470 Mbogo,
How do you take into consideration the fact that starting the bullets off at different velocities from the same twist barrel will alter the RPM's of the bullets? Just ignore it? Consider it to be insignificant? You would have to have a different twist rate barrel for each muzzle velocity to make each bullet arrive with the same velocity and spin rate.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

[QUOTE]Originally posted by Norbert:
Norbert,
I'd love to test a whole bunch but some things here are hard to get and we have that funny dollar. A company e-mailed me about their solids so I'll send them an e-mail and try them along with the Barnes and Woodleigh's. I'm out of Trophy Bonded Sledgehammers.

A worthwhile experiment would be to test a bullet's penetration (no mixing of Woodleighs in with the Barnes) at a fixed muzzle velocity and impact range but varying the barrel twist and hence RPM's. This would not be for any accuracy considerations but just to see if faster spin does increase penetration as claimed by many such as Ross Seyfried and Art Alphin. I have not read the book "Bullet Penetration" by MacPherson yet, but will eventually. I could start by looking in there. I suspect I will find supporting data there. Anyone else read this?

I am amused by all the disparagement of the .50 cals shooting 535 grain bullets. The proper hunting bullet weight is 570 to 600 grains for the .505 and .510 bores. These bullets moving at 2400 to 2500 fps will beat just about anything. However, some folks can't handle the heat so they stay out of the kitchen.

Comparing any bullet from .416 to .585 caliber in varying twists such as 1 in 10" to 1 in 18" would be very interesting. Then an accuracy test at 200 yards and 50 yards would help pick the right twist to compromise between penetration and accuracy with the 570 or 600 grain bullet.

I may have to do this myself. Let's see, a .510 JAB with a 1 in 14" twist to compare to the 1 in 10" that I already have...

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

Ron,

All in the name of science ;-) And what better excuse for a new rifle? So are you planning any other trips through town? Someday I'll have my 500, maybe in the fall.

Hey Paul H,
Good to talk to you again. You and Mitch are my only two real life contacts from this website, a pleasure in both cases. Of course I will be heading up to Alaska again, can't stay away from God's country. I will give you a call when I get there, maybe in September.....Moose season! Well, is a guide going to be required for a nonresident this year?

BTW, what twist rate is your .510 caliber barrel? If it is different than my 1 in 10" maybe I can bring my .510 JAB and knock over a moose with it then go to the range with some 3/4" plywood stacks for comparing the Jeffery to the JAB. We could do that individually at our own homes if we loaded the bullets to the same velocity. Please say you have a 1 in 12" or 1 in 14". If not, I believe Mitch has a 1 in 12" .500 A2.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

RAB,
good idea to do more tests on the twist problem. I think significant numbers you will only get with rather long bullets, therefore it is best done with heavy monolithics. And what about the distance? You have to know, when the bullet is going "asleep". Anyway, you have more than one effect or mechanism affecting penetration by the twist rate.

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I think that this experiment needs to be done on real game under field conditions top be meaningful.

Anybody want to subsidize a two year hunting trip?

Don

Ron,

My smith has the barrel and action, as I recall its either 1-14 or 1-15, its a douglas blank. I really want to try the 570 gr XLC, I figure at 2400 fps, it will be most impressive. I am concerned about the petals shedding though. I also agree that for the 50 to do its thing, it needs a 570, or better yet 600 gr slug.

I'll also be doing plenty of playing with cast bullets, I got an LBT 450 gr LFN gc mold, and plan to duplicate the 50 Alaskan, pushing 450's 2000 fps.

Paul,

Where can you get the LBT molds? I thought they were out of business. I'd like to get a 375 grain .416 LFN (.280 meplat).

Don

Norbert,
What are the mechanisms by which the twist affects penetration?
The monometal bullet is what I had in mind too: the 570 GS Custom FN and the Barnes solid, and why not throw in the Woodleighs too?
Wouldn't 50 yards be adequate for the penetration test, and 200 yards for the accuracy test?

Paul H,
Great! We could both load the same bullets to the same MV in the 2 different twist rates, my 10 and your 14/15, then build matching penetration boxes and see if the twist rate makes much difference. Trying the solids and X-Bullets of 570 grains seems to be in order for comparison.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

Don,

You're correct, LBT is no more. There are still used molds floating around. My buddy was getting some molds for his 500 Linebaugh, and came across the 450 gc mold, and I said to get it for me. It was a pretty good by for a used LBT, $50, though it was well used.

Cast Performance Bullets sells molds made by Balisticast, they are LBT style, cherry cut and cast iron, kinda steep at $95 for 2 cavity, but a nice mold. Another option is NEI, third option is Applegate.

Ron,

That ought to keep me busy this winter, or whenever I get it. I'm kinda tempted to start asking/bugging my smith, but I don't have the funds for the dies, stock, etc needed to finish the project.

