Rifle Bullet Performance

slimjim · Posted: Sat Nov 28, 2009 9:49 pm Post subject: Rifle Bullet Performance

GS Custom Bullets FAQ

I've found this website from GS Custom Bullets in South Africa. It has a wealth information on bullets and their performance. Much of it is unconventional and backed with lots of terminal performance on various game animals. They recommend lighter bullets launched at higher speeds. I have already made the "transition" to lighter, higher speed bullets with Barnes' all-copper banded bullets. What I found particularly interesting on this website was their discussion of twist rate. They promote the need for higher spin rates than is required to stabilize the bullet in flight. I had to read it a couple of times for it to sink in. GSC's position is for a bullet to stay stable upon game entry (terminal phase), spin rates must be faster/higher. They say the wound channel is more predictable, straighter, and lethal and results in less meat damage. An article in AR Rifleman Magizine Winter 2010 (pg 105) by Gary Cook "Extreme Range Spin Zone" states he has also experienced the increased lethality with higher spin rates. This gives me more confidence in my choice to switch to a 110gr Barnes TTSX launched at 3400 fps in my .270 Win for deer.

chambered221 · Posted: Sat Nov 28, 2009 11:07 pm Post subject: Re: Rifle Bullet Performance

I wouldn't necessarily consider their stance unconventional !!!

The problem with ballistics (internal,exterior, or terminal) in general was the fact that a lot of what we grew up thinking was fact was more of what people thought and believed.
Today we have better equipment and knowledge that has proven and dispelled the conjecture.
Twist rates being one of the biggest. Back when all bullets were made somewhat the same way weight was a reliable judge. Not so today with the different metals and the more streamline ogives that lengthens and changes the balance.

Definitely good info !!! Thanks for the post !!!

Pumpkinslinger · Posted: Sat Nov 28, 2009 11:33 pm Post subject: Re: Rifle Bullet Performance

Remember that the old Greenhill formula (from 1879) is based on bullet LENGTH, not weight.

I noticed that Wikipedia has an article on the subject of twist rate and in it they said that higher bullet RPMs reduce "destructive power" because more of the energy is used for rotational KE (spinning) instead of linear KE (making a hole). Unfortunately they don't give a source for that info. Makes some sense but I bet a critter couldn't tell.

en.wikipedia.org/wiki/Rifling

Aloysius · Posted: Sun Nov 29, 2009 12:20 pm Post subject: Re: Rifle Bullet Performance

And no doubt, Gerard (the "G" in "GS" or is it Gina now?) certainly knows what he's saying. I always read everything Gerard is saying on the RASA-forum with special interests. Some think they know all by reading or studying, in my opinion Gerard knows everything by experience...
And SA is a land full of big animals and large distances, that's where you can see a bullet realy work.

slimjim · Posted: Sun Nov 29, 2009 2:36 pm Post subject: Re: Rifle Bullet Performance

Pumpkinslinger wrote:

higher bullet RPMs reduce "destructive power" because more of the energy is used for rotational KE (spinning) instead of linear KE (making a hole). Unfortunately they don't give a source for that info.

This is the first I've heard this theory. I haven't seen any energy equations that use twist rate as a factor.

slimjim · Posted: Sun Nov 29, 2009 2:56 pm Post subject: Re: Rifle Bullet Performance

Aloysius wrote:

I always read everything Gerard is saying on the RASA-forum with special interests.

I was unable to locate this forum. Do you have a web address you could provide?

Aloysius · Posted: Sun Nov 29, 2009 3:26 pm Post subject: Re: Rifle Bullet Performance

at your service Smile

www.reloadsa.co.za/Mem.../index.php

Maybe you have to register and when the link shouldn't work for you, use only
www.reloadsa.co.za
and go then to the forum.

chambered221 · Posted: Sun Nov 29, 2009 6:50 pm Post subject: Re: Rifle Bullet Performance

slimjim wrote:

Pumpkinslinger wrote:

higher bullet RPMs reduce "destructive power" because more of the energy is used for rotational KE (spinning) instead of linear KE (making a hole). Unfortunately they don't give a source for that info.

This is the first I've heard this theory. I haven't seen any energy equations that use twist rate as a factor.

Robert Rinker covers this very briefly in his book !!!

The basis of the theory is true but only accounts for about 1% or less of the available energy as a general rule. He shows the math to prove it in the book if you are interested.

Pumpkinslinger · Posted: Sun Nov 29, 2009 10:01 pm Post subject: Re: Rifle Bullet Performance

Thanks Chambered! Isn't that a great book for shooters? I figured it couldn't make a whole lot of difference unless you made LARGE changes in twist rate and bullet RPM.

Pumpkinslinger · Posted: Mon Nov 30, 2009 9:40 am Post subject: Re: Rifle Bullet Performance

Chambered, I reread Rinker and of course you're correct. No matter how you want to look at it (energy of spin taking up part of the total available energy from the powder charge OR energy of spin adding to the terminal effect) the rotational energy is 1% or less of the total. I also noted that, in order to make the bullet more stable in a critter (mostly water) the twist rate would have to be 30+ times faster.

chambered221 · Posted: Mon Nov 30, 2009 6:57 pm Post subject: Re: Rifle Bullet Performance

Pumpkinslinger wrote:

Thanks Chambered! Isn't that a great book for shooters?

