Tht sounds perfect Rob. Leave just enough
at bottom of first hole to seal the bottom
and no threading needed. What total weight
are you planning on.Ed

Ed- Yup thats the plan.I'm going try aim for 1000gr. What do you think?-Rob

I think this is what I'm reading about, so I'll run the cases tonight.

Sounds good. Henry I think the 3/8 hole
Rob planned for the 12ga size. If it is .625
carrier a smaller hole. May ownly need a
1/4 inch of material at bottom of hole.
And it could still have some wasp waist
effect for a 1.5" in the middle section.
That would cut friction a little.ED

How about a boat tail and a champher on the top?
The boat tail might mess with the dart stable thing but be better on down range speed. Also the boat tail and champher would reduce friction and preasure. What say the scientists?

I don't think this thing is going to do much in the realm of long range, but at <100 yards it should be a behemoth!

Even at 50 or 100 yards the boat tail would have an affect.

Yeah, I got crossed up. This is for the 12GaFH version...

These things really are PEVERSE! About like trying to stack fresh watermelon seeds. But FINALLY I think I have figured out one thing:

PEAK DART STABILITY OCCURS WHERE CG=TRANSITION.

Why this should be so, I don't know. But what it means is size the carrier to just the right length so that the projectile balances at exactly the back end of the heavy tip, and that will give you peak dart stability.

I doubt this will work for wasp-waist designs.

I guess the good thing to come out of this is that you can see the drilled-out (lightened) aluminum carriers give a higher peak dart stability. I’ll be the first to admit that we really don’t yet know how high a peak dart stability we really need for practical dart stabilization. And we won’t know until many test rounds have been fired.

But tonight I should be able to change the computer program around so that I can tell it the desired projectile grains, and it will tell me the proper dimensions to get peak dart stability with that overall projectile weight.

Boomstick-Actually boat tails are no advantage at all over FB bullets out to 300yrds or so. Just ask the 6PPC crowd. Past 300yrds they do have a positive effect. The only advantage on a 75yrd gun like a 12GaFH is a boattail makes it easier to load the bullet into a case.
Henry22lR That looks good except the Bore is .729 not .719 for a smoothbore and .729 driven section and .719 land riding section for a Borerider.
So from this chart I need to make a 1.875 inch long Tungsten carbide insert. Now thats gonna be expensive! Migth as well just use a Tungsten carbide 5/8 screw machine drill in the nose. -Rob

It looks like that the 1036gr
or thereabouts that CG will be about
1.07 inches from the front with 1.680
inches behind. That may be perfect.
That is the same proportions on a Brenekke
KO slug which is only 1.5" long.Ed

Rob:

The peak dart stability happens at 1665 grains projectile mass, rather than the 1000 grains you wanted.

But the length of the tungsten carbide insert is only 2.75-1.875=0.875 inches, not the 1.875 you mentioned. [Overall projectile length minus transition length.]

I’ll run the cases again tonight, and I expect to get your 1000 grain projectile in an overall projectile length of about 1.65 inches, 0.52 inch tungsten carbide length, with a dart stability of about 4.5.

Henry- excellent! I'd like to keep the carbide under 1 inch for cost reasons. Also see what can be done with .500 diameter carbide. The 5/8 stuff is too expensive. -Rob

Rob:

I believe the “5/8 tungsten carbide†you mentioned was reduced by you to 0.618. I assumed this is because it is labeled 5/8 but actually measures 0.618. On further thought, I realized that it may be delivered out-of-round, and you can only net 0.618 true diameter.

What actual OD do you expect from that tungsten carbide sold as ½ inch? Or is the 0.500 you mention a reliable diameter?

Rob, also, can I “cheat†by making the drilling in the aluminum slightly larger than 3/8?

Henry22Lr -OK try a 7/16 hole in the carrier. I'd still like to use .500 carbide. I will ream the carbide insert section to .498 for a interference fit. The .618 is the aluminum diameter I was going to ream to in order to get a .002 interference fit with .620 TC rod.-Rob

These are about the best possible for 12GaFH right now. Note they all are clustered around 1,000 grains with dart stabilities around 6.0. The overall projectile lengths are only 1.85 inches, yet with the high cross-sectional density I hope we’ll see great accuracy and great velocity even at extended ranges.

