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Rifle Bullet Performance
Discussions related to Guns and Firearms
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fnuser
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PostPosted: Mon Nov 30, 2009 8:26 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

a mushroomed shape also provide greater torque farther from the center axis. in a homogenous medium this doesn't mean much but the inside of anything big enough to call meat isn't. The problem of straight path inside the animal has already been solved for the animals that require it. i.e. cape buffalo, elephant, hippo, ya know stuff that stomps ya. The .270 Win is already quite a penetrator in deer I've recovered several bullets at the opposite end of the animal they were shot into front to back and visa-versa. and for a broadside shot you had better be very certain what's on the other side cause its gonna get hit.

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Pumpkinslinger
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PostPosted: Mon Nov 30, 2009 9:30 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

Slimjim, regarding the 30+ times faster twist; that is Rinker's number from the book and he shows you how to do the math to prove it. It is all about the density of the material the bullet is traveling through.

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slimjim
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PostPosted: Mon Nov 30, 2009 10:00 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

You guys are great! So much sharing of information, I can't even get my next post researched and written before more arrive. I love it!

I expected that the 30x factor had to be due to density of the material.
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slimjim
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PostPosted: Mon Nov 30, 2009 10:28 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

fnuser wrote:
a 1-8" .280 ackley designed around the 180 berger vld


I tried to look at an example in the GSC technical section to compare
twist rates. However, the 180gr VLD is 1.525 long and GSC doesn't make a .284 bullet that long (their longest is 1.44"), thus can't compare the difference in spin rate in GSC's "New Ruler".

I did find an example in .270 which typically has a 1:10 twist. the GSC 130gr HV bullet (1.29") is close to the same length as the Barnes 130gr TSX (1.302") and the Berger 150gr VLD (1.310). In this situation, GSC recommends a twist rate of 1:8.5 or faster for optimum terminal performance out to 500 yards and 1:8 to 1:7 for close in hunting in the bush. I have to use a shorter bullet to meet their recommendations. In my situation that is the Barnes 110gr TTSX (1.175").

Another example would be theGSC .308 177gr HV bullet (1.58"). This is 1/10th inch longer than the Berger 210gr VLD (1.490"). GSC recommends a twist rate of 1:9 or faster for optimum terminal performance out to 500 yards and 1:8.5 to 1:7 for close in hunting in the bush. I haven't heard of .30 cal twist rates that fast.
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Aloysius
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PostPosted: Tue Dec 01, 2009 4:03 am    Post subject: Re: Rifle Bullet Performance Reply with quote

Maybe they can produce custombarrels with that fast twist in SA?
I'm beginning to get some feeling about twist and in my opinion, the faster the better. When a twist is too fast for a certain bullet, one can easely take the speed down till that light bullet also gets stabilized. On the other hand: when a twist is too slow, maximum pressure will limit you when you want to increase the speed of that heavier (or longer) bullet till it stabilizes.

Makes sence?
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slimjim
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PostPosted: Tue Dec 01, 2009 7:01 am    Post subject: Re: Rifle Bullet Performance Reply with quote

Aloysius wrote:
Maybe they can produce custombarrels with that fast twist in SA?

You can get the barrels custom made here in the US. The fast twist, if you use modern bullets, is making sense to me. However, if you get a custom gun made like this it may be only good for one or two bullets. If it doesn't shoot like you want, you will have to go through the expense of getting a new barrel.

Also, most of their recommendations did not have an upper limit to twist but some bullets did for specific applications. All had a upper limit to twist for ranges beyond 500 yards/meters.
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Aloysius
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PostPosted: Tue Dec 01, 2009 7:32 am    Post subject: Re: Rifle Bullet Performance Reply with quote

Do you know the german Lutz Möller?
saxtech.eu/Hauptplatz.html
I have been told he 'invented' a special barrel with varrying twist. In my opinion this is something like the very expensive black powder match pistols, but for the high pressure modern amno. It seems his barrels had very high accuracy, but I think (and I'm not sure) he sold his patent to the military.

I don't know what you can or are alowed to do overthere, nor what kind of budget you can spend to experimental things, but maybe it gives you new ideas about things one thinks everything already have been tested.


