Finned 12ga slugs

The sketch shows what is essentially a cylinder and that's going to have the stability of a brick.

The fins as shown are not going to impart any stability to the projectile. Fins act, if I can remember my theory, by imparting a turning moment on the projectile. They can do this because they are at the back of the projectile. If you put fins the the front, they would do it, but would be unstable and the projectile will tend to assume a more stable position, with the fins in back. If the fins were in the exact, precise centre, they would do effectively nothing unless canted. The force exerted by your fins is essentially in the centre of the projectile; any force imparted by the fins on the back half will be cancelled out by the fins on the front half.

Even if you canted the fins, you're not going to get gyroscopic stability, that stability imparted by rifling or by a turning bicycle wheel. All that canted fins can do is cancel out minor imperfections in a projectile that's otherwise stable.

The Foster slugs are essentially stable because the centre of gravity is well forward; the hollow skirt, I guess, provides some flare stabilization. (Flare stabilization is not as common as fin or gyroscopic, but has been used from time to time. Picture an arrow without fins but with a small cone on the back. Unrifled air guns can still get modestly good groups because of the skirt on the typical waisted pellet.) Your slug design appears to have the centre of gravity more or less dead centre and it's going to start tumbling the instant it leaves the muzzle. Actually, the longer you make the nose, the further to the rear the CofG is going to move and the less stable it will be.

It would be pretty good from a rifled shotgun barrel, I would say, but from a smoothbore, you'd better be in bayonet range to get a hit.

I think the fins were a better idea.

Sorry.
 
This is making me wish I had taken some courses in aerodynamics....but what you're saying makes perfect sense. Which brings us back to the first design, with mass forward and fins on the back. Stupid laws of physics causing problems. :p

I guess I could do something of a hybrid between the two. Smaller diameter cylinder or diamond at the front and extended fins. I drew up my initial design but with a 1.175" overall length and I think I can get away with this easy enough lengthwise and the design ends the diamond's tail somewhere about 3/4 of the way down the length. Actually it looks like the profile I first posted before I did up drawings based on calculations.

Getting deeper into this and doing some basic visualization of air flow over a projectile the flared base design makes a lot of sense for drag stabilization. Even the foster slug works on more or less the same principle. The fins are proving to be a problem for the drag stabilization without going to excessive length it seems. I can see my initial design flying more or less straight and should it try to tumble the fins would force it back into a 'straight' flight, however if too short they may allow excessive pitching and yawing during said flight. One would(I think) have to extend the fins back to the point where laminar flow begins to converge again to prevent excessive pitch and yaw, which is where the flared base design makes more sense because it's close enough to the more laminar flows that it either directly engages them the whole time or there is minimal movement before it does. With the fins it seems one would have to pitch to the point where the fins perpendicular to pitch direction engage the laminar flows rather than the turbulent ones and cause the bullet to kick back into alignment and stable flight when the fins engage the mostly laminar flows full time.

The Brennekes work on the same principle as the flared base it seems. By having wadding attached that is lighter than the main projectile and likely slightly larger, it would engage the more or less laminar flows and prevent excessive pitch and yaw to the projectile. From what I've read the "rifling" on these slugs is to allow them to pass through chokes easier rather than to impart any relevant spin etc. The Brenneke would probably have better ballistics just due to the fact that the mass of the bullet is entirely forward of the stabilizer, rather than being part of said stabilizer. The nature of the front of the Brennekes though one would think makes a long-ish wad a requirement to attach to the slug as it would cause some serious turbulent flows down the side of the bullet meaning a longer convergence distance of laminar flows.

Hmm...almost thinking it's just easier to make Brennekes at this point in time and scrap this finned idea given it would require some excessive slug length. I was thinking it might simplify loading by creating a slug in a 2-part mold that one could just drop in a shell and go. I wouldn't mind using the Lyman slug but I really don't like the flat nose design to it, and fosters I can buy easy enough to make re-loading not worth the effort.

*edit*

Also just came across this thread where a guy tried just this and had problems with a 4 finned slug with some cool designs. Almost exactly what I was describing above. Seems there is some issues with bearing surface on the 4 finned slugs from the limited post but I can see this as given fins that are not fully engaged in the laminar air flow, it would take a larger surface to exert enough force to stabilize bullet flight.(intuitively I'm thinking cylindrical area of turbulent flow directly behind the slug and stabilizing surface is a plane cutting into the laminar flow outside said cylinder. As the bullet pitches bearing surface increases, but during 'normal' flight might not have enough surface engaged to keep the bullet traveling straight.)

