The Relationship of Center of Gravity and Pressure with Slugs?

[Ranch Dog]

This is from another thread on another topic...

Now I am wondering... shouldn't center of pressure be behind the CG for drag stabilized slugs and in front for slugs from rifled guns?

From what I've seen of seen of the slow-motion videos, that hasn't been working out very well for the Lee slugs as their center of pressure is definately behind the center of gravity. I think for any projectile to be successful down range, a repeatable MOA of any size, the center of gravity needs to be slightly aft of center as well of the center of pressure. From that, the center of pressure needs to be slightly ahead of the center of gravity.

The problem for most is measuring either value. The math is tough and the only user-friendly software that can do the math, as far as I know, is TMT's Cast Bullet Design (http://tmtpages.com/). Even that program has problems with a tapered skirt with a hollow base. Same with the actual "key" within the hollow base of the Lee. Still, I think the calculated measurement is very close. The TMT software measures the values from the base of the projectile expressed in a percent of the total bullet length. As a general rule, I like seeing a CG about 47.0 to 48.5% from base, with the CP greater, and within 1% of the calculated CG. This is simply a comparison on my part, the numbers from the drawing against MOA performance downrange.


Have you considered round balls? 0.678" RB's in an appropriate shotcup are a good fit. 0.662" RB's in steel shot shotcups are a good fit. and 0.735" RB's are a good fit for bore size. Even 0.690" RB's in thin petal shot cups could work.
I haven't to date as the rules for the hunt specifically state "slugs." I'm not a fan of round balls for hunting, I've shot a bunch of small game with my centerfires, 218 Bee through 38-55 Win, using alloys from pure lead to Lyman #2, and never have I cleanly dispatched game, not once. I am going to pursue round balls through my shotgun shooting this year, just to see how they perform in smooth vs. rifled barrels.

Theoretically, the CG and CP are centered in the round ball. I've always heard to put the sprue cut up front, but what makes sense to me it to put it to the back. That flat represents missing material which would shift the CG slightly aft, leaving the CP at 50%.

Of course, all this is just armchairing. I'm one that likes burning powder even if it doesn't go as planned.:veryconfu

[megasupermagnum]

You've never dispatched small game cleanly? I've cleanly killed small game with .177 bb guns and blowguns, although the blowgun dart had a broadhead.

The problem with putting the sprue down, is that you can't see it to align. You could eyeball it, and put a sharpie dot on the other side, I choose the easy route and put sprue up. As slug shooters, we have a lot more to deal with than just bullet fit and balance. Slugs that shoot good at 75 yards are often wild fliers by 150. Slugs that have the balance to fly to 200 yards, often don't shoot good.

[Ranch Dog]

You've never dispatched small game cleanly?
Only with head shots.

[Mr_Sheesh]

CP has to be behind CG or your bullet is dynamically unstable. Same thing applies for aircraft and rockets (model or full size); Look at a rocket and you see larger fins on the back of them, to bring CP backwards.

Think of it as "the drag pulls back on the bullet from the CP, and the inertia pushes forwards from the CG" and you can see why. If the CG were behind it'd happily swap ends with the CP, which would mess your accuracy up horribly.

Model Rocketry handbooks or "learn to be a pilot" handbooks should cover this pretty well as it's one of the fundamentals of either field.

[longbow]

Ranch Dog:

There are round balls and there are round balls! A 12 ga. round ball is a substantial projectile. A WW 0.735" RB weighs about 575 grs. and is of course LARGE!

Not sure if "slug" is defined as a standard Foster HB, solid slug, Brenneke or whether it just refers to a single "bore" diameter projectile from a shotgun but I doubt many living things would walk away after being shot with a hard cast 12 ga. ball at 1400/1500 FPS!

Longbow

[megasupermagnum]

Ranch Dog:

There are round balls and there are round balls! A 12 ga. round ball is a substantial projectile. A WW 0.735" RB weighs about 575 grs. and is of course LARGE!

Not sure if "slug" is defined as a standard Foster HB, solid slug, Brenneke or whether it just refers to a single "bore" diameter projectile from a shotgun but I doubt many living things would walk away after being shot with a hard cast 12 ga. ball at 1400/1500 FPS!

Longbow

I showed some guys the .735" round ball. They thought they were small cannon balls! You could cause damage to someone just throwing them by hand.

