12 gauge slug design

[hkr]

I'm going to try to make some copper and brass slugs on a small mill I have access to using it as a lathe. I would appreciate suggestions on the design. I'm not going for long range performance, just good penetration in a tough target at close range, so I thought something similar to the Brenneke would be a good place to start.

Are the lands (raised parts - not sure if that's the correct term when talking about a projectile) necessary if my shotgun doesn't have a choke?

Here is a quick sketch of what I was thinking. Except I just realized it shouldn't have a pointed tip like I drew or it could set off rounds in the tube.

 

[LUTNIT]

If you are using copper or brass you don't want to have a choke at all. The "rifling" on lead slugs don't actually cause any spin and are just there to compress if there happens to be a choke. If you tried that with a solid copper or brass slug that was bore diameter I wouldn't want to be standing anywhere near you.

Copper and brass wont expand with the hollow base to fit the bore as well as lead for a good seal so a plastic gas seal wad or some such would be required. The hollow base of course adds drag stability in flight but I don't think it would serve double duty as a gas seal like solid lead hollow base slugs can.

I would just make the outside of the slug a few thousands smaller than the bore diameter and test it for accuracy. Perhaps make it even smaller and add a sleve inside the shell?

The pointed tip is fine and wont set off rounds in front so long as the entire slug is contained within the hull (which they normally are). If part of the slug is sticking forward then yes it could cause a chain fire in the magazine. You could use a star crimp instead of a roll crimp to add further protection but many people say this causes problems with slugs.

 

[hkr]

Ok well that makes it simpler then if I can make the whole slug just under bore diameter. Good point about the base not expanding I hadn't thought of that. I wonder if making the very back edge extra thin would compensate for the harder material.

Here is a model done in solidworks. 1 1/4 ounces like the foster slug I want to compare it to.

I don't want to invest in reloading stuff yet in case these don't turn out. Could I safely replace the slug in a factory cartridge as long as the weight is exactly the same so that the powder would generate the same pressure? Or would there potentially be a difference in friction in the barrel that could lead to a pressure spike?

 

[just having some fun]

Lyman makes a very nice Pellet gun type slug and there is reloading data for it
it can be used in riffled barrels, IC and maybe modified choke

 

[joedude]

Could I safely replace the slug in a factory cartridge as long as the weight is exactly the same so that the powder would generate the same pressure? Or would there potentially be a difference in friction in the barrel that could lead to a pressure spike?

That should be just fine. Many people (myself included) pour out the birdshot from target loads and melt them into slug moulds to make low recoil slugs. I do it just for fun. Never had a problem and never heard of anyone else having a problem.

FYI when I re-insert the slug in the shell, I place it in the wad. That way the slug never touches the barrel. Also, as the wad would keep all the birdshot together when it is fired, it acts as a solid projectile until it exits the muzzle and separates. Therefore if you fire a solid slug of the same weight from the same shell, you should have comparable pressures.

 

[1shot]

First of all- are you firing it from a choked barrel or rifled barrel?

When not use your more simple design and make the outside diameter .680 and put it in a conventional shot cup?

I'm currently playing with my own cast slugs and roundballs, its interesting and rewarding..

 

[tbrwlf]

I cast the lyman slugmaster wasp waist slug. 1.25 oz of pure lead will knock down anything it hits. It looks like a very large pellet for a pellet gun.

If you want I can send you a couple and you send back a couple of yours.

PM me if you are interested.

 

[ATOM]

If you are using copper or brass you don't want to have a choke at all. The "rifling" on lead slugs don't actually cause any spin and are just there to compress if there happens to be a choke. If you tried that with a solid copper or brass slug that was bore diameter I wouldn't want to be standing anywhere near you.

The slug is, as you note, stabilized by flare stabilization; the skirt acts like fins to keep pushing the tail back in line. The 'rifling' will certainly not impart enough spin to give gyroscopic stability like a rifle or pistol bullet. It will however give a slight spin, which helps to some extent in correcting flaws in the projectile. Let's say a projectile is a bit 'off' and would naturally tend to drift to, say, the left. The trajectory of the round (not counting drop due to gravity) will increasingly be to the left of the line of sight. If the slug has a slight spin on it, it will spin around the line of sight in a spiral. Not perfectly accurate, but better. Minor effect, but one that should not be overlooked.