Link:

http://gunloads.com/castboolits/showthread.php?t=46571
 
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I'm thinking that I am going to abandon this finned slug pursuit unless someone can toss out an idea that has lots of merit. Thanks for the ideas/discussion guys.

I'm thinking that Brennekes are the way to go as they have been shown to be effective out to long range and to pack one hell of a punch. Since I'm mostly looking short range these will be more than accurate enough without all the headache of realizing the design you came up with is crap.

I'll probably just make one out of 3 pieces of flat steel for the moment unless I come across a nice block. Main body will just be an 11/16" cylinder(~0.69...likely end up 0.7-0.71) drilled through appropriate thickness of metal. Nose plate I'll just use a smaller bit to create the center point for the semi-wadcutter design and for the base a tapped hole with a screw in it to make the hole for attaching a wad(obviously filed to a point with no threads on the mold side..). Simple and it will work. Little bit slow on the casting side but more or less free.

Ideally I wouldn't mind getting a nice 3-part mold with swag grooves to give a night tight bore fit in all shotguns and prevent choke damage in non-cylinder bores. Probably be that 'lead sabot' round with shorter fins. Joy of a Brenneke is they are simple...it's just no one makes a bloody commercial mold for one. And I would imagine given a tight bore fit they would be killer in a rifled barrel.
 
Eureka!!

So I was thinking about the best Brenneke design and in that link above it was mentioned swag groves/fins so that one can fire a hard cast projectile out of many different shotguns/chokes and still have a tight bore fit. After a bunch of thought on mold design I recalled a thread I read about a guy in africa who was trying to make shotgun slugs because ammunition was scarce and there was high political instability.

The solution: a 16mm socket. Which just happens to have a diameter of 0.735-ish at it's largest point. Namely the points of the socket(hello tight bore swag fit :p ). A 5/8ths socket is 0.725" which is just under theoretical bore diameter of 0.729". So I'm going to have to pick up a few sockets to play with when I go to town next as I do not wish to destroy my socket set.

I'm thinking if one drills and taps the socket wrench hole and installs a bolt with a conical hole drilled in then end, it would make a nice point for the semi-wadcutter profile and an easy way to remove slugs should they stick(just screw it in a bit further). Then just drill an 11/16 hole in a board, drop the slug in, center the screw hole with an 11/16 bit, then swap to a smaller bit to drill the screw hole. To adjust weight just grind the socket down until it casts the correct weight.

Ahhh simplicity in using what's on hand. I just wasted several days on this finned crap and at this point I could have already had slugs being cast had I just looked in front of me. :p

Now the hard question...6 or 12 point? :D
 
I recon that Y-man, had a few problems with stability of those projectiles, he later got a Jeff Tanner roundball mold and seem to have better luck with them...
but keep up the good work, let us know what u make.
 
Thanks and I will ;)

I think Y-man's issues were that when he created the Brenneke style out of them he had limited resources and just used the wad that came with the bird shot to attach to the slug(which he did say all hit the target and 'point' first). In addition it looks like they weren't that straight. With a properly centered hole and felt wads one would think that you could get a straight flying projectile. But really a socket has the perfect shape/size to make brenneke shotgun slugs. Ya you won't have the tapered swagging ridges so it'll be harder on a barrel if you fire it through a choke...but seriously?...who fires slugs through a choked gun if your hand loading them?

As an update to the finned slug thing...I may just revoke my earlier statement about full on abandoning this pursuit. The guy at Lee sent me back a 3-d pdf of my earlier drawing and playing with it I think if I just narrow the center slug a bit and lengthen the fins I can get a decent stable projectile. The narrowing of the central mass would be fairly key as this would allow laminar flow to return more quickly to contact with the fins, in addition to a slightly lengthened projectile. Apparently my rough calculations by hand(based on perfect geometric figures) aren't all that terrible as the guy from Lee stated that calculated mass from the model was 567gr or 1.296oz(I was aiming for 1.25oz with wheel weights).

*edit*

So doing some drawings, I can make (I think) a stable slug in a couple different ways. First, and easiest, is to add a 0.075" or so base plate on the current design. This would effectively replicate a flared base like one would find on a Lyman 525gr wadcutter, but with the hollow on the outside rather than the inside. May or may not be as efficient flight wise, but I would assume similar flight characteristics with drag stabilization. Center of gravity would likely be further back than the Lyman as they use a flat nose, and this one is 0.42" on the flat part of the nose.

While this would effectively replicate a flared base design for ballistics, the advantage that this would be doable in a 2-part mold(also looks cool...looks count for like half the reason things die...right up there with expansion and bullet weight retention). Downside is that molds have to be cut on a CNC mill rather than a lathe. Not sure if Lee charges any more of the milling or not.

