I'm concerned that thin walled brass or aluminum would collapse the case like an accordian before the bullet even started moving resulting in extreme high pressures.
As far as research goes, I have the feeling that all of this may be known. The trouble is where to find the information.-Rob

A 375 bullet would take away the shoulder to have a simple tapered case and be stronger.

Isnt it worth a try?

That brass is only .013-0.010 thick. I'm not comfortable with that little thickness.-Rob

quote:

As far as research goes, I have the feeling that all of this may be known. The trouble is where to find the information.

This is always a problem. Large institutions have people who 24/7 look through the literature for such prior work.

I'm surprised no one has already given us chapter and verse on prior art. Meanwhile, I'm comfortable to keep going as long as results look promising. If it already exists, why ain't somebody SELLING it?

Here is a hydraulic high-pressure chamber which could be used to “crunch†test samples such as thin-walled tube sections. The single piston has 700 psi air on the large-area side, and a cavity filled with hydraulic oil on the small-area side. Because the ratio of the diameters of these two piston sides is about 12 to 1, the area ratio is about 144 to one.

A section of thin-walled tube, sealed at both ends, could be dropped into the test chamber and covered with oil. Then the piston would be dropped in through the O-ring seals, and up to 700 psi air pressure applied to the piston top. Then pressure is dropped and the test part recovered and measured for any dimensional changes.

If anyone is interested in actually building such a “cruncherâ€, here is an improved design:

“http://img.villagephotos.com/p/2005-4/986073/hydraulic2000psi.jpgâ€

Rob, you are right that too thin an aluminum wall will lead to some sort of axial failure in that wall, like the “accordion†failure you mentioned. But note in the exaggerated sketch above the carrier back-end get squeezed into the rifling of the bore, effectively reducing the pressure which the outside of the carrier “seesâ€. So the predominant force on the thin carrier walls will be along the axis of the bore, the force attempting to accelerate the heavy bullet at the front of the carrier.

But hollow carriers can be so much lighter than solid aluminum carriers that I think they would contribute notably to dart stability.

This is probably a minor issue at this point, compared to the flight-dynamics issues...

quote:

Originally posted by Henry22LR:

quote:

As far as research goes, I have the feeling that all of this may be known. The trouble is where to find the information.

This is always a problem. Large institutions have people who 24/7 look through the literature for such prior work.

I'm surprised no one has already given us chapter and verse on prior art. Meanwhile, I'm comfortable to keep going as long as results look promising. If it already exists, why ain't somebody SELLING it?

I don't know of any work directly on this subject, but would the dynamics be simialer to throwing Javelin? They are designed with the CG ahead to the center of pressure. This is done to assure the javelin lands point first. Do the fins on a throwing dart balance out the lift so they do not go tip down when thrown?

A throwing dart or even a javelin has no “lift†because all the surfaces are symmetrical, so no surface can develop differential flows over them. So neither can counter gravity, and pretty much travel in an arc, ballistically. So does a bullet.

The point in dart-stabilization of a bullet is to keep the projectile traveling point-first, like a javelin. As you said, the center of gravity (center of rotation) must be forward of the center of force. And there are two centers of force, one aft of the CG and one ahead of the CG. We also want the aft center of force to exceed the fore center of force by a goodly margin.

This is pretty easy to accomplish in a long javelin, but more difficult in a fairly short stubby bullet. Apparently Rob’s bullets are doing it, as he reports that these things always hit point-first when dropped from any height.

Something which has always bugged me about spin stabilization of bullets is the extra ENERGY which must be extracted from the burning powder to impart the high spin to the bullet. All this extra energy could be used to impart higher velocity (and energy) to the bullet, rather than to imparting SPIN.

I know that the spin is for gyroscopic guidance of the bullet, and it surely must work pretty well, judging by the industry which has grown up around it.

Blowguns use dart stabilization, and work pretty well. But a blowgun dart drags along a “tuft†behind it, in order to increase the aft area, and these tufts are pretty lossy, creating quite a drag. This drag slows the blowgun dart in flight, which limits range. The fins on an arrow perform similarly.

So I look forward to Rob’s field tests of smoothbore firings of dart-stabilized bullets. Or even firings with slow-twist barrels. Will we find that spin-stabilization can become an historical artifact, relegated to museums? THAT would be a hoot….