I completely agree with your comments on a solid copper or brass slug.

 

[hkr]

The barrel is a 14" smooth bore with no choke, measures 0.729 - 0.730" diameter at the muzzle. I am designing this round for use at not more than 30 yards, so I'm going to skip the rifling because the rotational path correction won't be as relevant over that distance and it's a heck of a lot easier to make since I don't have a 4 axis mill. Also I don't have any rifled or choked barrels at this point so no risk of making that mistake.

I suppose I could make it a bit smaller and put it in a shot cup, I hadn't thought of that. I was planning on just replacing the foster slug in some federal 3" shells I have because they deliver the most energy of any shells I could find with some quick searching (1 1/4 ounces/550 grains @ 1600 fps). There is a plastic wad so that should take care of sealing.

I guess the pellet gun type slugs would have more stabilization for the same center of gravity as a straight sided hollow base, because the angle of the skirt would catch the air more. I think I'll try this for now though because the simpler the better from a machining perspective, and just check for keyholing when I test them.

Speaking of machining I made some chips tonight, but didn't quite get the base done and still have to figure out how to do the nose. Here's a preview:

If I were to get a press so I could reload properly, and have the option of changing the slug weight, would there be higher penetration for the same amount of powder if it weighed more? So heavier but slower? I'm confused because looking at the range of shells out there it seems like the heavier loads have lower kinetic energy, but I think they might have more momentum?

 

[legi0n]

A heavier projectile will require less powder (everything else being the same).
Read some internal ballistics book before delving in experiments. (brief: the heavier slug has bigger inertia and will start moving slower. This in turn will increase the initial pressure spike in the shell (or case) which in turn will make the powder burn faster and increase the pressure even higher. Again, everything else being the same.
A heavier projectile will therefore have less kinetic energy but will hold it longer.
There's an optimal bullet weight (or narrow range of weights) for each caliber that's the best compromise between velocity, trajectory and range.
But then again, the shape of the projectile is also a big factor and so is the projectile fit to barrel.
It's not a simple task to design your own shells or rounds.

 

[LUTNIT]

when I re-insert the slug in the shell, I place it in the wad. That way the slug never touches the barrel.

Do you use a Lee mould?

I use the Lee 1oz key drive foster slug mould and find it only really works when a shot cup is used. It is quite a bit under bore diameter and when I tried some with the pedals cut off the wads and the groups opened up at 25 yards (only range I tested at.)

If I were to get a press so I could reload properly, and have the option of changing the slug weight, would there be higher penetration for the same amount of powder if it weighed more? So heavier but slower? I'm confused because looking at the range of shells out there it seems like the heavier loads have lower kinetic energy, but I think they might have more momentum?

Two objects of different weight travelling with the same energy will have different momentum's with the heavier one being higher. If you reduce the energy than you reduce the momentum as well. Momentum makes the slug less effected by wind and often has more "knock down power" as many people say. I'm not sure on the advantages/disadvantages of reducing energy but increasing slug weight as I have only ever tested stuff with 1oz slugs. One thing I can think of is that if the projectile has less energy it will deform less when it hits the target? Reducing velocity with a heavier projectile but keeping the energy the same to increase momentum has it's uses but reducing the energy only really reduces the recoil as far as I know.

A lot of people look at projectile weight and relate that to "power". They buy ammo with heavier projectiles to fire more "powerful" shots. I have actually been told by one guy that "muzzle energy" is a made up concept for marketing that has zero relation to real life physics and only projectile weight matters. Heavier slugs, even at lower kinetic energy levels, may be a marketing thing since a lot of people who shoot don't look at the science behind it.

Heavier projectiles with the same powder charge will create more pressure (possibly to dangerous levels to be careful and work up from lower charges to start.) The issue with penetration with lead slugs is you can put as much kinetic energy into them as you want but lead is still a soft metal that deforms quite easily. Brenneke type slugs aren't as hollow (if hollow at all) and are often pointed without a hollow point and that is how they increase penetration. The slug is able to hold together longer to keeps moving through the target as it is more solid and the shape prevents it from expanding as quickly.

