Help me design my custom foster slug

[Jumbopanda]

I just bought a Lyman 12ga foster slug mold, and I'm looking to have it modified to cast bore size slugs by cutting one or more bands in it. But I'm concerned about the fact that any modifications can change the center of mass and center of pressure of the slugs, thus resulting in questionable stability of the projectile in flight. Also, I don't want to increase the mass of the slug too much, because I'd like to be able to use 1 1/8oz load data. I modeled the slug to the best of my ability in Solidworks, as well as ideas for potential mods to it. But honestly I'm not sure which one would work the best. I think a single band cut right before the ogive would be good because it results in a minimal change to the slug's center of mass. But a part of me thinks that a single band may not align the slug in the bore as well as two or three bands.

These are going to be shot out of a smoothbore only!


From left to right:


Original Lyman
Center of mass: 0.3823" from nose


Single band mod
Center of mass: 0.3837" from nose


Two band ogive mod
Center of mass: 0.3779" from nose

http://i.imgur.com/KMI2bBi.png

[elvas]

Either the one one the left or the one on the right. Center of mass and weight could be adjusted by making new core pins.

[Hogtamer]

That certainly looks promising as it may overcome the undersize problem, but It does nothing to overcome what longbow has identified a huge problem....thin skirt distortion on the hollow base.

[Jumbopanda]

That certainly looks promising as it may overcome the undersize problem, but It does nothing to overcome what longbow has identified a huge problem....thin skirt distortion on the hollow base.


Do factory foster slug designs suffer from this problem as well?

[Ballistics in Scotland]

Either the one one the left or the one on the right. Center of mass and weight could be adjusted by making new core pins.


More to the point, perhaps, the skirt could be thickened up by means of a reduced and more conical core pin. I can see no reason why a bore diameter (or VERY slightly larger) slug couldn't be used without a wad, like a minié ball. It needs to be one way or the other - either no wad or a really solid one, that won't get partly and probably asymmetrically crushed into the base cavity.

I can't see that the sort of differences you describe in location of the centre of mass would make a great deal of difference to stability. What perhaps might would be grooves in the rear part of the slug, that present more drag if the slug turns to present them more to the airflow on one side. The snag would be whether you could do that deeply enough without having a skirt that would tear at the groove.

If I was setting out to make a slug of this description, I don't believe I would use a mould at all. Or at least any mould, even improvised, which produces a chunk of lead of the right weight. I would turn or ream a stout steel cylinder of the bore diameter, and punches to fit one concave and one convex. A large engineering vice or heavy hammer would exert enough force to swage the slug from soft lead.

A bore diameter slug would need to be treated in some way to prevent leading, but it isn't the most demanding application in the world, and the threads on powder coating, tumble lubing etc. would be worth studying.

[longbow]

Yes, factory Foster slugs do suffer from the same issue. Every Foster slug I have recovered (mine as well as those others have shot) have crushed skirts and many have wad impressions in them. I am becoming convinced that the way the factories get decent accuracy is their wad column.

I have been told that the Lyman Foster slug can be made to be quite accurate by using a solid wad column with a copper or brass washer on top of the wad column so there is no give there and the slug is forced to obturate evenly to fill the bore. I tried that and failed but I do know that the slugs do obturate to fill the bore if they are cast of soft lead. I have recovered several slugs I cast, loaded and shot into deep wet snow. They were shorter and fatter than when they started out, but each one had obturated unevenly.

If you want a proven design as a basis, look at turbo's design bikerbeans is using. I believe turbo had Brooks make his mould.

If you want to modify the Lyman mould I would add 3 or 4 relatively narrow driving bands and make the O.D. a thou or two over you bore diameter. That will not change your center of mass enough to worry about, if any, and as has been stated the core pin can be altered to restore the center of mass if necessary by shortening it or tapering the end a bit.

You can grease or tumble lube if leading is an issue.

As for skirt distortion, I believe turbo's design has a thick enough skirt that it may not be a problem. If so then they can be cast out of wheelweights and heat treated.