One thing I forgot to bring up, they don't come out of the end of the gun round. They end up oval shaped, with a 3/16"-1/4" band that's engraved by rifling. I wouldn't worry which end the sprue is on at that point. Also, I've found my best luck with a scoop of PSB buffer under the balls. Recovered slugs show a cool pattern on the buffer side. Groups are astounding at 50 yards, but I'm still trying to find that 100+ yard load. So far I average in the 6" range at 100 yards and the round ball. If I could figure out why one side engraves more than the other, and solve it, I bet groups would improve dramatically.

[W.R.Buchanan]

Guys, Sheesh has it right. Also after dropping some of my slugs many times they always hit nose first meaning the CG is definitely forward.

Also LB's point about walking away from a Round Ball hit is spot on, and you can consult with the British Empire for the results of that, as the Brown Bess Musket was standard issue for over 100 years (1722 -1836) and more. Getting hit by a .75 cal round ball would definitely ruin your day.This gun was made obsolete by the Percussion Cap and then further by the self contained cartridge.

BUT!!! A 12 ga. Shotgun is essentially a Breech Loading Repeating Musket using self contained rounds. (the term "Rounds" came from Round Balls.) Many things are different but the payload can easily be the same as 300 years ago and it is just as effective today as then. It's just easier to clean up after. It lives on due to the variety of stuff you can shoot out of it.

If you go one farther and look at these Lyman Slugs you see basically a Wad Cutter and as such the energy transfer of the slug on the target is instantaneous. I don't see super penetration, but I do see knockdown power.

More numbers. I did some ftlb Calcs today versus TKO numbers.

Lyman Slug at 1300 fps 1877 ftlb or just under a .243 but the TKO is 67. TKO of the .243 is 11

A 405 gr .45-70 at 1600 fps is only TKO 42 but 2300 ftlb.

Lyman Slug at 1500 fps, 2500 ftlb with TKO of 78 where as a .458/500 Win Mag is 5100 ftlb but a TKO of only 70.

Federal 1 1/8 oz slugs at 1610 fps are 2875 ftlb with a TKO of 83 .30-06/180 is 2800 ftlb but TKO is only 21

What the TKO is showing is the relative energy transfer of the projectile to the target. Where as the FT LB is showing the available energy.

Used to be that the method of figuring ft lbs was to shoot a hanging steel plate and see how far it moved. This method extracted all the energy of the bullet on impact. But I wonder if the results would be more like the TKO numbers as opposed to ftlb numbers?

The difference is that the smaller dia projectile doesn't transfer it's energy to the soft target as efficiently as the larger diameter slug does. So it becomes the old Porsche doing 150 mph versus the Bus doing 90 comparison. The bus has a larger frontal area, therefore it will transfer more of it's energy to you faster than the Porsche will. Both will kill you but one will squash you flat in the process.

That is "knock down power." Something to think about.

Randy

[longbow]

MSM:

I've found the same thing in my smoothbore. Generally the 0.735" RB's show an uneven "belt" around the middle. I have thought it was due to one or two things... or maybe some of both:

- the ball leaving the hull a bit off center then smacking the forcing cone so rolling into the bore
- the ball picking up a spin as it opens the crimp so it is rotating when it hits the bore... skidding to a stop (same net effect as above)

I strongly suspect that if a hull fit full length into a chamber when fired and there was a more abrupt leade like in a rifle we would not see the uneven "belt". The ball would be driven past the crimp and directly into the bore/rifling with little to no chance of picking up spin.

However, I digress again... this thread is about CG and CP.

My limited understanding of this is that with rifle and handgun boolits (or bullets) the CP should be forward of the CG for stability (think jacketed HP target bullets) where I am pretty sure for a drag stabilized slug the CP should be aft of the CG.

I am not actually sure how the physics works with a round ball. One would initially think that the CG and CP would both be at the center of the RB but... once there is a shockwave in front and drag behind is that true?

Does the CP shift due to the shockwave? If so I'd suspect it shifts forward and maybe that is why RB's pick up a spin at longer distance... or at least I suspect they pick up a spin explaining their curve ball trajectories at longer ranges.

Is CP due to geometry or is it a dynamic thing that is affected by air pressure/shockwave?

Some smart guy out there must know these things. I am a simple country bumpkin so without doing a bunch of research I don't have an answer.

To add to the confusion turbo1889 posted that the Lyman sabot slug was not stable out of smoothbore after it went transonic, that it would tumble. Yet I have read posts where people claim very good accuracy out to 100 yards from smoothbore. I'd be surprised it they were still supersonic at 100 yards.

