejected its core in the first few inches because the inside of the copper jacket will be covered in dust from the water blast washing up dirt off the ground which the jacket then flies through before it enters the bullet trap.

I hear you, Vince. I have to provide better evidence.

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Vince
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PostPosted: Wed Oct 22, 2014 3:29 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Slim the Tester wrote:
...Ah, yes. The non-believers. Unless they can see it with there own eyes, they won't be conVINCEd. You've got me chuckling, mate. Yep, I've had several people tell me my testing methods are invalid because I don't use ballistic gelatin. I can tell a lot without having a high-speed camera but I'll have to think how I might be able to capture some.

Laughing Not unconvinced mate, I just think that being able to see the forces and changes a bullet goes through on impact, regardless of what those changes may be (tumbling, breaking up, expanding etc) will give a better understanding of billet performance. As for using ballistic gelatin...it's one option, but so long as each bullet is tested in the same medium, that's all that matters for consistency. Good thing about gelatin is it's opaque and allows you to see the bullet inside.

At the end if the day mate, your testing is very exhaustive and the results you record, whilst totally not definitive, are brilliant. Keep at it mate, you are doing a great job and providing good useable information.

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chambered221
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PostPosted: Wed Oct 22, 2014 5:05 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Slim, I first understood the discussion as being more expansion would occur in a 10 twist vs 11 twist. Then I took for granted that expansion had already occurred and you were talking about staying stable within the wound channel.

I don't find your 150gr results surprising. Barnes recommends a 1-9.5 twist for the 150gr. Your guns are probably somewhere between 10-12.
Your obviously running on the edge of stability. Benchrest shooters often say that is were they find their best groups. Having in flight stability does not necessarily mean the bullet will perform correctly once it hits the intended target. Bullet makers don't make twist recommendations based solely on flight stability. The bullet needs to have enough stability to stay true upon hitting it's target and proceed in a somewhat straight path.
Once that occurs the bullets speed will determine the amount of expansion that takes place.



Quote::
I have .277 110 and 130 TTSX that impact at the same velocity and the ones fired from the .270 expand more than the 6.8.

Again I'll ask...... how are you determining down range velocities ???

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chambered221
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PostPosted: Wed Oct 22, 2014 5:22 am    Post subject: Re: 300 Win Mag Questions? Reply with quote

Elvis, What you're referring to is an issue of bullet construction !!!
Those varmint bullets are made to disintegrate not expand. The faster they go the more violent they become.
Put those SX's through a swift at top speed and they'll disappear into a puff of smoke in flight.

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