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quote:

1. Does rate of twist ( twist angle / angular velocity of spin) have any effect on the percieved stability of a large meplat FN bullet or a cilinder ? is it necessary to spin the bullet at all or can a FN bullet be fired from a smoothbore gun and still be stable?

2. What about the "partial" cup and core bullet ie Rhino, Northfork, Hornady MSX and now defunct Speer Bearclaw bullet where the bullet base is a solid copper shank and the and the forward cavity filled with dense lead; the effect of this based on the size and density of the lead filled cavity possibly leading to the CG of the bullet lying in front of the centre of form of the bullet?

Do we need to spin these to make them stable or can they too be fired from a smoothbore gun ?

An interesting question...
It could be argued the more stable flat nose non deforming solid design needs less spin to keep stable terminaly. Let's get one of Shootaways famous shot out barrels to try this theory on.
Will a smoothbore barrel and a flat nose bullet shoot terminaly straighter than a round nose bullet with a twist at an angled impact?

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..I know I,m thick in the head , but I would say we do need to spin stabilize them ..............But I wonder if they would need spin if the bullet was the same length as it,s diameter ??? .... Sorry no exacts there but I can see no reason the flat nose bullet could get away with something the rn and spitzers can,t

My first 50 B&Ms .500 caliber were all 1:18 twists. They were great for accuracy, and stable in flight. Terminal tests with expanding bullets were good, all stable during penetration.

Our first runs at trying to get a proper .500 caliber solid were all round nose designs, nearly a copy of the woodleigh fmj. Stable for accuracy, but when terminal tests were done they were very unstable, straight penetration only about 50%, and could not keep them in the box. We quickly put together a 1:12 twist and stability went to between 80-90% of total penetration, a marked improvement. So 1:12 did wonders for the round nose. I wanted better, so we took what was a 512 gr bullet, gave it a 30 caliber meplat bring the weight down to 485 grs (less Sectional Density mind you) and this bullet penetrated dead straight for 100% of the total penetration which INCREASED by roughly 35% over the round nose design. This in a 1:12 twist.

This was such a marked improvement I tried the FN in the 1:18 twist barrels that could not stabilize the RN at all, and guess what? The Flat Nose was 100% stable and penetrated the same amount of material as it did in the 1:12 twist.

So the flat 100% answer to the question is that the FN designed solids WILL be stable during terminal performance with a barrel with LESS twist--no ifs, ands, or buts about it! Now as far as smoothbore, I don't know, but I can say this, it has to be more stable than RN!

Michael

Herr Professor Alf,
Surely you did this bit of research long ago, and know the answer and you are soon to reveal it to us?

I do not think the CG is far enough forward to stabilize in-air flight with the North Fork (or similar original Trophy Bonded Bear Claw) ... until after expansion, but then the penetration goes down and the irregularity of the mushroom is another variable, terminally.

I could do an experiment:

Ream out a 12GaFH to .730" smoothbore,
size some 1400-grain Lead Darwin slugs down to uniform .730" diameter,
and drill out the cup point of the Darwin with a 1/2" drill,
until the slugs were well and truly CG forward,
when fired FN forward, hollow base aft.

That might be as stable as badminton birdie in air.

Then the same lead birdies could be fired through a .729" rifled bore of 1:35" or 1:36" twist, and 1:20" or 1:22" twist,
and see what happens on ordnance gelatin?

For best stability in smoothbores the CG must
be only a 1/3 or less the way from the front
of the bullet, like the Federal 10ga slugs
with a deep hollow base. Or like the
aluminum ones Rob made with HB and a
heavy nose insert. A bullet with solid brass
back and sides with a lead nose insert wouldn't
have the CG far enough forward to be stable
in flight without some spin.ED

Based on my Aluminum carrier, Tungsten Carbide Dart Stabilized bullet experiments,I believe that in a smoothbore that bullets with their CG about 1/3 (or less)of the way foreward will be stable and spin will not be necessary at all. Badmitton birdie effect! If the CG is only slightly foreward, I doubt it will have any real effect and will need spin stabilization.I suspect the FN would be more stable than a RN design once the bullet enters a more dense medium than air. Since the Northforks, Bearclaws etc are not designed this way,I believe spin will be necessary to stabilize them. As for FN vs RN vs spitzer effect on Twist, I'm Sure ALF knows the answer and is just waiting to pounce on us. The question really is does it matter?-Rob

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Art Alphin of A Square also reported deeper straight line penetration of solids with a faster twist.

