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

[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.

[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
[/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/show...ighlight=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/show...d-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.