Take that for what it is worth considering that I have pretty much failed at getting any hollow base design to work for me.

Longbow

[Jumbopanda]

Where can I find turbo's design?

[Jumbopanda]

This design would bring the COM to 0.3915". That may not seem like a big difference, but the slug is only 0.805" long, meaning that the COM is getting very close to the midpoint. I don't know where the center of pressure is, but I can only assume that it's pretty close to the midpoint. I've tried making modifications to the core, but nothing seems to change the COM by more than a couple of thousandths of an inch.


http://i.imgur.com/DZ6lgTa.png

[Greg5278]

Jumbo Panda, I have a Lyman mold modified as You have shown. It works okay, but wads still blow into the Hollow Base. I also have the Rapine 735600, which is heavier and a bit thicker. I put a Polypropolyene Ball in the Base to keep the Cards from deforming the Base. You can also Heat treat the Slug if needed. The Factory Slugs all shorten, and slug up when fired, as they are almost Pure Lead. I have fired the Rapine at up to 1555FPS, and it works pretty well in an open sighted High Standard Shotgun.
Greg
AKA 12 Bore
http://i.imgur.com/DZ6lgTa.png[/QUOTE]

[Cap'n Morgan]

Any front design other than flat-nose will move Center of Gravity to the rear. The ideal core length will be right on the CG point. Too short a core will add weight behind, too long will remove weight from front. Both scenarios will move CG further back.

[victorfox]

I'm just the village idiot, but the "key thing" in the lee seems to be quite useful (never shot or used them, I just live down there close to hell) and would not be too hard to implement. Like using splitting the bottom core pin? Or I'm just playing the idiot I'm?

[longbow]

Post #6 here:

http://castboolits.gunloads.com/showthread.php?261267-10ga-foster-slugs&highlight=turbo

A proven design that is working well for bikerbeans in 10 ga. I am pretty sure that is the same design turbo had made in 12 ga. too but he is not responding so we have what we have. I've tried to get hold of him but no go. I didn't search further but you can spend some time using the search function to look for posts by turbo1889. Lots of good info.

I have found the same issue with HB slug design. It is tough to get a really weight forward design with heavy skirt. The CG always winds up just about 50% or a bit further towards the nose. I've messed around with lots of 3D design and really made little progress that way. That is one of the main reasons I keep struggling to get a good attached wad design put together.

Not sure just how well the Lee Drive key works in comparison to a "filled" HB slug. Hot melt glue doesn't weigh hardly anything and does a good job of keeping wads out of the cavity. I've launched enough lead downrange that I won't be running that test.

I've got a couple of HB designs and a couple of attached wad designs yet to test and if not successful it is back to the rifled choke tube project for me. If that doesn't do it then I will concede defeat and go with fully rifled gun... or accept the accuracy limitations I have run into.

Longbow

[Ballistics in Scotland]

I understand the problem. If the skirt is thick enough to avoid partial collapse (if there are wads) or being expanded too tightly against the bore and tearing off (without wads), the weight distribution becomes inadequate for nose-forward stability in flight. I don't believe filling the cavity with hot-melt glue would help very much with either condition, because it is quite resilient.

There remains the possibility of filling it with something hard. One way of doing this would be with a hard wood or plastic plug which closely fits a tapered base cavity at the sides, but not at the bottom. This would, on firing, expand the slug to bore diameter and stay locked in place all the way to the target. This system was used in the early minié bullets, with a wooden plug or steel thimble, until it was found to be unnecessary. With or without wads would probably both work.

The other way would be if the plug was a forward extension of a solid wad, and made contact with the bottom but not the sides of the cavity, and not with the rear edge of the skirt. The idea would be for it to detach on leaving the muzzle. I think this would work well if turned from wood, with the grain oriented along the bore.

Another idea is suggested by the mention of a brass washer to prevent uneven extrusion of the wad into the base cavity. Suppose a hole were drilled through the centre of the wad? In theory this could be just big enough to allow enough pressure to expand but not overexpand the skirt. I don't much fancy risking my health on that theory, though. But acting on the centre and not the edges of a hot-melt or other resilient cavity filler might do just what you need.

