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I may have shit up my nose , perhaps in my mouth but last time I looked I do not believe that I have shit for brains.

So where are we at this point?

The consensus seems to be that angular velocity sets the bullet up for a specific impact yaw angle and that the size of that yaw angle determines in-target behavior.

Now from this the AR experts assume, and correct me if I’m wrong that based on observation a fast twist barrel will give better impact yaw angles than slower twist barrels based on observations of deeper penetration.

In fact across the board there are participants who routinely promote, de novo that fast twist barrels be used.

This then would imply that each and every gunbarrel maker that has ever built a barrel to what can be seen as “standard” or “CIP spec “ don’t know what they are doing and are idiots !

Lets look at this closely:

Why is it that the faster twist barrels consistently outpenetrate "traditional" and “CIP standard” slower twist barrels for the currently tested FN monometal bullets ?

The reason is because the faster twist barrels are actually the correct twist for these bullets.

The monometal FN made of copper or brass is consistently longer than a comparable weight lead and copper FMJ.

Based on the Gyro theorem, or it’s simplified and oft misapplied derivative the Greenhill formula we see that the correct twist for a monometal would have to be faster than that of a standard lead and copper FMJ or soft.

That means that "like weight" Monometal Solids are usually then understabilized when shot from standard barrels and thus have large yaw angles throughout the flight trajectory.

But this raises some interesting questions:

Does this apply if the shooter is to shoot a FN bullet made of copper and lead?

Will the fast twist still give smaller yaw and thus bigger penetration?

Or lets say we make our FN from a heavier metal than solid copper or brass ( copper clad tungsten) so that it’s length is the same as the old copper and lead bullet ?
Would the fast twist barrel now still give better penetration?


If say a 1: 10 barrel gives better penetration than say a standard 1:14 twist barrel for a monometal why not go 1:9 or even 1:7 ? because then you are going to get even better penetration ?????

Well not quite:

The Gyro theorem comes with caveats and an important caveat is the relationship of gyroscopic stability and the condition of tractability.

There is a direct inverse relationship between static stability and tractability.

If the angular velocity is too high the bullet becomes less tractable. Which implies that the bullets yaw angle increases. This in turn has a significant impact on in target stability and the wounding process. ( this is undisputed in the wound ballistics literature )

The bullet will sit at an angle to it’s direction of motion as it exits the barrel, they all do but because of the relative high ratio of its gyroscopic moment due to the high spin rate to the overturning moment, will keep this position and take longer to damp out slow arm gyratrion , it also does not cone out as much as a bullet that is shot from the correct twist barrel , in fact it gets worse downrage. ( True overtabilization does not really occur in flat fire trajectories but the yaw angle is none the less quite high)

The whole issue of yaw, stabililty and wounding capability is best illustrated and likely the best researched in the form of the M16 rifle and it’s variants and ammunition

The M16 and its ammo may very well be the most researched in this regard and serves as a very good example of my position on this in action.

The oiginal M16 was designed for the M193 bullet and was made with a 1:12 Barrel.

The vital stats for this bullet is:
Mass: 3.56gm
Length: 19mm
Ja: 1.165
Jq: 0.763
Distance nose to CG: 11.3mm

The original barrel twist calculated for these vitals called for a 1:12 twist barrel and extensive testing done comparing this to a 1:14 twist barrel showed that the 1:12 would give the best performance over the whole temperature and barometric spectrum called for in a battle rifle of this nature.

The launch and flight characteristics of the M193 bullet also showed the best overall results in terms of initial Yaw, coning and overall loss of velocity over distance when compared to the 1:14 twist.

What was noted on impact of the bullet in the bullet stop in the lab at Aberdeen was that often some the bullets fired from the 1:14 would not penetrate the water saturated foam used as a bullet trap at the end of the range.

But along came NATO and they chose a heavier bullet, the SS109:

The vitals for the SS109 is:
Mass: 4 gm
Length: 23.1mm
Ja: 1.096
Jq: 1.123
Distance nose to CG 14.5mm

This bullet does not stabilize in the 1: 12 inch barrel, just like the M193 in the 1:14

So NATO chose a 1:7 barrel.

The US is part of NATO and to appease the NATO STANAG regulations changed some M16’ models to 1:7 twists. The FN MINIMI and the US derivative of the MINIMI has two barrel twists, a 1:12 for the M193 bullet and a 1:7 for the SS109 bullet

This in practice meant that the 1:7 barrel should stabilize the SS109 bullet and would based on the commonly assumed AR expert standard even stabilize a M193 bullet better?
Right? ......Wrong !