I used the 7/16 drill. These carriers are so short and stubby that I really don’t think there will be a problem.

Still using the 5/8 tungsten carbide, but we don’t need to fire too many in order to see if we are “on to†something here. The fact that the curve is pretty "flat" encourages me that these will be pretty tolerant of minor differences in the dimensions I used and those required to make practical bullets. I hope these will be "the ones to beat" for quite a while.

Good shooting, you guys!

1000 grain 12GaFH

Using a 3/4 inch long lead insert and a slightly longer aluminum carrier, a peak dart stability of about 4.5 can be attained. This is not as good as the dart stability of 6.0 with the more expensive tungsten carbide, but is much lower cost in materials.

Here is another view of my 700HE blaster,
that I got rigged up on an action and stock.
Side view shows action with a aperture sight I
rigged up. Also cases. On left is 700H 3.25" case.
Center my 700HE, what the gun in picture has now.
Good for nearly 23,000 ft lbs, we attained in
a work up in testing with the barrel as a test
barrel with screw on testing receiver....Ed

Wanted both on the same page, better showing scale.

Now we are down to lengths where we can
get a good charge of powder behind them.
If Rob uses 1/2" carbide I think one the
length of your 2.35" one will do.ED

Ed, you are right about the two 1000 grain 12GaFH projectiles. But a little caution:

The ¾ in. lead insert used in the longer projectile is 645.7 grains. The 0.8 inch tungsten carbide insert used in the shorter projectile is 710 grains. But using the smaller ½ in. diameter tungsten carbide, it would take a length of 0.83 inches to weigh 645.7 grains to be used in the longer projectile.

Perhaps this is not much difference, but until I run the case I won’t be entirely comfortable. I’ll run it ASAP.

You were right, Ed. The 1/2 in. tungsten carbide 3/4 inch long in the 2.35 in. carrier is about as good a dart stability as the larger dia lead insert of the same length. Plus, it gives a larger wall thickness in the aluminum for a stronger hold of Rob's interference fit.

But materials cost are MUCH greater. But at 1000 gr, can't do much better with 1/2 in tungsten carbide.

quote:

Here is another view of my 700HE blaster,
that I got rigged up on an action and stock.
Side view shows action with a aperture sight I
rigged up. Also cases. On left is 700H 3.25" case.
Center my 700HE, what the gun in picture has now.
Good for nearly 23,000 ft lbs, we attained in
a work up in testing with the barrel as a test
barrel with screw on testing receiver....Ed

Ed, I really admire your Blaster! Obviously a serious working-class piece designed for serious load development, and not as eye candy. A welcome relief from some of the "prissy Pretties" over on Gunsmithing.

That is great Henry, as Rob said he had a
lead on 1/2" tungsten reasonable.
And the CG and stability matches the
Brenekke KO slug that guys with smoothbores
are getting 2" groups at 75 yards. Ed

Rob, these calculated results are so disconcerting to me that I thought they needed to be posted on this Thread. This will require a lot of work to sort out, so I will post any further work on them to my “Subsonic Shooters†Thread unless you specifically ask for me to post it on this Thread of yours.

Basically, it is a warning that the blunt bullets I have been designing for best dart stability also carry a major deficit in aerodynamic losses. At least when compared with the ellipsoidal bullets, which are about the least lossy profiles I have found using AeroLab.

My continuing work will include trying to find a bullet design which combines both good dart stability AND an ellipsoidal shape.

As you and Ed begin your tests, I want you to be aware that any unexpected or incongruous results might be related to aerodynamic losses, and not to dart stability.

quote:

And the CG and stability matches the
Brenekke KO slug that guys with smoothbores
are getting 2" groups at 75 yards. Ed

Ed, that is really good to hear, that maybe some of this dart stability stuff has been stumbled onto before...