Congratulations on your escape from your shotgun explosion. All the best authorities I know have found that the great majority of people end up injured little or not at all. But it isn't the sort of thing you would want to count on. A lot of very knowledgeable 19th century designers arrived at the short-step chamber, around the time the shotgun was perfected. I don't think the long throat is of much advantage with shot, and with slugs we should avoid both this and cases shorter than the gun is chambered for.

[Hogtamer]

Do you believe this?
http://castboolits.gunloads.com/showthread.php?247074-200-yd-Sabot-target!!!
None of you really know me, so I could be an inveterate liar, lunatic or just plain lucky. The problem for me is I know this happened, with a witness even, at his homemade range on his bench! The guy worships me! But for some reason I cannot reliably, repeatedly, replicate this. Seemingly the same loads, same guns, just that sometimes I can get results like this and sometimes it's barn door accuracy. This was last July, sweat running in my eyes, barrels smoking hot, the bench was rickety, all the things that would promote awful shooting. Sort of like longbows last testing with loads that had done well before but awful now. So I'm wondering....is the problem more about the inherent imprecision in components like wads and liberal shotgun tolerances, loader variations, slight variations in alloy, different rigidity in hulls....the list is endless. I know that in one session last year I found the perfect load for my .270 A-bolt rifle using a lee whack-mole loader, a different bullet and a 1/2 grn powder difference. 2 weeks ago went out and the only reason I miss is a 2" circle @ 200 yds is the fact that my crosshairs cover the circle or failure to dope the wind just right. Nothing has changed! The point in this long post and venting of frustration is that perhaps I focus too much on the slug itself and not enough on the precision of components, wad pressure, crimp and loading techniques. I swear that Lee 7/8 slug load has been amazing, but today it just might make a liar out of me. Friends and fellow loaders I ask, WHY?

[longbow]

Hogtamer:

I believe you!

I find that shooting sessions do show significant variations even beyond my limited competence as a shooter. There are indeed a lot of variables and one I certainly do not pay enough attention to is hulls and hull condition. The last outing was with Federal field hulls with paper basewads where for the most part I have been using Fiocchi hulls in the past. Their lifespan has expired though. Now logically I should buy some more but my frugal nature (counter productive though it is) dictates that once fired Federal hulls should be fine. Well... maybe not! That and the fact I fold crimped this time where I usually roll crimp. Would that make the difference form darn good/pretty good groups to "Why bother?" groups? I wouldn't think so but...?

These are the reasons I have not been satisfied with my results because unless I can shoot approximately the same group at the same distance on demand, it is not dependable.

I have shot a couple 100 yard groups with 0.735" round balls that were about 6". Yea! I'm done... Except next time I get maybe 3 together and 2 some 8" or 10" away (or maybe more).

So far for home loaded slugs AQ's have done the best for me and even then I was limited to one box of 25. How repeatable would my results be if I bought another 10 boxes? I think pretty good but...? I have not seen Brenneke slugs for reloading for many, many years but I would expect them to do well too.

Gualandi DGS slugs shot pretty well but out of the few I had one keyholed and the two I recovered actually showed poor skirt performance so...?

I am interested in the brass and steel slugs being used in Europe mostly because they seem to shoot very accurately, I think due to total consistency of a machined slug and solid consistent wad. The same design in lead would be very heavy but may well be worth trying for the consistency factor. Note that I believe small inconsistencies (some very small) add up to significantly inconsistent accuracy.

I am stating the obvious here and I have few to no good answers.

I think it goes without saying that a full bore slug or ball in a fully rifled gun should provide reasonable and consistent accuracy. However, smoothbores, well, I think there is a bit of black magic in getting good and consistent results.

And you said your post was long!

Longbow

[Ballistics in Scotland]

I have, once in a while, seen some assertion on the boards supported by test results which the laws of science suggest did not actually happen. I believe Hogtamer, though. It is just that a three-shot group is far, far less than half as good evidence as a six-shot one, and anybody looking for compelling evidence would do better to try ten shots.