Gents,
With regards to the ultimate penetration question,for equal muzzle energy in a calibre, wouldn't these bullet/twist combos that do not provide as much penetration then be depositing more energy in the animal?

I look forward to trying some tests(or seeing someone else do it) with a hot 585, tight twist, and the woodleigh solids.

The 585 woodleighs are probably the 'pointiest' solids I've ever seen.

Karl.

Karl,
Good point, and a desirable thing if ultimate penetration is not the goal.

Paul H,
One of these days you'll get it ready. My work and travel schedule impairs me too. I have an AR-50 with a 15 twist barrel. I could load a 50 BMG round down to 2400 fps with the hunting bullets and try those, for the twist versus penetration test.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

RAB,

we are going in a rather complex matter which is not very important for the average hunter.
But in short, if you want to study the effect of twist on penetration, you should use bullets which show the same stability factor for a given twist. That means equal lenght of longer bullets, e.g. monolithics. If you throw in the short Woodleighs, the stability factor is different and gives an additional variability.
The gyroscopic stability, given by the twist rate, is damping after leaving the muzzle at least three initial deviations: a set off of the bullets center of gravity from the ideal path, resulting in a "corkscrew" motion (caused by mechanical irregularities of the bullet and/or barrel). A yaw around the COG of some degrees angle, "precession" (because the air forces are acting on a point at a distance in front of the COG). Last a small circular movement of the tip, called nutation.
These effects, before damped considerably, make the bullet susceptible to other forces generated at the impact on a target. For instance, a bullet normaly shows no influence of the angle of impact, but a finishing shot at a few inches often shows strange behaviour of its path or even tumbling. The angle of yaw can cause different drag forces. Normaly only the tip is exposed to it, but at an angle parts of the shank may come into play.
If you want to study the effects of the nose shape, cutting bands or the like on penetration, you must get rid of these effects and work at distances where the bullet has become "asleep". I can only guess that it may be at 20 or better 50 yards. It is more important the bigger the calibers are. I think those tests would give us valuable information. There is also a question to me, wether "shoulder stabilisation" is working or not.
A big problem is the choice of the target material. I use solids only on elephant heads at about 20 yards. Therefore my ultimate test is the ele head. To sort out at the range the best aequivalent to tissue is gelatine. But who of us amateur ballisticians can afford to use this? And it is not really a substitute for an ele head. Plywood also has its restrictions because it is only broken and sheared and has no fluid involved in the penetration mechanism. I use a kind of resin bonded kitchen board, 1.5". On impact this material smelts and flows like water in tissue around the bullet and may generate the "supercavitation" effect.

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Mbogo,
Very interresting stuff, I really enjoyed it...

I have played around with similar cartridges in the past such as the 475 Ackley, 475 A&M (Atkinson & Marquitte) and the 475 Barnes Supreme, I suppose thats why I have Bursitis in my neck and shoulder today...All mighty powerful rounds...

Norbert,
I follow you. What is a trade name or generic name for this resin bonded kitchen board? Something tougher and more plastic or fluid than plywood would be a good idea with the .510 bullets. This might even allow testing of the armor piercing bullets from a 10 twist and a 15 twist at the same velocity. Steel plate penetration might come into play there.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

[QUOTE]Originally posted by R. A. Berry:
R.A.Berry,
My main concern was to test the bullets at different yardages to see if there would be different depths of penetration due to better bullet stabilization. The rotational velocity is something out of my control because I only have the one 416 Rigby. My intention is to set my chronograph up in front of the target box to monitor the velocity at the point of impact. I was going to do this at point blank, 25 yds., 50 yds.,and 100 yds. with the Barnes Solids and then again with the Hornady 416 solids. This I think should move into some of the questions you were wondering about the same velocity with a higher rotational velocity. Because the velocity will drop off rapidly but the rotational velocity will only change slightly. As long as I can keep the velocity at impact as close as possible the biggest variance will be rotational velocity. Anyway we'll give it a try and see what results come out of it. What velocities were you looking to load the .510-600 grain bullets to? I think my 500 A-Square is a one in 12 twist but with the 23 inch barrel 2400 fps is about where it ends.
The 577 T-Rex of Mitch's that you did such a fine job with did it have the Answer recoil system and the muzzle brake that they do? I looked at one of A-Square's at the Safari Club Convention in 96 and it looked like a real Red Neck Run special. The Red Neck Run is a local Boxing Day bring out all the goodies,head up the mountain until stopped by snow, build the big fire, eat all makes of game sausage and Christmas goodies and have one hell of a big shoot off. It is possible to hit hand thrown clays with a Marlin 44 cal lever gun. I threw the clays.
Some other thoughts on the rotational velocity: With the actual time the bullet spends from the point of contact until it comes to rest(milliseconds) do you think the extra rotational velocity will matter? How many revolutions do think the bullet will actually make during the penetration of thirty-five or forty inches of plywood? How do you figure in the deceleration of the rotational velocity? By the time the bullet has travelled ten inches is there any difference in the rotational velocities or has the friction resulted in the two shots becoming so close in speed that it is no longer relevant. At what point are we picking fly crap out of pepper? I think the point that the bullet has stabalized in flight will be the most relevant. I'm picking up the plywood on Monday. I would like to thank Mike 375 for introducing me to this site and this forum. It's been most interesting with a lot of good discussion and ideas. 470 Mbogo

[This message has been edited by 470 Mbogo (edited 04-28-2001).]