A little too fast a twist is better than a little too slow.

Even roundballs shoot better "with a twist".

The longer the bullet, the faster twist you need.

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A three shot group from my 1 1/2" smooth bore cannon at 200yds.


Here can see the cars and gun.


The proj. is 1.5" in dia, x 2.65" long with a 1.125" meplat. Weight is 1lb 12oz.

I would sau they fly pretty good with no spin.

Keith

ALF

Do a test.

Get a 458Win Mag smoothbore barrel and do some shooting.

Why do rifled shotgun bbls shoot better with slugs than smoothbores?

Also think of a spinning top.
The faster it spins [short of destruction] the more stable it is.

If it is bumped it tries, and if not bumped too hard does restabilize itself.

I am not a Golfer, but I have read and do know about the "dimples" on a golf ball. However I do not think dimples would be good for a spinning bullet.

Here is why.

Bullets that have been moly coated show less of a rifling engraving on their surface, ie they are smoother.

Palma and 1000 yard shooters, including myself have noticed that there is less of a vertical change, due to windage when shooting moly bullets.

The theory is, the smoother surface of a moly bullet does not "climb" as much up or down in the wind.

quote:

No the fact is that "Normal" twist angles within the limits of what we normally see in rifles with commonly used bullets at usual hunting distances do little to influence impact conditions as far as penetration goes and thus in target behaviour of solid bullets.

OK, what does? And how do you define "Normal twist angles"? Are we headed down that "cavitation channel" again?

Alf,
O.K., surely it could be done, but would be of such limited use that it is not practical.
I will not be dimpling my bullets, nor attaching shuttlecock tails either.
I'll just keep spinning the bullets,
with more than "enough" twist.

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If a bullet could be perfectly straight as it comes from the
barrel with no barrel induced yaw, then it would fly straight.
But with regular length projectiles that doesn't happen.
So we spin those with CG near the center and use the heavy
nose/tail drag effect on those with CG 1/3 the way from the front.
Both methods stabilize the projectiles and eliminate the yaw.

Now the long skinny heavy darts used with the saboted tank
rounds from a smooth tank barrel, due to their extreme length
to diameter ratio and the long tight sabot, leaves the tank
barrels perfectly straight and can hit a car at 4 miles away.Ed

quote:

SF

OK I get SD (sectional density)
SF (Spin Factor?) Sorry, I don't know the nomenclature.

Beside, ya'll know that ALF is jerking your chain here, don't ya? Ckeck the link below.

Dimpled Bullet

I would think that it has to spin to make it stable. I always drill a hole in the flat nose bullets. Never tried a accurate shot with a FN bullet.

ALF- Do the experiment! Take your 404 put a smoothbore barrel on it and shoot some nice FN bullets out of it( you know, the common ones with their CG midway or just behind the middle of the length of the bullet. Velocity std 404 range too) Then report the distance at which it KEYHOLES(i.e turns sideways into the target) and the group of 5 shots size. My guess is that distance will be under 25 yrds and the groups will be quite large. Do the same for a spitzer shaped nose and a RN bullet. Then repeat the experiment with bullets whose CG is at 1/3 of the overall length. Bet you'll see a dramatic difference and it may be independent of nose shape. Without seeing these results I've got to question this shoulder stabilization concept. You know, I like to see the data!!-Rob

Another question. Forget for a minute what barrel twist does to affect spin rate affect on stability. Since a dimpled bullet (roughened surface) affects bullet curve and velocity, what affect do the groves on the bullet (also roughened surface) have on air flow around the bullet. Since different twist rates put different shaped groves on bullets, how do they differ in air flow around the bullet?

465H&H

Alf,
Are you not neglecting the transition from air to dense media, with angle of attack variables, etc?
I think you need spin to aid the start of penetration.

Because Gerard Shultz said so!