That perfectly fits what he tells us, that that 200 yard group with the Hubel Sabot slug was a freak he can seldom equal. The 100 yard group with the Lee 7/8oz sabot is much more like what a person might often but not always obtain. That is more like what is true of well-designed slug loads in general, rather than specific brands.

For the rifle, it could be better to dispense with a black aiming mark altogether, and use a white square of about 3 of 4in. side, or four which lines arranged like an unstarted noughts and crosses game. The eye is very good at determining whether the cross-hairs are centred in shapes like that.

[Y-man]

...For the rifle, it could be better to dispense with a black aiming mark altogether, and use a white square of about 3 of 4in. side, or four which lines arranged like an unstarted noughts and crosses game. The eye is very good at determining whether the cross-hairs are centred in shapes like that.

Hi, this is interesting to me: I plan to go testing .729" 12-ga Round-balls [Jeff Tanner Mould] on a 24" Rifled Barrel on a Mossberg 500A for the first time in Early June. I am shooting load replacements: target shot replaced with round-ball of SAME weight on doughnut felt and had plastic wads.

I will be using a Bushnell TRS-25 Red Dot, and my REALISTIC max aiming point will be 50 yards/ Groups of 4" - 3-rounds each.

My question is suggestions as per TARGETS: I plan to check my POA/POI by:
1. Using a rest, or shooting stick and maybe even firing prone [I have to go out to our farm to shoot: no ranges here! Perfectly safe: beyond the farm is a lake of up to 4 kms long.]
2. I will use a reflective board [Which I have fabricated already] to zero onto paper using a Sightmark Laser Bore-Sight, first. [I have tested this, and it works, even in bright daylight. out to 30 yards.
3. I will have a main target of A4 size paper, stuck on a wood board of maybe 3' by 3' size [To see flyers properly.] Each group of shots will be marked with unique marker colour.

I look forward to this [Longbow too has been anticipating this!] and will update once done: but BiS - What do you think of the planned test set-up?

[No chronograph or other equipment available!]

[Cap'n Morgan]

Hogtamer.

The thing is that a good three-shot group could be a fluke, but a bad three-shot group is certain proof the load won't shoot. Even going from five shot groups to ten shots will statistically increase group size by a third. Gaussian distribution is a funny thing...

[longbow]

That's why I am still bruised and punchy from my last session. I load 10 of each and shoot at least 5 at paper. If the 5 don't show any promise I stop... sometimes. If they do show any sort of accuracy then I carry on.

I need a heavier gun, more padding and something to keep my brain from rattling.

I don't know squat about Gaussian distribution but I know that when I shoot more rounds my good groups tend to get not so good. And when I shoot more groups often the same thing happens. What started out good may turn out to be mediocre or poor.

Of course when shooting slugs from a bench one should add a flinch factor to the mathematics as well.

Not helping the OP much at this point.

Longbow

[Ballistics in Scotland]

What I said about a square white aiming mark applied to a crosshair sight. With a red dot circular would probably be better. The use of a laser boresighter seems a good idea. Some chambers will be a bit large for precise alignment, but it could be centred up with a thickness of tape all around.

You would probably find prone shooting quite punishing with heavy loads, and the smoothbore ball gun isn't really precise enough to need it. Sitting with elbows on knees should be fine, and more useful practice for the hunting field, when you will often need to see over grass. Various people have commented that round ball loads aren't at all bad, provided that you can prevent them from rolling in the bore.

[longbow]

Good round ball loads do very well in my experience. I have shot few other slugs that do as well to 50 yards or a little further. Much beyond 50 or maybe 60 yards though groups do tend to open up. I have never tested mine in 10 yard increments to 100 yards though so can't say just how far they are consistent to.

Out to 50 yards I can usually depend on 3" to 4" groups with both round balls in shotcups or naked 0.735" ball on a hard card wad column.

