New slug design

[longbow]

Good to see you back at it again Cap'n!

Looking forward to range reports.

[BigMrTong]

Same, excited to see the results on these new ones

[centershot]

Well, I'm finally getting ready for round three with my latest slug design.

The previous design, while accurate and stable up to about fifty yards, it would hit the target sideways at longer ranges. I decided to go with Hogtamers suggestion of a faster load - preferable around 1500 fps to keep the slug supersonic for as long as possible.

To accomplish this the slug had to be lighter - alas, a new mold had to be made. The new slug is much lighter - combined weight of slug & wad is 375 grains or 24 grams - same weight as the 1500 fps target loads we use over here.



I hope the new profile and increased speed will create a true drag on the rear of the slug and keep it pointed nose forward.
The old subsonic design would start wobbling profusely after fifty to sixty yards - perhaps caused by the pressure wave building up in front of the slug.

Now it only remains to work up a chronographed load and test for accuracy and stability.

This is confusing to me. Brenneke Classic 12 ga. slugs are 1-1/8 oz. (490 gr.), muzzle velocity of 1500 fps and fly accurately to 100 yards or more even though they become sub-sonic somewhere between 50 and 75 yards, according to factory data. This slug/tailwad is a close approximation of Brenneke's design, albeit with some differences; Wouldn't it make sense to increase the slug weight and load to higher pressure? 1500 fps should be attainable even to us handloaders, yes? Or, no?

[Cap'n Morgan]

Centershot

While 1500 fps is certainly possible with a 1-1/8 ounce slug, I'm too much of a chicken to go down that road. The new design may look a bit like an original Brenneke, but it's only the helical ribs that remains from that design. As long as the slug is not properly stabilized those ribs will not work as intended and the whole project will be somewhat moot. But until the slug is tested and fails I'm suffering from incurable optimism

[Cap'n Morgan]

At long last I got around to re-test my latest slug design.

As you may - or probably may not - remember, I had high hope in this finned wad/solid slug combo. Unfortunately, the design proved to be quite unstable, with almost every single shot hitting the target sideways instead on nose-on. Hogtamer mentioned, that since a slow subsonic speed didn't work, maybe more speed would improve things. I had nothing to lose and made a new, lighter slug - upped the speed to 1450 fps and gave it a shot, so to speak...

The range was 50 meters. I fired five rounds, one on them either missed the target or went through a previous hole. The four holes measure a little over 4", and all four slugs has hit the target sideways! Clearly, although the slug has the center of gravity well forward, the overall length is too short to stabilize it flight.

I'm throwing in the towel here. Next design (and last, I promise) will be a swaged Brenneke slug of proven design.


The pictures speak for themselves:



Notice how nicely the slugs fit the holes

[bikerbeans]

Capt.,

That lower hole looks like two impacts to me. Maybe one of your slugs hit nose on? Good luck with the Brenneke clone.

BB

[W.R.Buchanan]

Capt: I went back and read this entire tread. I see some issues that might help.

What you are trying to do is essentially an "AQ/Brenneke style slug." I just happened to have a new one on my desk in front of me so I took some pics.

The center of gravity on the AQ slug is WAAAAY forward. The entire slug is 1 1/8" long and the CG is less than 1/4" from the Front! It is approximately at the juncture of the nose radius and strait portion of the slug. The tail wad, or more properly fins are flared to insure bite and the tail plugs into the slug the exact opposite of what you did. That slug is so weight forward that with the slightest nudge it will roll right up on it's nose and stay there.

I just happen to have a Brenneke slug on my desk as well. I unscrewed the wad and the base is hollow except for the post that is threaded so the screw can hold the wad onto the slug.This is similar to Longbow's modified Lee Slugs,,, once again CG well forward.

The other type of Brenneke slug has a plastic wad that is plugged into the hollow base of the slug and is shoved into that base farther as it collapses at the moment of firing.

Even my Lee Slugs will roll up onto their nose with little assistance. The Russian Slugs are similar in that they also have hollow bases.

The Lightfield slug is supposed to be the most accurate shotgun slug there is. Hollow Base, weight way forward.

All these slugs have one thing in common. They all have deep hollow bases and their CG's are all at 1/4 to 1/3 of the total length, off the nose.

My STI Slugs with the brass inserts are 1 7/8" long and balance at slightly less than 1/2" off the nose. (They are for rifled barrels but the same holds true for them.)

I think the problem you have is that your CG is not far enough forward.

I think if you reverse the design so that the wad plugs into the nose, as opposed to the nose plugging into the wad, you'd have it beat.

On another note,,, Your mould work is excellent!

Randy

[longbow]

turbo1889 had some balance point guidelines and length to diameter relationships he claimed were correct and that a slug over 1 1/2 or maybe 2 times diameter would be unstable. Now, I think he was talking Foster lead slugs not attached wad slugs but that always stuck with me and is the reason I have questioned form versus CG. The AQ is certainly long and very nose heavy but apparently like a rifled slug there is some spin imparted by the spiral vanes so maybe that plays a part. turbo maintained that the Lyman sabot slug was unstable at transonic velocity and would start to tumble (from smoothbore)... yet, I see Taofledermaus video of the Moose .69 Minie and Lyman 730 gr. .69 Minie flying perfectly stable from smoothbore. Both have pointy noses where the weight is and large bodies where the weight isn't. I'd think if they tipped there is noticeably more drag on the tail than the nose.