And now the question is: did Brenekke come on to it the hard way, by cut-and-try, or the way we are proceeding, by relying on computer simulations?

Henry- I actually dont see a problem. The TC can be shaped during the sintering process to any shape we want. I will be knocking out a few 12Ga prototypes this week. Remember these things dont get shot at 100meters usually. 25 meters is more what we expect.-Rob

Brenekke has been doing this for many years,
probably trial and error.They and others have
used all kinds of locked on light wads
onto the back of hollowbase lead slugs.
Try to find a Brenekke KO slug and balance
it. Only 3 bucks a box and cut the slug out
like I did for testing. It balances(CG) at
the middle of the slug with a locked on plastic
base .850" long. Total length is 1.48"

Rob I hope you do the 2.35" version with
your .5" inserts. leaves more powder room.
As for ballistic coeffecient a slight taper
to the top of aluminum and with insert out
about a .100" with same taper on its corner
to a less than insert diameter, and
shazzamm, you have a big game flat point.
And a fairly good ballistic coefficient.
And you have the equivalent to big flat nosed
big game slugs, turned or swaged. ED.

Thanks, guys, for both your comments. It is indeed a pleasure to be working with such reasonable, practical people.

I guess the most practical additional suggestion I can make is:

Don’t feel bad about rounding corners on the front of the bullets, without losing too much of the heavy inserts. Just about any “softening†of the hard, flat front end of the bullet will do LOADS towards decreasing the drag coefficient Cd.

Rob, I'm going to run some cases on these. I don't know what max grains they will be with good dart stability, but I intend to find out.

Also, I have 2 questions:

1) Is 308 caliber or 338 caliber (or some other) the best round for absolutely the best long-range round, based on the benchrest contests? I guess I mean 1,000 yard shooting.

2) What grains should the bullets of 1) be?

I'll be developing these in my "Subsonic Shooters" thread...

Off topic, but back to your recoil reducing device Henry, what if you turned the little motor so it was spinning "towards the muzzle"? When the recoil came back it would want to shoot down, maybe counteracting some of the muzzle rise as well. It would act like a muzzle brake without the extra noise, or shoot something with a brake and the device and have a whole lot of noise without much recoil.

Currently for match shooting it's probably 6mm or 6.5mm, but for absolute best BC and past 1000 yards, probably 338, 408, or 50 caliber. 338 is a good compromise of recoil and real good BC.

Tyler, let's take this discussion to my "Subsonic Shooters" thread if you don't mind...

1) On the 338 cal, looks like 250 or 300 grain projectiles are "best", right?

2) I don't understand your question on the rotation of the motor. Are you suggesting rotating the motor's axis to be 90 deg from the barrel's axis?

How about putting a canalure on the bottom 1/2" so most of the dart (The bore rider part) will be outside the shotgun case for brass shells as to leave more room for powder and lower preasure ect. The thing will be about 6" long but man would that thing fly! Obviously this would be for break open actions.

I got some 3/4 inch aluminum rod yesterday so will make some bullets today for testing. I've been doing some studying on TC processing and making any shape is easy to do its the kiln neededed for the sintering process that I have to deal with. It takes some serious heat to produce a copper matrix to hold the TC particles together. A flat nose design should be realatively easy to make as I have some TC rod and I have a few to try out today.-Rob

Rob, isn't copper used as the matrix for holding tungsten powder together also?

Henry- Yup, Copper or nickel are commonly used for the matrix that holds Tungsten carbide particles together. The process is called sintering. Requires high temps but a mix of wax, copper powder and Tungsten carbide powder is actually very moldable and easy to work with. The sintering process basically requires melting the copper or nickel binder.
I made some aluminum 12 Ga carriers yesterday. I need to make some pgm adustments today to optimize dimensions and add the TC insert. I'll post pics later today.-Rob

Anxiously awaiting the pictures, Rob.

When you get a fairly close estimate of the final density of the TC/Cu inserts, I’ll run some “cases†as to dart stability.