I'd really like to start on a 12GaFH version of this dart carrier with a interference fit tungsten carbide 5/8 rod blank in the nose. It could be easily made with spring loaded fold out fins for additional stabilization. I hate the wait to for the .45 barrel to arrive.
I also tested some .620 cup point borerider bullets out yesterdasy made from copper and brass. They worked extremely well. All rifling engraving was on the rear of the bullet and none on the front. This was with a three groove 1:20 twist .600OK barrel. Accuracy was excellent and I also noticed a marked rerduction in felt recoil so much so that I let a friend who had never shot a .600OK before try it and he had no problems at all. Even wanted to shoot it some more. we went through 25 rounds which is alot from such a powerfull gun. Unfortunately its a tough balancing act between bullet length ( for case capacity) nose shape ( for reliable feeding) and weight. I finally found a combination that is very close to ideal and still weighs 900 grs. I'll post some pics later.

That’s very exciting, Rob. Although I doubt the bullets you describe had dart stability much over 1.1 or so, maybe the very high dart stabilities of around 4.0 aren’t really required. One thing you could do is balance each projectile on a razor edge, in order to estimate its CG. The higher dart stabilities will have CG’s moved towards the front of the bullet. They will generally be composed of a very heavy front weight and very light rear weight. The total surface area of the bullet both fore and aft of the balancing point is important too. In fact the aft area, divided by the fore area, is what I’ve been calling dart stability index.

The tungsten carbide heavy tip will be exciting too, I expect. And the low recoil is very interesting, and is yet to be explained.

How would .50 cal BMG bullets do? I had an Encore barrel in the .50 American Eagle, using the 50AE case opened to fit .510" diameter bullets. I had some uncut full length 50AE brass with the .308/30-06 rim diameter. No experience on these machined bullets here, but there is a lot of .510" heavy bullets out there, and surplus ones for cheap shooting. Sorry to get off the 45 ACP case, but just a thought?

quote:

Sorry to get off the 45 ACP case

No problem, HH1812. Some of these heavier dart-stabilized projectiles probably need to be in cases larger than 0.45. Let's run with it.

“I'd really like to start on a 12GaFH version of this dart carrier…
This was with a three groove 1:20 twist .600OK barrel…â€

Rob, I’ll run any dart-stability “simulations†you want, if they might be useful to you. Also on the 50BMG cases, when you are ready. About all I need for a half-assed simulation is projectile OD, front material, back material, whether wasp-waist or not, and projectile OAL. Oh, and “pointy†or blunt nosed. These won’t be perfect simulations, but might help point you in some particular directions and save you some time.

Why do you think the perceived recoil was reduced?

I am going to have to start with an H&R "Ultra Slug" so I can have some low pressure 3" brass to shoot darts, whenever they are on the market.
A game of 12 Guage darts would be fun, with the dart board at 100 yards on an earthen berm.

Yeah, those supersonic 1000gr tungsten carbide tip darts ought to stick pretty well in a ¾ inch plywood dart board, lol…

Oh, wait…

Maybe you better put the dart-board BEHIND the elephant…

Rob, as you know, to get higher dart stability we like to use very light carriers with very heavy tips. The trouble with aluminum carriers is that they are SO VERY light, and don’t add much mass to the bullets: most of the bullet mass comes from the heavy tip, and very little from the carrier.

But you are talking about tungsten carbide points, which are pretty dense at 15.6 g/cc. Maybe we could make carriers from zinc (7.14 g/cc), which is pretty light compared to tungsten carbide. I know pure zinc may not be too strong, but there is an alloy Prestal®, an alloy containing 78% zinc and 22% aluminum, which “is a strange material that is nearly as strong as steel but is molded as easily as plasticâ€. Also called Zinc-aluminum or ZA. It is available in bar stock.

Based on its composition, I would expect its density to be about. 6.16 g/cc, which makes tungsten carbide over 2.5 times as heavy. Maybe this would be a light enough carrier to give good dart stability, yet heavy enough to add some weight to the projectiles.

I'll run some cases tonight to see what the "best" bullet weight is...

Henry and RIP-Here is a 12GaFH borerider carrier with a .50 BMG AMax as payload. I just scaled up the .45 version and made it a little sexier. Originally designed for a .50 tungsten carbide penetrator just to see how it works. In a 12GaFH shell this thing really looks Black-op ready. Man is this thing weight foreward too.-Rob

quote:

Originally posted by Robgunbuilder:
Henry and RIP-Here is a 12GaFH borerider carrier with a .50 BMG AMax as payload. I just scaled up the .45 version and made it a little sexier. Originally designed for a .50 tungsten carbide penetrator just to see how it works. In a 12GaFH shell this thing really looks Black-op ready. Man is this thing weight foreward too.-Rob

Darts anyone?
Let's play!

Great work, Rob!
And thanks to Henry for goading this along.

Do you think the dart will lob down range from an H&R "Ultra Slug" with 3" brass?
Twist of 1:35" will be O.K. with that dart stability, eh?