Yes it is......a must read for anyone with even the slightest interested in ballistics !!!

slimjim · Posted: Mon Nov 30, 2009 7:32 pm Post subject: Re: Rifle Bullet Performance

Pumpkinslinger wrote:

in order to make the bullet more stable in a critter (mostly water) the twist rate would have to be 30+ times faster.

30 times faster seems a bit much. Glock 9mm can shoot round nose bullets underwater with the same twist rate as in the air. The bullets don't go very far because of the water's density. If twist rate had to be 30 times more it doesn't seem logical a Glock could do this.

WHAT ABOUT MEAT DAMAGE?

This section from GS Custom Bullets addresses the issue of meat damage and points out two aspects that increased meat damage; Bullet Fragmentation and Bullet Instability (tumbling). Legacy lead-core bullets driven at too high a velocity or spin rate can fragment. Solid copper bullets can take the speed and higher spin rate and still maintain integrity. Bullets at too low a spin rate can tumble. GS recommends a spin rate that is almost 50% faster than their long-range spin rate for hunting dangerous game or in thick brush. About 30% faster for game inside of 500 yards. You can see this in their recommended twist rate for each bullet in their technical section.

.270 110gr

I've listed the .270 110gr bullet as an example above. A 1:10 twist satisfies their requirements. Below is the link to the 120gr bullet:

.270 120gr

This bullet is 0.1 inches longer and a 1:10 twist is only recommended for engaging game outside of 500 yards and would be the minimum. From what I understand, outside of 500 yards, twist is a compromise. Spinning faster is better for terminal performance but maybe too fast for the bullet to nose over on the backside of the trajectory curve which would cause the bullet to impact nose up instead of dead-on its trajectory path.

fnuser · Posted: Mon Nov 30, 2009 7:49 pm Post subject: Re: Rifle Bullet Performance

actually the shape of the bullet has more to do with its stability then any of the spin the farther forward the center of gravity in any particular bullet the more stable it will remain upon entrance this has been demonstrated to death by the u.s. government at the goat labs where various spitzer and round nose bullets have been x-rayed in goat carcasses imagin the bullet striking anything partially yawed the center of gravity will follow the path of least resistance and the spitzer shape bullet will begin to de-stabilize and rotate toward the front actually overcorrecting if it stays in the medium long enough.Fred N. Barnes ofGrand Junction CO experimented with several quick twist cartridges that had 1-5 twists using 200 g bullets in 6.5 caliber, he stated that any twist faster then this with conventional bullets at high velocity would pull them apart with centrifical force and 1-7 twist in the .257 caliber using 160g bullets was the object of a Dr.Ramon Samovia of Hollister CA, Both of these were conducted prior to the printing of Ackley's Handbook for Shooters and Reloaders volume 1 printed in 1962. Didn't mean to rain on your parade but as King Soloman said "There's nothing new under the Sun." They too were in search of free energy and lethality. Almost everything I've shot in the last 20 years probably soaked up enough energy to kill it two or three times anyway so how dead is dead enough? This is the object of alot of discussion and may be for generations and although I myself have wildcatted several cartridges mostly for my own entertainment. and to fit in this action or to shoot this bullet at this velocity. I have to say with the plethora of cartridges that are available today it's getting harder and harder to re-invent the wheel. Whenever I contact a reamer manufacturer like Dave Kiff or somebody like this that has seen thousands of cartidge sketchs invaribly he will state he has this already made up give or take .002" here and there would that one be okay? This is extremely frustrating for somebody like myself and maybe one who reads this that is trying so hard to be revolutionary with the latest greatest mousetrap. Thanks for the topic.

slimjim · Posted: Mon Nov 30, 2009 8:09 pm Post subject: Re: Rifle Bullet Performance

fnuser wrote:

these were conducted prior to the printing of Ackley's Handbook for Shooters and Reloaders volume 1 printed in 1962. Didn't mean to rain on your parade but as King Soloman said "There's nothing new under the Sun."

I like a good discussion and am glad this topic is generating one. Can't be anything new since 1962? GS Custom in proposing the "New Rule" but it only applies with new monolithic bullets that can maintain integrity. I understand the nothing new with brass cartridges and how every case under the sun has been tried already. I believe its not the case that matters most - It's the bullet. Bullets have changed and most of that has been coming to focus in the last 5 to 10 years.

Also, a bullet that maintains its mushroom has a significant change in forward CG.

fnuser · Posted: Mon Nov 30, 2009 8:15 pm Post subject: Re: Rifle Bullet Performance

Actually long range shooting is where you find most of the quicker twist stuff "flying around" I just built a 1-8" .280 ackley designed around the 180 berger vld. I'm not the first to do this and alot of 1000 yard f-classers are now shooting this and other versions in the .284 win and similiar cartridges. I was interested in a "heavy" beanfielder. and decided to work around some proven data borrowed from the benchrest crowd.