Anyway on to the second design. The second design is similar to the 'lead sabot' I posted earlier only designed to fly stable out of a smooth bore. Bullet mass is in front of the fins to allow some drag stabilization. Central mass is about 0.530" and the fins are 0.729", giving a full bore fit(still need to calculate weight though). I think this design would also work well but is kind of going for something a bit different in that it is more of a sabot round. That being said if one made this round and added the flared base to it, it would fly like a dream. If I left the base off of it and fired it through a rifled barred this thing would be a massive gyroscopically stabilized gopher seeking missile (what?...you didn't think I was using these on large game did you? :p ).

Anyway both of these designs offer something new-ish. I'm kind of tempted to pursue the lead sabot design as it is something that does not exist yet on the market as far as I know. This would require me to buy a new barrel(/shotgun) though...strictly for research of course. For the first design I think the main advantages are nose profile and 2-part mold.

Really with drag stabilized slugs I think Brenneke kicked my ass on this 80 years ago. Mass as far forward as possible(solid cylinder of lead), drag stabilization as far back as possible(wad extending behind the slug), maximize mass(both wad and slug hit target...wad adds extra weight/energy), and able to be fired through any shotgun with tight bore fit(swage lines at angle to facilitate swaging of the slug by the choke if it needs to).
 
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So a preliminary sketch of a 'lead sabot bomb slug'. Has the full 0.729 diameter riding on the fins, projectile is 0.52-ish, and there is a disc of lead on the very bottom that is 0.68 in diameter to impart drag stabilization. Thoughts? No need to be technical, ego boosts are cool too. ;)

sabotbombprelim.png


*edit*

Add some caps of the 3-d model. Props to Patrick at Lee.

leadbomb1.png


leadbomb2.png


leadbomb3.png
 
So I think I'm going to go with the latest design just because it has the potential to offer something other slugs do not. I feel that the initial design with an added base imitates the lyman 525gr wadcutter enough that it doesn't merit an experimental mold at this time.

Now for the new design I have made 2 drawings. One is 1oz(first drawing posted) and the second is 1.25oz. I'm a little torn as to which way I want to go with this as I've always been partial to heavier projectiles, however I feel that the 1oz could take greater advantage of this design due to lower air resistance. The 1oz design uses a central mass that is 0.53" in diameter while the 1.25oz uses one that is 0.60" in diameter. Both are smaller than a traditional shotgun slug(0.680"), and both are significantly smaller than full bore slugs(0.729"). Commercial slugs are designed to fit through a full choke which is where the 0.680" comes from.

Anyway I cropped together 2 bad images of the drawings for comparison purposes(used a camera...don't feel like installing my scanner...by that I mean I can't find the disc :p ). Both are for all intents and purposes scale to each other. Just not quite aligned. Anyone have an opinion on which they would prefer? (1oz=437.5gr and 1.25oz = 547gr)

comparison.png
 
Here is a nose profile. Man I really need to find that disc for my scanner. Or track down the drivers online...

Also I don't have a compass. And my sketch skills suck.

nosecomparison.jpg


*edit*

Did some overlay in paint to make it more bold.

nosecomparison2.jpg
 
It's not your sketching skills, I think. It's a gestalt problem at my end.

What I am seeing is essentially a tear-drop shaped body, four fins and what amounts to a solid, shallow washer or disk at the base for flare stabilization. Is that correct?
 
ATOM said:
It's not your sketching skills, I think. It's a gestalt problem at my end.

What I am seeing is essentially a tear-drop shaped body, four fins and what amounts to a solid, shallow washer or disk at the base for flare stabilization. Is that correct?
Click to expand...

That is correct. The fins have been downgraded to stabilization status in the bore only and the disc at the bottom is now the flight stabilization via drag.

I just started a thread on Castboolits yesterday and am getting some good info from a guy who has been screwing with slug design for a long time. Started off as me asking about wads for full bore diameter slugs. Current discussion is making me think I might go with the first design + drag disc as he said in his testing the slug in a shot cup worked as well or better than full bore slugs. However that being said I might take advantage of the ability to create a smaller diameter slug guided by the fins as well and pursue this design a bit. Either way the principle of a solely fin stabilized slug is dead as it is impossible to get enough stabilization in the vacuum/turbulent flows behind the head of the projectile without drag stabilization.

http://castboolits.gunloads.com/showthread.php?p=1292766#post1292766
 
Freyr_255 said:
... the principle of a solely fin stabilized slug is dead as it is impossible to get enough stabilization in the vacuum/turbulent flows behind the head of the projectile without drag stabilization.
Click to expand...