RIP- Beats me! I honestly dont know if fast or slow twist is needed with these things. My .600oK boreriders are only 1.6 inches long and stabilized from a 1:20 twist barrel. It willl be really interesting to see what spin and dart stabilization do together. Basically I see no issue at all with 3 inch brass cases.
As far as the carriers go I need to price out .750 6061 aluminum alloy bar stock ( cant be very expensive compared to copper). PGM is written and proofed( although I'll need to optimize the speeds and feeds), so all I have to do is figure out the cost.-Rob

Have H&R ULTRA SLUG.

Working on shotshell reloading gear and components, new thing for me, sorely neglected in misspent youth, even though firing a 12-guage shotgun at 8 years-of-age (and having my Pop catch me and the gun as we went flying), is how I got this way. Thanks Pop!

Fun, fun, fun ... like a kid in the candy shop.

I have a TC Encore bored to 12GaFH with the barrel cut back to 16 inches and a screw on 10 inch piece of ER shaw 12 Bore barrel on it. Made a forcing cone in the rifled stubb ala paradox gun. Might work pretty well with this concept. Back at work right now so cant do any testing for two weeks.-Rob

Rob,
Thanks for the ideas. I will be learning to cast Rippalloy "Ultra Slugs" for my po'man's 12GFhelluvit. Someday I may graduate to full 12GFH (3.850" big toy). Whatever and whenever you get around to stocking inventory let us know.

Well, its definitely a compromise. The dart stability dropped quite a bit but the grains went up to 800. I guess only shooting will sort this one out...

Have fun at your day job, Rob. See you in a couple of weeks.

Henry

quote:

Originally posted by Robgunbuilder:
12GaFH borerider carrier with a .50 BMG-Rob
http://www.hunt101.com/data/500/medium/IMG_01741.jpg

Thats pretty close to just loading a entire BMG cartridge as a projectile.

Yeah Kristofer, just add some kind of an impact fuse, make it a fragmentation case, use faster powder and you have a mini-mortar which can be launched by a rifleman.

This picture is from Marty of Teppo Jutsu, who posted it awhile back on AR15.com.

It is of three custom turned .458 SOCOM projectiles. On of which is a 86gr Gapping Hole Hollow Point, turned from Al, of the same dimensions as the GHHP of pure Cu at 275gr.

The Al GHHP got very high velocities and good accuracy at 100(y/m) when he tested them. And again he reported not fouling issues with the Al projectiles. Which I still find amazing, considering how Al glues its self to cutting tools.

That’s two thumbs-ups on aluminum from two well-respected authorities. Looks like aluminum is OK…

Well I agree that aluminum seems to work and thanks for the info. Perhaps marty will jump in here and tell us about his experiments.. I too was amazed for the same reasons you mentioned. I also like the idea of a internally scored HP but with a Tungsten Carbide "anvil" in the front for a FN penetrator that will open up deeper than std bullets. the problem with very light bullets is they are "bombs" on impact and dont penetrate well. We can design great penetrating bullets and great bullets that open quickly, but what we really need is a great penetrator that also opens enough to create a large permanent wound cavity. Thats where so far copper is the best compromise. Finally, Its also clear that the larger the bore size, the heavier the bullet and the faster you drive the bullet the better the penetration.-Rob

A bit more on the .458 caliber 86 grain aluminum pills. They are made by Lehigh. Reportedly they are surpassing 3000fps from a 10.5" barreled 458SOCOM. Exciting!


Follow this link to the thread on these bullets @ AR15.com.

Henry, I'm thinking rotating the motor so when the recoil comes back instead of twisting, it pushes itself down.

Tyler, I'm thinking the gyroscope (motor) would resist the attempt to push it downwards, but would also induce a twist in the rifle. I'm not sure how this twist would feel.

I guess I need to get a toy gyroscope out and play with it some...

Found this interesting discussion from 2004 here:

Machinist discussion

No, these are not 45ACP bullets, but are 50BMG bullets. And some are “boreridersâ€, in that the bullet only engages the barrel rifling at the extreme aft end of the projectile. And the lower bullet in the photo is called a “very low drag†version.

The heaviest of the bullets shown is 850 grains.

All this leads me to believe that the 50BMG bullet market is really READY for a highly dart-stabilized version.

The best carriers can probably be made of alloy RZ-5, an aircraft alloy of magnesium and aluminum, which is about 2/3 the density of aluminum. Very light helicopter transmission casings are now usually made of RZ-5, as are the best transmissions in Formula I racing.

Of course, because of the combustibility of magnesium, exhaustive tests will need to be conducted. Also, a layer of lacquer on the stern of each bullet would probably be indicated to limit ignitions.

RZ-5 magnesium/aluminum alloy

In the figyre above, I should have said the optimum meplat diameter is 15% of the projectile diameter, not 0.15%.