The 1:7 overstabilizes the M193 bullet in as much as it leads to a larger Start yaw and the bullet remains at that large yaw way longer than when shot from a 1: 12 barrel and this lead to reports of bullet fragmentation at impact, something that was extensively researched and documented.

My point in all of this is:

Modern monometal solids are longer than their “ old” Lead and Copper FMJ’s .

Based on the gyro theorem old style FMJ ‘s and cup and core bullets are a best fit with “standrard CIP “ twist barrels.

When shooting modern monometals the barrel twist will have to adapted for by shooting faster twist barrels.
It means that if the new green bullet initiative takes hold organizations like CIP would have to revise their specs in terms of twist rates for cartridge. But it has a caveat if one chooses the fast twist barrel it may not be the best fit for old style bullets.



And just as a sidebar:

Starting yaw is not a fixed value, it is a random value within a lower and upper limit, it varies from shot to shot same rifle, shot to shot different rifles.

Distance to damping of nutation ( fast arm rotation) is random and may vary shot to shot same rifle, shot to shot different rifles even by as much as a feet and yards ! this was shown at Aberdeen and cited by two different testers)

Yaw measured at different points in a trajectory same thing, loss of velocity same thing all are random between an upper and lower limits.

Yaw is also temperature and barometric pressure sensitive again within a background of randomness.

So everything we see and assume has to be given the statistical treatment.


Intesresting reading:
Sturdivan LM, Bexon R: A unified yaw-penetration model for bullets. Aberdeen, Md ., U.S. Army Chemical Systems Laboratory, 1982

Larry Sturdivan was one of the expert witnesses that was called for the JFK assasination hearings, his testimony is public knowledge and can be googled. His explantions regarding yaw at these hearings are interesting and as Vapo pointed us to an article he found will fit perefectly Wink

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but last time I looked I do not believe that I have shit for brains.

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This then would imply that each and every gunbarrel maker that has ever built a barrel to what can be seen as “standard” or “CIP spec “ don’t know what they are doing and are idiots !

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Why is it that the faster twist barrels consistently outpenetrate "traditional" and “CIP standard” slower twist barrels for the currently tested FN monometal bullets ?

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The reason is because the faster twist barrels are actually the correct twist for these bullets.

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The monometal FN made of copper or brass is consistently longer than a comparable weight lead and copper FMJ.

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Based on the Gyro theorem, or it’s simplified and oft misapplied derivative the Greenhill formula we see that the correct twist for a monometal would have to be faster than that of a standard lead and copper FMJ or soft.

quote:

That means that "like weight" Monometal Solids are usually then understabilized when shot from standard barrels and thus have large yaw angles throughout the flight trajectory.

quote:

The Gyro theorem comes with caveats and an important caveat is the relationship of gyroscopic stability and the condition of tractability.

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There is a direct inverse relationship between static stability and tractability.

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If the angular velocity is too high the bullet becomes less tractable. Which implies that the bullets yaw angle increases. This in turn has a significant impact on in target stability and the wounding process. ( this is undisputed in the wound ballistics literature )

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Starting yaw is not a fixed value, it is a random value within a lower and upper limit, it varies from shot to shot same rifle, shot to shot different rifles.

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Distance to damping of nutation ( fast arm rotation) is random and may vary shot to shot same rifle, shot to shot different rifles even by as much as a feet and yards ! this was shown at Aberdeen and cited by two different testers)

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Yaw measured at different points in a trajectory same thing, loss of velocity same thing all are random between an upper and lower limits.

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I believe that a meplat of 78% in conjunction with a nose profile like the GS Custom wth sharp and not rounded shoulders will get the most penetration.

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Originally posted by someoldguy:


The meplat looks way small, I agree. I haven't measured any meplats, but I could understand the problem if you're using a caliper. The only thing I could think of sounds ridiculous. Take a dark crayon, some lipstick or something similar, cover the meplat surface with it, and daub the meplat on a clean piece of paper, being careful not to smudge it. Then you can measure your mark on the paper with the caliper. It probably won't be precise, but it would undoubtedly be less aggravation.

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Originally posted by Gerard:


[QUOTE] This then would imply that each and every gunbarrel maker that has ever built a barrel to what can be seen as “standard” or “CIP spec “ don’t know what they are doing and are idiots !