It's exactly the same as the way FMJ bullets pass through targets that hollow points will stop in. The hollow point dumps its kinetic energy into the target in a shorter depth causing more damage in that depth but less penetration.

A solid brass or copper slug, especially pointed, will get far more penetration than an equal weight round or hollow point lead slug at any velocity/energy.

Personally I would stick with one slug weight and play around with powder charges to get the desired muzzle velocity/energy (within safe limits of course.) I'm pretty sure higher energy, regardless of momentum, will give better results in pure penetration of the target.

 

[hkr]

No it's certainly not simple, I think for now I'll just stick to the slug design and construction process to replace the slug in this particular shell. That's proving challenging enough, trying to manually write the code for this damn machine. And I'll do some reading as you suggested before experimenting with different powder and weights.

That makes sense about how momentum/kinetic energy and the type of slug relate. I was thinking that because my goal is to maximize penetration and minimize deflection, momentum and sectional density might play a more important role than kinetic energy, within reason. Kinetic energy disproportionally favours velocity over mass, whereas momentum considers them equally, which makes me think for penetration in a non homogeneous object (ie bones, fur and different tissue densities all at different angles vs. ballistics gelatin) the latter might be more relevant. I guess at this point in the project it's not too important because I'm holding that variable constant.

Another factor I should consider, though, is the shape of the nose. This model of a .410 foster slug got me thinking about it:

http://mcb-homis.com/slugcfd/slugcfd.html

I can see how the Brenneke style of cone with a wadcutter shoulder could work, the cone would initiate the the shock wave which would partially miss the shoulder, eliminating a lot of the drag associated with a flat front. But how much effect on velocity would this have over a short distance - enough to justify the extra work in making it? And would stability be affected? What about penetration? On a perpendicular impact it makes sense that it would help initiate penetration, but does that matter through the rest of the target when you have a sharp shoulder also cutting through? And what about an angled impact? In that case the shoulder is initiating penetration, and the cone could be parallel to the target, which might increase deflection. Too many variables! I think I need to just make a few different styles and test them.

I finished one but it got kind of messed up from coding errors and not a rigid enough mount. I went with the Brenneke idea of screwing the wad to the slug, because I thought it would save me a machining step but I think I'll have to have another step anyways to keep it rigid enough. At any rate I think this is the style I will keep it at, with improvements on the nose obviously.

 

[Freyr_255]

Brenneke style is the way to go for good stabilization. At closer ranges the hollow base works well enough as long as you have enough drag on the rear of the bullet. De-stabilization at longer ranges with hollow base slugs is due to a lack of drag due to decreasing velocity. Brennekes keep the drag high due to having a much longer profile and very light tail end(wadding).

IMHO I wouldn't do a full bore copper/brass slug. Too many things could cause you blow up your gun. The old military steel designs were like an hour glass with a lead ring on the outer edges to ride the bore with very good reason. If you under size it so that it will not accidentally wedge in the forcing cone or the bore you will get it rattling down your barrel and it becomes inaccurate. If you size it tight it will likely jam and blow up your gun.

For this style of slug I would recommend undersizing it to the bore and shooting it out of a shot cup. The shot cup will fit tight to the bore if you size it right(check petal thickness) and allow enough give to safely shoot these, in addition it should prevent any damage to the forcing cone as they act as kind of a funnel(make sure the petals extend about 1/8" past the edge of the slug). If you want to stick to the brenneke stabilization use a deeper shot cup and add felt wadding to the base of the slug. If you opt for a hollow base I would recommend tapering the base similar to how a pellet is designed. The hollow cavity on the side of the slug allows for greater drag and stability as it sucks the airflow in a bit before it hits the drag cone on the rear.

For nose design I like the truncated cone or similar.

Best of luck!