I can say though that the 0.735" round balls do tend to roll into the bore because I have recovered several with skewed "belts" around their equators. A donut wad, inverted gas seal or a scoop of COW should help avoid that... as would 3" hulls in a 3" chamber I am guessing.

In general I lean towards a 0.662" or 0.678" round ball in a shotcup as they are easy to load and shoot very well. The shotcup of course eliminates any chance of rolling in the bore.

After my last range session shooting 50 slug loads from the bench I flinch even thinking about shooting them prone. Yikes!

Longbow

[Ballistics in Scotland]

Ah, that is worth knowing, about the tight and therefore belted ball rotating. But I think it would take the form of just shifting a little, and be nothing like as harmful as one that enters the outside air rotating.

It is worth considering how rotation in the air makes the ball deviate. Say the rotation is clockwise, the apparent velocity of the moving air is velocity plus speed of the rotating surface on the 9 o'clock side, and velocity minus speed of the rotating velocity on the right. This produces extra pressure on the 9 o'clock side, and the bullet deviates in a three o'clock direction. If the rotation arose from curvature of the bore (far from unknown in the musket days), the deviation is exactly the opposite of what the laymen would expect.

I think, though, the latter only happens if the ball fits the bore loosely.

In your case it would take quite a bit of force to deform lead. My guess is that a hard card wad tilted. With all that people are doing with plastic wads, you would think that a wad with a hemispherical recess could be made. With shotguns required for deer in so many jurisdictions, there is surely a demand for anything that improves accuracy. From the makers' point of view injection moulding and mould making both involve expensive tooling, but a mould is a once in a lifetime process, and wads aren't.

General Hatcher claimed that a round ball, some way downrange, slips out from behind the cushion of air which builds up in front of it. He compares it with the spit ball in baseball, but I don't quite know what that is. It sounds rather horrid. It explains why the ball's path is more hockey-stick shaped than a spinning bullet's, with a lot more deviation in the second fifty than the first.

Now to go from his authoritative diagnosis to my conjecture, it may be that that cushion induces a roll in the air, and that rifling-induced spin acts like a tiny centrifugal pump, throwing off that air to all sides equally. Single-tub washing machines used to have a wheel with only shallow ribs, and yet threw up great turbulence in the water. I think friction would do the same with a spinning bullet.

[Greg5278]

Well, if Someone wants to share the cost of testing some Lathe Turned Slugs, I might be able to Help.
I have the 773gr .729" Diameter copper slugs just waiting to be tested in a Bench Gun. I'll provide the Slugs for Tom Armbrusts Canon if Somebody else pays for the Test. His Setup takes the Human component out of the Equation, and will give the true Accuracy potential.

Greg
AKA 12 Bore

[longbow]

I've been wanting to see results from these since you e-mailed me Greg. It seems that design is pretty popular in Europe. I see you have gone the full bore route rather than sub bore in a sleeve.

What is the cost of the test?

I thought about turning some from lead but they would be awfully heavy even in sub bore size. Zinc might be a good candidate for that style of slug and produce a reasonable weight. In zinc they could be cast.

BIS:

The 0.735" round balls I recovered look as though they started out with a roll possibly from opening crimp, tilting wad, catching the edge of the forcing cone or entering the bore off center. They did not spin in the bore but rather were stopped from spinning by the bore.

As for spinning in the air, any slight roll will get worse because of uneven air flow and any distortion in the surface of the ball will cause drag resulting in a spin which will get worse and worse.

I have heard the trajectory being described as a "trombone" trajectory meaning that for the first part of the journey the ball stays more or less in line but as it picks up spin so the trajectory deviates more and more rapidly. In fact one poster on All Double Guns (IIRC) said in certain light conditions you can see the balls fly and observe the trombone trajectory.

I have never seen it but I can say that out to 50 yards balls can do very well but much beyond 50 yards things start to deteriorate quickly. Some patch ball smoothbore musket shooters do well to 100 yards and are competitive with patch ball rifle shooters. Those balls would be started out with virtually no spin if properly patched so highest chance of retaining accuracy further.