Well, it's probably significant that there are no fin-stabilized slugs commercially available. There would certainly be a market for them (even if only on the geewhizübercool! table).

There are indeed 12 ga fin-stabilized rounds out there, but they are either really complex HE rounds (almost pointless) or else plastic carrier loads with a liquid payload like tear gas or dye.

On thinking about it though, you could probably do it with a very long plastic tail fastened onto the base of a lead slug, tapering from full-bore in diameter at the join to slender at the end, with full-bore fins at the back. It would look like a mortar bomb (the shape is a proven one).

It would have to be loaded into a very long hull. Mortar bombs have a 5:1 length to bore ratio at best, making this, even at 4:1, close to 3" long. So maybe - maybe - a 3½" hull?

It would need some sort of buffering to prevent the tail from crumpling when fired.

Moreover, I suspect that, while practicable, it would not offer much by way of advantages over the current range of slugs.
 
ATOM said:
Well, it's probably significant that there are no fin-stabilized slugs commercially available. There would certainly be a market for them (even if only on the geewhizübercool! table).
Click to expand...

Are you saying 'the geewhizübercool! table' doesn't translate into killing power and superduperluper flight ballistics?....I would need a minimum of three peer reviewed studies before I believe that this is true. :p

Anyway here is the next version. I went with a 0.60" mass and a 0.68" flare. I'm debating right now if this is enough difference in diameter to impart any advantage to flight ballistics. If I had a 0.730" base and 0.600" projectile I would say its definitely good, but the 0.080" difference I'm a little iffy on.

Nuke20.jpg


Side note: I dropped the design down to fit inside the petals of a plastic wad again because Longbow over on Castboolits has done extensive testing of slugs and said that he feels there is no advantage to a full bore slug that a plastic wad fit doesn't have as well. Which makes sense...as long as it doesn't rattle down the bore does it really matter what is holding it stable? From what I've been reading most random s**t actually happens at the forcing cone to cause accuracy problems on the firearm end of things(based greatly on Longbows data). The rest is flight ballistics/aerodynamics.
Longbow said:
I forgot ~ you might also consider a wad slug size too at about 0.680"/0.685" diameter. So far I have found it easier to get good results using standard plastic wads rather than bore size slugs. I think it is due to the wad providing some support and guidance through the forcing cone.
Click to expand...

Anyway the question now is a 0.080" diameter difference significant enough to merit this slug design or should one increase this diameter difference by decreasing central mass diameter. If I look at it as a comparison to a Lyman wadcutter this design should have improved ballistics as it has a better nose profile and the larger base vs head should provide some measure of additional drag stabilization. I guess the question is, at bullet velocities how significant is 0.08"? I'm thinking it's more than I give it credit for meaning I'm good. At the same time I would like a larger difference to impart greater stability(and if I'm lucky overcome the transonic flight problem of bullets...doubt that would happen though).

If I did this with the 1oz design it would be a much greater contrast of 0.530" head to a 0.680" base. Bit up in the air as per usual.

*edit*

Split the difference. Design is now a 0.56" central mass with a 0.68" base flare. Gives a 0.12" contrast between head and tail which I think is a good amount. Weight should ring in around 1.25oz/547gr/35.4g. Looks more or less like the one above with a hair shaved off the main body.
 
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Loki610 said:
Looks like a fun design! make sure you bring some home with you once they get made and we'll test some out on a few gophers!
Click to expand...

But what about my new 375 H&H??? I got some Hornady 300gr DGX while I was in town today for the simple reason they had them(plus you never know...bison skull is pretty dense..). Perfect for gophers. Nothing like a copper clad, steel jacketed, expanding bullet to vaporize small rodents. :D

But ya, as an update if I don't think of some reason to alter this design I'm going to submit it tomorrow and see what the response is. Depending on price I may order some extra molds to pawn off to interested parties. ;)

:cheers:
 
Ceska said:
Very interesting project. Thanks for sharing Freyr, I hope this works out.
Click to expand...

Thanks. I sent in the latest design so we'll see what comes of it. I'm hoping they don't run into issues with making a mold and that it isn't too prohibitive in cost. *fingers crossed*

If it turns out well I'll probably get a run of them done to sell if people are interested(more because I like to share than anything). I'm thinking that since I'm getting Lee to make them that they will be able to mass produce some cheaper than a solely custom mold as they do give price breaks at 25(no set up fee) and 100 molds(dealer pricing). The big question at the moment is how much it costs to CNC a mold, which I'm waiting on a response to. Lathe boring in bulk by them is fairly cheap so we shall see.
 
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