*edit*

Here is a thread I did last year on a slug design. It evolved drastically as I went and in the end I had what I thought to be a winner. I just ran into problems with getting a 2 part mould made for it as it required CNC milling to make. Final design was/is effectively 4 fins to ride the bore in a shot cup and allow air to pass on to drag disc, a central mass, and a disc on the base to stabilize. Longbow over on Castboolits.com was a great contributor to my knowledge base. I think it weighed in at a bit over 1 1/4oz.

http://www.canadiangunnutz.com/forum/showthread.php?t=615312&highlight=slug

*edit 2*

Net find of an image like I was describing above. Second from right...hourglass with lead rings. Third from right looks like it's meant to sit in a shotcup. Could be a decent design for you and should be easy-ish to machine. There is a commercial slug in the US made in lead with a similar design...like hell I can remember the name now. I'll try and find it. (found it: http://www.dixieslugs.com/products.html)

 

[hkr]

Thanks for the link to your thread, it was an interesting read. Have you made any progress on it recently? Sounds like we are after a similar end goal, just different paths.

I don't have a choke so I wasn't worried about making it full bore, but I suppose it's possible that the barrel might not be true the full length and I can't check that. Or I could forget to double check the diameter of one and have a very bad day. So perhaps I should use a shotcup or make a shallow band on either end that would be narrow enough to give if there was a constriction, like in my very first drawing. I don't want to do one of the narrow waisted ones because it involves a lot of material removal and the small machine I'm using is very slow. That's part of my challenge is to design it with limited machining capabilities.

How would you attach a felt wad and ensure it's centered?

Also, I plan on comparing these to a number of different shells on some sort of standardized target in about a month when I have more free time. So once I have some of these made I would be interested in trading a few of them to get my hands on any other interesting penetrating rounds you guys might have, hopefully including some real Brennekes. And I will post up the results with lots of pictures of course .

 

[Freyr_255]

Thanks for the link to your thread, it was an interesting read. Have you made any progress on it recently? Sounds like we are after a similar end goal, just different paths.

I don't have a choke so I wasn't worried about making it full bore, but I suppose it's possible that the barrel might not be true the full length and I can't check that. Or I could forget to double check the diameter of one and have a very bad day. So perhaps I should use a shotcup or make a shallow band on either end that would be narrow enough to give if there was a constriction, like in my very first drawing. I don't want to do one of the narrow waisted ones because it involves a lot of material removal and the small machine I'm using is very slow. That's part of my challenge is to design it with limited machining capabilities.

How would you attach a felt wad and ensure it's centered?

Also, I plan on comparing these to a number of different shells on some sort of standardized target in about a month when I have more free time. So once I have some of these made I would be interested in trading a few of them to get my hands on any other interesting penetrating rounds you guys might have, hopefully including some real Brennekes. And I will post up the results with lots of pictures of course .

Fair enough. The slug I was designing was initially intended to be like a brenneke for penetration then evolved into sort of a longer range hammer that could be dropped from a 2 part mould. I was kind of intending them to be simple to make(no attaching wads etc) and possibly get a whole run of moulds made for distribution. The problem I had with most slugs is they were either foster(crap design IMHO for anything other than light skinned game) or Brenneke requiring an attached wad which was not simple to make and required a custom mould.

If you don't want to remove much material then just do a cylinder like you have and machine it down 0.050 in the middle or so which will help with pressure should it be tight. I think most wads are about 0.02 IIRC. Some variation so give it a look.

For felt wads you can make up a jig by drilling a 5/8" hole in a board and dropping the slug in followed by a felt wad. Longbow on Castboolits.com developed one that was a slug dropped into a mold(think it was PVC pipe or something that was the right diameter). He then filled the back end up with hot glue making a hot glue wad held on by the screw(screw was per-attached, then filled). Supposedly it worked rather well.

My final post in that thread I mention I was going to look into steel slugs. Well what I did find out is that certain flare nuts/bolts have about the right diameter to fit down a shotgun bore with wadding(looked into washer diameters but didn't find anything workable....doesn't mean they don't exist though). I'll have to try and find the ones I had to remember what size they were though since it's been a little while. I was thinking about a 1.25-1.5" bolt fired head first with a flare nut on the back to stabilize. For added weight I was contemplating making a simple mould to cast some lead on the front end held on by the threads. Or a mould making a lead dough nut that I could thread on. Or just using additional steel nuts. Lots of ideas with it but I kinda had some crap happen in my life that put the brakes on this. I may pick up on it again this year if I can.