Regarding the other factors of bullet stability that are exacerbated by too fast spin: Are those not minor in comparison to gyro-stability at short range? What are they caused by, spatial and mass nonuniformity, concentricity nutational wobble heebeejeebies???

The best bullet for your smoothbore elephant gun would be a cylinder with hollow base and hard-alloy Flat Nose.
I suppose feeding issues will be overcome by an equally radical new gun design.

Lever action with tubular magazine???

Caseless ammo with recoilless bazooka repeater???

Rusty: SF is "Stability Factor" as in gyroscopic or spin stabilized. I never could get a working version of that SF-calculating program to download.

However, I am happy to let Alf have his way with us if he keeps bringing out such interesting finds as dimpled, curve-ball bullets.
I am at the blocked work-puter and anything gun and ammo related (and most pictures) gets blocked ... funny how they let ar.com get through ... little do they know ... will have to take a gander at the dimpled bullet when I get to my regular connection.

quote:

Are you not neglecting the transition from air to dense media, with angle of attack variables, etc?
I think you need spin to aid the start of penetration.

I was thinking the same thing but thought 99.9% of the force needed to do that will come from forward momentum. the bullet should self true in the media.

Some smooth bore and rifled 12gfh testing is needed on your waterbuffalo RIP Use aluminum darwins for the least amount of penetration and damage to the waterbuff rig.

boom stick,
Live game or ordnance gelatin is the only permissible test medium.
The Iron WaterBoard Buffalo is just a bunch of hooey.

We better get the paper punching smoothbore test for accuracy out of the way first, as Rob suggests.

But wait ... Foster-style shotgun slugs have been producing 3 to 4 MOA groups from smoothbores for ages ... soft lead, roundnosed shuttlecocks.

A brass or mild steel FN-Hollow-Base cylinder (piston) is needed for a smoothbore 25-yard elephant gun.

No worries about rifling wear.
Will a gas seal insert between powder and bullet be neccessary?

Air turbulence effects caused by the rifling engraving on a spinning bullet in flight? ...
It is not a cause of curveballs?

Does a golfball need to have spin for the dimples to produce the hook in flight?

quote:

boom stick,
Live game or ordnance gelatin is the only permissible test medium.
The Iron WaterBoard Buffalo is just a bunch of hooey.

Rip!

Glad to see that you finally see the light!

465H&H

Alf,
I can see the photo now. Did you photoshop this?

Something does not look right with the perspective on the dimples.

If "this is real" then where can we read about it?

Dimples would reduce barrel friction and allow larger loads of faster powder, and higher velocity from the muzzle, much like GSC drive bands, but better BC!

O.K. I'll dimple my bullets and dial in the hook for long range.

quote:

Originally posted by RIP:
Alf,
I can see the photo now. Did you photoshop this?

Something does not look right with the perspective on the dimples.

P.T. Barnum.

So if the image is just a mockup, the real image is still "Super Cosmic Squirrel Top Secret?"

http://www.gunsnet.net/forums/...tthread.php?t=355551

Ah ha!
The increased muzzle velocity was confirmed by the above.
BC increased by .040 also.
Also it fragments in target better than a standard jacket, if "soft" performance is desired.

Didn't find anything about the curve balls yet.

April 1.

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ALf, sorry I had seen that dimpled hoax before.

Normally, I love your techno-babble. No offense intended!

I got suckered.
Blocking on one 'puter and intermittent connectivity issues on another ... I finally got to read Rusty's link.

So this thread was just a setup to try that hoax again?

I was gonna make a few dimpled bullets in 404 Jeff and send them to ALF for testing in his smoothbore. -Rob

I don't know the answeer to ALF's question. I now am more confused than when I knew nothing.

While researching "Forsythe Rifling" for round ball black powder rifles, the notion that just enough spin to stabilize a technically perfectly stable round ball is needed due to the minute imperfections in most balls. Too much twist magnafies those imperfections and leads to inaccuracy.


Perhaps relying soley upon bullet profile for in-flight stability is insufficient to counteract bullet imperfections and a minor amount of spin is necessary to correct this?

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Alf,
F__ing with the idiots again I see!!!! You must be very very bored!!