Note: when you don't understand german, call Google Smile
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slimjim
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PostPosted: Tue Dec 01, 2009 10:14 am    Post subject: Re: Rifle Bullet Performance Reply with quote

Aloysius wrote:
Do you know the german Lutz Möller?
saxtech.eu/Hauptplatz.html

Aloysius, this is a great find of information. It will take me a couple of days to sift through it. I like what I initially see. Thanks!!
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Pumpkinslinger
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PostPosted: Tue Dec 01, 2009 10:43 am    Post subject: Re: Rifle Bullet Performance Reply with quote

Progressive twist, or "gain twist" barrels have been around since the 1800s. As I understand it the main problem is expense of manufacture and there can be some issues with long bullets.

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Aloysius
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PostPosted: Tue Dec 01, 2009 11:22 am    Post subject: Re: Rifle Bullet Performance Reply with quote

That's the nice thing about the internet. One comes in contact with a lot of "nuts" all around the world, but you have to use your own head to mix all info into something that could serve you or brings you the right idea Smile

be glad your government still alows you to do some experiments on this subject. In some parts of the world it's dangerous just to make a drawing on this subject without properly being licenced...
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slimjim
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PostPosted: Tue Dec 01, 2009 1:04 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

Aloysius wrote:
be glad your government still allows you to do some experiments on this subject. In some parts of the world it's dangerous just to make a drawing on this subject without properly being licenced...

Thanks for reminding us that we shouldn't take our freedom for granted!
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Elvis
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PostPosted: Tue Dec 01, 2009 1:42 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

I have read two articles here in NZ about these gs projectiles and they do sound great. the latest nz guns and hunting #115 has a article on the 110 270 and 280 most interesting. as for reinventing the wheel way back in 1900 and nuts and bolts I got a remington sportsman magazine which had a article on 12ga sabot loads which were solid copper with a hollow nose and 4 splits at the front. the gaf was when they hit the spin givin to the projectile made the pettles flare outwards like a outbourd propeller and they broke off going in different directions with the main piece or base if you like carrying on through. sound familiar??? lots of photos of what they did were with it and they shot real tight groups with a rifled barrel better than some centrefire rifles I have used. I think the concept is great but the price is prohibitave for this family man.I will be sticking to my 130grn taipans for the open and 150grn speer grand slams for the bush in my 270.

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slimjim
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PostPosted: Tue Dec 01, 2009 3:03 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

Interesting article Elvis. I thought rifled shotgun barrels were rather a modern adaptation.

Regarding cost, the GSC bullets are expensive to begin with and when you add in shipping the bullets better be a signficant advantage. I share your description of "prohibited". I don't know if its easy to get Barnes bullets but here in the US they are slightly more expensive than most premium bullets but not prohibitive. Comparing bullet for bullet between GSC and Barnes, GSC doesn't have much of a BC advantage in their hunting bullets except for the 177 gr .308 at .638 BC This is a pretty awesome BC for a hunting bullet but you would have to make a special barrel to get the twist high enough to use it. Thus, even though the GCS bullets may be better than Barnes, for the price, Barnes offers the advantage I think I'm looking for.


Last edited by slimjim on Tue Dec 01, 2009 3:21 pm; edited 1 time in total
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slimjim
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PostPosted: Tue Dec 01, 2009 3:18 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

Aloysius wrote:
Do you know the german Lutz Möller (LM)?
saxtech.eu/Hauptplatz.html

Note: when you don't understand german, call Google :)

Thanks for the tip on Google's translator! I didn't know that was there.

This is an interesting site with interesting LM bullets. I haven't gotten it all translated but his bullets are lighter than most, e.g., 95 grain for the 270 vs 110gr for the light weight Barnes I'm currently shooting. They are achieving another 150 to 200 fps than my load but it is a lighter grain bullet. It looks like lots of people use the .308. Its velocities are the same as I was getting with my .308 130gr Barnes TTSX.

The LM bullets are designed not to mushroom but loose their large ballistic tip and present a flat frontal area. GCS suggests that this the best shape to default to if the pedals break off the mushroom and still have an effective wound channel.
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Dimitri
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PostPosted: Tue Dec 01, 2009 5:19 pm    Post subject: Re: Rifle Bullet Performance Reply with quote

Twist rate should be to stablize the ammunition while going through the air. Then we should be using more "improved" ammunition designs. One design I always liked but impractical (and illegal for hunting) is the way the British made their 303British FMJ with a aluminum tip infront of the lead. This caused them to destabilize once they hit the target and worked well for moose hunting up here with surplus ammunition for years.

Dimitri

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