So, point being that maybe a somewhat more streamlined/pointy slug might be better?

Of course I am guessing and somewhat grasping at straws having tried many things but mostly being marginally successful of failing. My Moose Minie copy yet to be tested (after the archery shoot!).

Maybe a Moose Minie copy with attached wad would be something to try?

Longbow

[Cap'n Morgan]

Randy, one of the reasons I chose the "hollow wad" design instead of "hollow slug" was to have a slug that was easy to cast without a core pin in the mold. Also, the "stem" on the slug should support the wad against compression during launch. I may take another look at the wad injection mold to see if it can be modified without too much work involved.

LB, I have contemplated a more streamlined/pointed design myself. But apparently a hemisphere is the best ballistic profile as long as the speed is in the subsonic area. Federal's Foster slug is still supersonic out to 100 yards, but they start out at a brisk 1520 fps with a 1-1/8 ounce load and I'm a little reluctant to go the highspeed way (besides, I'm running low on Blue Dot with little chance to find more)

[W.R.Buchanan]

I used to think that a drag stabilized slug would be accurate. Then my mind drifted back to my Airplane Mechanicing days.

I remembered that tail surfaces on certain planes, got "blanketed" by the Airflow deflected off the leading edge of the wing causing them to be ineffective. In effect, the wing would block the airflow over the tail surfaces so they wouldn't do anything. In the case of the Bell X1 that Yeager flew, the leading edge of the stabilizer deflected/blanketed the airflow over the elevator, rendering it useless. The fix for that was to tilt the whole stabilizer. In the case of the F4 which was a evolution of the F101 the Tail Surfaces were angled down so they couldn't be blanketed by the wing. No matter what attitude the plane was in some part of the elevator was in the air stream.

With Slugs none of them are all that aerodynamic to begin with. As a result the airflow off the nose is well outside of the tail wad and thus the slug relies on it's weight forward to keep it going in the assigned direction. If the slug tilts enough in flight the airflow can contact the off side and push it back the other way. However it won't tilt it back to the center line it will simply tilt it back the other way until it hits the other side of the airflow. In other words the slug will oscillate back and forth as it travels down range. If the tail wad was truly "In the Wind" the tail would keep the slug flying strait by virtue of drag. Since the airflow is well outside of the tail, it can't happen, and thus the slug relies on it's weight being well forward to keep it on track.

I don't see how a Lyman Sabot slug can fly strait unless it is released from the wad perfectly true to the line of travel. If it is spun, sure. It is weight forward but not nearly as much as Lee slugs or others. The Foster Style slugs have far superior Aerodynamics and the accuracy I've seen from them out to 50 yards is fine from a smoothbore. I got one group that is 1 x 1.5 form the A5 which is not half bad.

Same with round balls which seem to have alot more potential than we give them credit for. If you can get a ball with no Sprue sticking out, it should go down whatever path it was directed on and only be affected by gravity. Seemed to have worked fine for 250-300 years and if they would have figured out that the guns needed decent sights earlier they probably would have lasted longer.

This is an interesting subject and I think we are approaching a more comprehensive understanding every day. I have not seen any definitive source on this subject and if anyone has any published information on Slug Aerodynamics a link to it could be helpful.

Randy

[longbow]

Randy:

I am with you on the oscillation thing. I have felt for some time that a "too long" and "too light tail wad" will result in oscillation. As I mentioned, turbo1889 had some comments about length to diameter ratios and what works best but I believe that was more for all lead Foster style slugs.

The blanketing issue I am sure I have run into as I am sure we all have but in particular when I made my 6 finned slug mould I thought it would work as well or better than a Foster style... Wrong! They did fly nose first but accuracy was quite random where similar length and weight Foster style slugs shot not badly. I believe the "blanketing" kept the air away from the vanes where the solid Cylindrical skirt of the Foster has more surface area to pick up whatever air/drag it can.

I am still thinking that hemispherical or pointy type noses are better than big meplats too but until I test my Moose Minie copies I am, as usual, guessing. Look where that's got me!

Archery is still keeping me from shotgun slugs and will for another week or so, but I'll be back!

Longbow

[W.R.Buchanan]

The area behind the nose of the slug is actually in a vacuum, as the slug moves forward it displaces the air outward from the nose and there is nothing to replace it until the slug is farther down range. Thus the area directly behind the slug is evacuated as the slug travels forward and ambient air pressure is insufficient to close the gap behind it until the slug slows enough to reduce the deflection of the airflow until it hugs the slug more tightly. It never really touches the slug as there is always a laminar layer of non moving air around the slug. Because of this Laminar Layer the slug is actually larger in the air than it actually is.

Same holds true on boats with shiny hulls, the Laminar Layer around the hull is larger than one around the same hull with a rougher finish. Harley Davidson actually figured this out with respect to polished intake ports which were essentially smaller than the same port with a sand blasted finish. Thus allowing a larger volume of air to pass thru the rougher finished port. It was immediately picked up by the Americas Cup Engineers and our crews got busy sanding the bottoms for a flat finish. In the 1968 Races our boat picked almost 1 full knot of speed off wind which in 12 Meter Mono Hull Racing is alot!

This is now Basic Fluid Dynamics.

Randy