The above mentioned nut/bolt slug I think will work but I have no idea the accuracy potential as the tolerances on bolts and such are a bit loose. That being said for close range penetration I don't think it makes a lick of difference as long as it more or less hits head first. Hell even a sideways chunk of steel doing 1500fps is going to leave one hell of a mark.

 

[hkr]

Thanks for those last thoughts, I didn't respond because I had to put this aside for a while. But I managed to get out on Sunday to do some penetration tests, and took a bunch of pictures. I'll break this up into several posts because there are so many and I don't have time to do it all at once.

These girls were kind enough to lend their services in the name of science.

The lineup of ammo. From left to right:
-Brass slug in Federal 3" magnum shell ~515 grain ? fps ? ft-lbs
-RWS Exact 2 3/4" gualandi slug 492 grain 1362 fps 2026 ft-lbs
-Federal 3" Magnum foster slug 547 grain 1600 fps 3109 ft-lbs (for some reason I thought they were Remington when I was in the field, so you'll see that written on some of the targets)
-Hornady SST 2 3/4" sabot slug 300 grain 2000 fps 2664 ft-lbs
-Federal .270 Win soft point 150 grain 2830 fps 2665 ft-lbs
-Winchester .270 Win ballistic silvertip 130 grain 3050 fps 2685 ft-lbs

The targets were 6x6 capped with tile to simulate a very tough target at approximately 25 meters, both perpendicular to projectile path and at approximately a 35 degree angle. I know this isn't a very accurate analogue for an animal but I wanted to use material I had on hand and keep things relatively consistent. Broken tiles were replaced between shots, and most perpendicular shots were into a fresh end of wood.

These are the two rounds I was most interested in comparing, but I'm glad I tested the others too.

And here is an overview of the results. From left to right: Brass in Fed shell, Brass in RWS shell, RWS, RWS, Federal foster, Hornady, Hornady, Federal 150gr, Winchester 130gr.

Results for the individual slugs/bullets still to come, stay tuned!

 

[hkr]

FEDERAL 3" FOSTER SLUG

The slug glanced out of the 6x6 and got stuck between the stump's bark.

I forgot to take a picture from further back before I remove the tiles but this is the same end.

Quite the expansion, the slug pancaked! But it seemed to hold together reasonably well.

After several shots only getting hits on the edges (likely due to error or flinching on my part rather than a problem with the shells), I closed to half the distance and fired this one. Unfortunately either the slug turned to dust or fell out when I was splitting the wood, as I couldn't find it.

BRASS SLUG IN 3" FEDERAL SHELL

The round part in front of the slug imprint was caused by a cone of powdered tile that was highly compressed.

Minimal expansion.

BRASS SLUG IN RWS 2 3/4" SHELL

I decided to use a spare brass slug that I wasn't originally planning on firing, by putting it in a RWS shell.

The slug ended up coming to rest backwards on a bit of an angle. Likely tumbled in the air because of no stabilization, or was rotated on impact with the angled surface.

As with the other brass slug, minimal expansion.

RWS EXACT 2 3/4" SLUG

Perpendicular impact.

Angled impact. The first shot was centered and knocked the two pieces apart, and the slug wasn't recovered as it kept on going.

Further angled shots hit the tile as planned.

The recovered slugs had greater deformation from the angled impact than the perpendicular one.

 

[dthunter]

I shot some hard cast linotype lee key slugs.
I filled the hollow base with a muzzleloading lube to help prevent the wad from extruding into the hollow base and sticking to the slug during the flight.
This worked great. I got about 4" groups at 100 with my savage slug warrior.
The penetration into poplar was tremendous! 30" at least! Lengthwise in a section of log.
Dropped bears like a sack of "you know".
I eventually sold the slug gun because my shoulder was too bad to shoot heavy recoiling guns. And this slug gun certainly qualified as Heavy recoil.

 

[hkr]

HORNADY 2 3/4" SABOT SLUG

Perpendicular impact

Angled impact - Noticeably more slug deformation and less weight retention than perpendicular impact.

FEDERAL .270 WIN 150GR SOFT POINT

WINCHESTER .270 WIN 130GR BALLISTIC TIP

 

[unstableryan]

a heavy hard cast 45-70 loaded to 1500 would penetrate farther than any of those.