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Why is it that the faster twist barrels consistently outpenetrate "traditional" and “CIP standard” slower twist barrels for the currently tested FN monometal bullets ?

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The reason is because the faster twist barrels are actually the correct twist for these bullets.

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The monometal FN made of copper or brass is consistently longer than a comparable weight lead and copper FMJ.

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Originally posted by someoldguy:

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I believe that a meplat of 78% in conjunction with a nose profile like the GS Custom wth sharp and not rounded shoulders will get the most penetration.

Mainly because of the outstanding performance of the Woodleighs that we've all seen, I would agree that a 78 percent meplat is definitely still in the "Good Zone." But also more desirable for stability is the sharp shoulder instead of the rounded. So I could understand why such a bullet would be a great penetrator.

I'm beginning to come to the conclusion that the reason that rounded bullets in general aren't as stable as their "flatter" counterparts is mainly a matter of traction. (Think of a bad tire on wet pavement.)
But like so many of my conclusions in this field of study, this could change.

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Originally posted by ALF:

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your statement is refuted by recent tests conducted by Mike70560. The following sequence of quotations fully demonstrate that a modern FN monometal bullet outperform the traditional early 20th century FMJ bullet even when fired utilizing a traditional slow CIP standard twist rate…in this case a 1:20” twist rate in a double rifle

sadly and as much as I would like to conldude anything for that actual firing of only two shots and comparing we cannot deduct anything.

IN rder to prove at a trend many shots need to be taken just a Sturdivan, McCoy and Piddington all from Abrdeen have shown and secondly I am not convinced that the target as much as we try is actually uniform so we may deduct anything from it.

When we look a Youngs work on the determination on nose shape as a factor in peneration of materials we see tet went to great lengths to standardise on the targets used, in this case sand carfefully ,sifted,sorted weighed and wetted to a certain degree of water saturation

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The bullet is spinning inside a relative vacuum, not in a medium 1000 times denser than air.
Spin continues to steer the bullet inside the cavity, the sides of the bullet are not "wetted."
The FN bullet is much more effective at slamming the reactive (exponential-function-resistance) media aside.
A spinning bullet inside a cavity is clearly seen in many high speed films of transparent gelatin or water.
Google the Larry Sturdivan testimony at the JFK hearings, for his expert witness detailing descriptions of this.

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The spitzer bullets of the M16 yaw and tumble much more quickly inside the medium.

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

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Originally posted by someoldguy:

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What's Life Without a Little Fun?

Oh No, he is at it again

I know it's your ancestors, Dr M, but the one with the black hair reminds me of the lead guitarist in Thin Lizzy. Just a coincidence I guess.

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Regarding different meplats on modified Barnes RN monos:
Standard RN - 2' stable, 2' wild, gone before 5'
0.275" meplat - stable beyond 10', not recovered
0.325" meplat - stable beyond 9', recovered before 10'
0.375" meplat - stable beyond 7', recovered before 8'
0.448" meplat - stable beyond 6', recovered before 7'

These were all fired in a 1:14 twist .458Lott, approximately 480 grain projectiles, loaded to approximately 2200fps, from 30' above the surface of the water.

Thanks for sharing these test results!
FWIW, my penetration model didn't fare so well here with the water penetration.


Here are my predictions:

.275 meplat -- 11 feet (OK)
.325 " -- 8 feet (mkay)
.375 " -- 6 feet (somewhat off)
.448 " -- 4 feet (a good bit off)

Anyway, keep the tests comin', guys! My nipples are hard with expectation!

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

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No one wants to admit that the cavitation produced by the bullet nose slamming through the media produces a vacuum effect in the cavity around the bullet?
The bullet is spinning inside a relative vacuum, not in a medium 1000 times denser than air.

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With non deforming flat nose solids I think it needs a new SD category. Call it the Weight to meplat SD or WMSD.

If you have a 60% Meplat on a 480 grain .458 bullet making the frontal area (not the bullet diameter) of about .275"

This gives an ASTONISHING SD or WMSD of .907!!!!! talk about a WMD

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Originally posted by someoldguy:

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With non deforming flat nose solids I think it needs a new SD category. Call it the Weight to meplat SD or WMSD.