The baseball analogy is describing a thrown curve ball which has a spin intentionally put on the ball so it will change direction on its way to the batter.

Use a loose fitting round ball in a smoothbore and you can miss a 2' x 3' target at 50 yards (ask how I know).

Longbow

[Ballistics in Scotland]

Same way I know, probably, although I want it read into the record that it was somebody else's gun.

Military muskets were often very badly bored, for nobody got to look through them from the breech. I doubt if they were consistent enough in bore diameter to issue everyone with close-fitting balls. But a lot of very clever minds gave up on making anything else the ordinary infantryman's issue, until the Minié bullet came along. Even George Washington tried to make his men adopt smoothbores muskets. A lot of people forget how the eighteenth century battlefield was obscured by smoke. A battalion appearing out the smoke could fire at fifty yards, and if only one side could load and march fast enough, they alone could deliver a second volley at ten or twenty. At that range Brown Bess was as deadly as any firearm ever made.

It is possible to see a rifle bullet in flight - the old .450 target bullets in particular, but probably also .30 caliber. The snag is that it has to be an observer very close to the shooter, but not the shooter himself, and you have to train yourself. If the light is good and you know exactly where the trajectory will take it, you ought to see at least part of its flight.

[longbow]

I freely admit it was me with my gun and more embarrassingly, more than once!

Yes, smoothbore muskets are a good comparison. Not only could they have varying dimensions and bore finish as you point out, there was excess clearance left intentionally to allow fast loading even when the bore was badly fouled. Accuracy was secondary to slinging masses of lead downrange in volley fire.

I think overall ranging the enemy and lobbing big 'ol .75 cal. round balls into their midst was the goal much like clout shooting with long bow ~ get the range and drop arrows into the "herd". Getting hit by a .75 cal. round ball would most certainly leave a mark! I'll pass thanks, I have enough trouble on the butt end of a slug loaded 12 ga.

I have never seen a slug or ball in flight but I have to think that with the sun behind you and looking down the sighting line while someone else shoots you would have a good chance. It would be interesting to watch a round ball and its trajectory. Of course it could be intentionally loaded to low velocity too which would make it easier. And that is a thought I should try.

Longbow

[Ballistics in Scotland]

It would probably be easiest with the round ball, and difficult with a Forster slug, which has a rear end where the sun don't shine. Here is a device which might be of help to anyone interested in what happens to a projectile in flight:

http://www.cameraaxe.com/

It is quite ironic that the skilled bowman achieved accuracy far superior to the military musket as usually constituted. General Hanger, writing in the early nineteenth century, said that with an individual enemy at 200 yards, you might as well fire at the moon. But you would not want to stand that close to a bowman who fought at Crecy, and they brought 600,000 arrows to the battlefield, with an efficient battlefield distribution system. The snag is that it took a lifetime to make a bowman, with a bow more powerful than most modern competitive archers could draw. Sherlock Holmes would have had trouble working out the reason for their distinctive musculature.

During the Revolutionary War Benjamin Franklin advocated arming regiments with the bow, and quoted in support "our great victories against the French." That was a very interesting phrase to use, when you think about it, and evidence of how well the American Revolution fitted into the British pattern of revolts and insurrections which produced parliamentary democracy. I do no think he was talking pre-Columbian.

[00BuckOperator]

Check out A.S. molds. Website or on Facebook! They make a .729 Foster & .729 Pellet Mold. Best mold maker ever. I have a lyman foster also and it drops at .699! What a joke

[iomskp]

Have a look at Cast Bullet Engineering, I have had one of his moulds for years I use the slugs in my 12 bore rifles, they work very well

[JBinMN]

Just so ya know, before these last 2 posts, this topic last posted to on 05-25-2015, 09:07 PM.

;)

[a danl]

don' t worry about a thin skirt if you fill the hollow as i do with beeswax that way it gives you a solid base. i also use an overshot card just under the slug to keep the next wad from sticking to the wax. also i saturate the next wad with bore butter which eliminates all leading. it's interesting how our minds keep working on how to solve all our problems