470 Mbogo,
2400 fps would be perfect.
Mitch has the Answer System recoil pad, which I think works great and looks good too, aesthetically pleasing to my eye. His T. rex has a very efficient brake which is like a KDF with modifications such as bigger holes.
As for all the technical details...I don't know. I was hoping you could tell me! Is it real or insignificant, this twist versus penetration thing?

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

As to twist there must be some "real field evidence" as I notice American Hunting Rifles are using very quick twists. I think they are 1 in 12 for 50 which is very fast. Same pitch as 1 in 6 in 25 caliber.

However from a theorectical point of view one would think there should be no difference.

Certainly, the twist rate required when a projectile penetrates a medium denser than air is much faster. In other words, if we were shooting under water we would need much quicker twists in our rifles.

But whether the twist be 1 in 12 or 1 in 16 etc. it is far too slow for a bullet penetrating a medium denser than air.

I would see it being similar to shooting 200 grain spitzers from a 30 caliber at a 100 yard target with a 1 in 70 twist instead of a 1 in 100 twist.

Mike

Mike375,
I will do some tests of the 15 and 10 twists with the .510 bullets when I get the time to play. If anyone knows of some tests of penetration correlation with bullet RPM's it would be nice to hear.

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Good huntin' and shootin',
Bwanawannabe, Daktari Ron

Again:
A bullet under hunting conditions is not stabilized in the aqueous tissue as it is in air. It retains its movement ( evtl. yaw etc.) by inertia and is travelling in a vapor bubble, most of the bullet shank is not in contact with the tissue. The hydraulic wave, generated at the nose and cutting effects are responsible for the energy transfer.

Differences in penetration caused by the twist are only to expect with bullets of different lenght at close distances. For normal hunting distances this question is of no meaning. Exception: Dangerous game at close quarters.

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Norbert,

... and that's an intersting exception!
I'm rading this with great interest, I wish I knew the answers to all these questions.
Don

Don G,

most of the discrepancies in testing bullet behaviour are caused by the short distances the authors used.
See the recent experiments of Haley in the African Hunter 6/6 on .375 300 gr bullet performance. His conclusions are very right, but he didn�t say at what distance he performend the tests. All the possibilities of misleading results he mentioned are from the influence on the yaw angle effective at close quarters.

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[QUOTE]Originally posted by Norbert

Hi Gentelmen,

I picked up the plywood,cut it up and did the shooting today. It took a while and a couple of trips to the range to get the loads for the correct velocities at the tested ranges. I shot the test box which had 11.5 by 11.5 squares of 3/4 plywood stacked like a loaf of bread as described by George Hoffman, to a depth of 60 inches. I shot the box at 50 yds, 25 yds and at point blank (six inches). I set the chronograph up directly in front of the test box to record the velocities at the point of impact. I also shot 3 shots from 100 yds at a velocity of 2500 fps which resulted in 2260-2277 fps at the point of impact. All bullets were Barnes solids weighing 400 grains. The results were the three bullets shot from 100 yds. were recovered at 29 inches all in the same piece of plywood. The shots from 50yds, 25yds, and point blank were recovered in the same piece of plywood at 34 inches. There were three shots from 50 yds one from 25 yds and one from point blank. The velocities at the point of impact ranged from 2380 fps.-2408 fps. There is not more than 1 inch difference between the four shots. This would indicate that all the above theories are just that. I know this is not the same thing as testing on animals but these are the results. I'll post pictures etc. on my website along with the information gathered in the near future. 470 Mbogo

Mbogo,

A whole lot of work with very interesting results. What was the penetration on the nearer shots? More than 34 inches?

Don

[QUOTE]Originally posted by Don
Hi Don,

The plywood piece at the 34 inch mark has five bullets stuck in it.The one from twenty five yards has the base of the bullet flush with the plywood. The shot from point blank or six inches has the base of the bullet sticking out.5900 inches. The three shots from 50 yds. have the base of the bullet sticking out .4470, .5625 and.8905. So in five shots there is only .8905 difference in penetration from point blank, 25 yards and 50 yards. The difference in velocity at the point of impact for the five shots was 28 feet per second. 470 Mbogo