If you have a 60% Meplat on a 480 grain .458 bullet making the frontal area (not the bullet diameter) of about .275"

This gives an ASTONISHING SD or WMSD of .907!!!!! talk about a WMD

That's the assumption I've been using in my penetration formula, whenever the meplat is known. Trouble is, very small meplats don't behave in the way that they should in the real world. I'm sure Michael has observed this too, so he likes a meplat of no less than 65 percent of bullet diameter.
Much smaller meplats than the caliber "should" be able to penetrate extremely well, no doubt, but it would appear that their problem is stabilization.

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Originally posted by PWS:
The question was poised regarding modifying a old style RN mono.

I've tried this. My bullet test tube was a plywood baffled "ladder" that I was able to submerge in the North Pacific off the side of a large dock. The baffles were 24" square and staged at 12" intervals. I was then able to fire down into the fixture to record the bullet path in saltwater.

Discussion has also centered around relative meplat diameters. In my tests, those flats changed the bullet completely varying with the diameter of the flat. From a wild, unpredictable tumbler to a straight drilling projectile.




Bullets in the above photo:

1. standard Barnes RN Mono
2. #1 but with grooves to move CG forward of CF
3. #1 with FN and second crimp groove (0.325" meplat)
4. #1 with hemisphere completely removed (0.448" meplat)
5. self designed "super semiwadcutter" (0.325" meplat)
6. #5 with relief grooves.

My notes indicate:

1. Capable of penetrating 2' straight and stable, keyhole at 3', always deviates outside of 24"square before 5' of penetration
2. Completely unstable. Believe it's moreso an issue of poor engraving leading to large angle of attack. Nonetheless, weight forward did nothing beneficial in target as entry baffle recorded a round hole.
3. Penetrated straight beyond ninth baffle, recovered resting on tenth.
4. GEYSER upon firing, penetrated beyond sixth baffle, recovered on seventh
5. & 6. Multiple shots, recovered between ninth and tenth baffle, always straight, always stable


Regarding different meplats on modified Barnes RN monos:

Standard RN - 2' stable, 2' wild, gone before 5'
0.275" meplat - stable beyond 10', not recovered
0.325" meplat - stable beyond 9', recovered before 10'
0.375" meplat - stable beyond 7', recovered before 8'
0.448" meplat - stable beyond 6', recovered before 7'

These were all fired in a 1:14 twist .458Lott, approximately 480 grain projectiles, loaded to approximately 2200fps, from 30' above the surface of the water.

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Originally posted by Macifej:
ah-ah-ah-ah-ah-alllllffff ...!!

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Originally posted by ALF:
Anyone bothered to look at Young's nose profile factor and the penetration of penetrators into materials.

Interesting stuff.

What is better a FN profile or a round nose profile (Very important though the penetrators have to remain stable ie 0 deg yaw)

What's better, FN or RN?

In concrete, if the concrete is not thick then FN is better because it causes Scabbing, that helps penetration.

If the concrete is thick then the round nose hemispehere is the best.

What about soil? Rn is better than FN
?


In each of our target types (by mcahnical properties as I have cited before) Young's nose shape factor has been tested and proven.


The important point though is stability and this is where wound ballistics becomes complicated.

All oblong projectiles no matter what their nose shape are unstable and have to be stabilized. In practice there is not a bullet that has a true zero degree yaw

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

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What is interesting is that once the translational velocity drops to below 200 fps the bullets sides also become wetted now drag goes up and this can be seen in Gelatine, the cavitation grows right at the end of the tract, The cavity size being a function of drag.

In muscle at the end of the tract, because it's elastic the hole closes completely behind the bullet and one often will find the bullet in muscle without a visible tract, one can see it under the microscope though.

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Originally posted by 465H&H:
Ok guys you have gone too far with ALF. He presents a scientists point of view and in my opinion his is as good as your if not better, I can't believe that you would resort to ridicule as you have done rather than argue facts.
465H&H

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Originally posted by ALF:
RIP:

Thank you for that and with that said I think it's time to take my leave from AR. I can take it on the chin as much as the next man but really at my age and time in life to be subjected to this, nah not worth the effort.

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Originally posted by 465H&H:
Ok guys you have gone too far with ALF. He presents a scientists point of view and in my opinion his is as good as your if not better, I can't believe that you would resort to ridicule as you have done rather than argue facts.

465H&H

Jim
"Life's hard; it's harder if you're stupid"
John Wayne

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Factors to keep in mind--NOSE PROFILE--% meplat of Caliber--Twist Rates--Velocity--SD--Construction or materials bullet is made of--

How's that, I miss anything guys?