Now we have at least two people I will believe if they post their results using the new NOE Lyman clone. Not sure if Ranch Dog has a smoothbore to test them in but Randy certainly does.

I would like to buy one of the NOE moulds and probably should but not only will it cost me about $200 CDN by the time I have it, turbo convinced me several years ago that slugs cast from my home made moulds will shoot as well. I passed on the Mihec Lyman clone that time. Maybe yes, maybe no but I'm off work again so will leave a mould purchase until another time if they prove to be good shooters by people I trust.

For anyone with a Lyman sabot slug mould or clone, lease post results from both rifled and smoothbore guns.

Longbow

[Ranch Dog]

CP has to be behind CG or your bullet is dynamically unstable. Same thing applies for aircraft and rockets (model or full size); Look at a rocket and you see larger fins on the back of them, to bring CP backwards.

Think of it as "the drag pulls back on the bullet from the CP, and the inertia pushes forwards from the CG" and you can see why. If the CG were behind it'd happily swap ends with the CP, which would mess your accuracy up horribly.

Model Rocketry handbooks or "learn to be a pilot" handbooks should cover this pretty well as it's one of the fundamentals of either field.
I agree with you on aircraft and rockets from my experience as a 31-year airline pilot. Aircraft have wings and rockets have propulsion. Bullets are different, the center of pressure is always ahead of the center of gravity as all they have is the effects of external ballistics causing the pressure against their shape. It's the same with an artillery projectile. I do have several hundred factory bullet drawings that confirm the positions of the two references plus about twice as many cast bullet drawings, bullets that shoot great. The hollow base bullets designs I've worked with still have the CP ahead of the GG. The only place I've seen the reference positions reversed is with the hollow base slugs and the pellets used in airguns.

From Long Range Shooting: External Ballistics - Bullet Shape (https://loadoutroom.com/thearmsguide/long-range-shooting-external-ballistics-bullet-shape/), here is the short of it.

"Therefore, because of the bullet shape, the projectile will always fly at an angle, called angle of attack, relative to the trajectory. ... Since the point of pressure is positioned in front of the center of mass, the air flow will force the bullet to rotate backward, pivoting on its center of mass."

https://loadoutroom.com/wp-content/uploads/2017/06/Featured-static-stab.jpg


Ranch Dog:

There are round balls and there are round balls! A 12 ga. round ball is a substantial projectile. A WW 0.735" RB weighs about 575 grs. and is of course LARGE!

Not sure if "slug" is defined as a standard Foster HB, solid slug, Brenneke or whether it just refers to a single "bore" diameter projectile from a shotgun but I doubt many living things would walk away after being shot with a hard cast 12 ga. ball at 1400/1500 FPS!
Very true longbow, a 12 gauge slug is not your thirty-something caliber roundball. Like I said, I'm going to try them to see how they shoot and will eventually send one towards a hog, that easy here in South Texas.

As far as the Refuge hunt goes, I'm not going to battle the feds over whether a round ball is a slug or vs. versa. I'm really in a fix over the hunt anyway. I'm supposed to leave Thursday morning, but my 90-year-old dad is having some issues. He lives here on my ranch in a separate house. Unfortunately, my wife left yesterday to go to PA to visit her sister who is having health issues. I would hate to miss the hunt after all this prep, but of course, my dad would come first.

[longbow]

Sorry to hear about your dad and sister in law. Tough times when family is ailing. Bad timing but family comes first for sure.

I hope all works out for the best and health issues are taken care of.

Take care.

Longbow

[W.R.Buchanan]

I must have a misunderstanding of Center of Pressure as to my mind the CP is at the rear end of the bullet or where the push is coming from. How is Center of Pressure established?

Also the description of angle of attack seems incorrect as a Bullet's Axis of Rotation does in fact follow the trajectory as long as the amount of spin is adequate to keep it stabilized in flight. When that spin is no longer adequate to stabilize the bullet it starts to Yaw and that Yaw will be around the Center of Gravity of the bullet with the front end spiraling around the Axis of whatever rotation is left. In other words the bullet will keyhole. But with multiple shots on the same target the keyholes won't all be going the same way so that point of spin degradation will be random. Eventually if shot out past the point where the spin is no longer affecting the flight the bullet will fall strait down sideways as the air pressure equalizes around the the length of the bullet. Like if you shot it off the rim of the Grand Canyon, the bullet wouldn't reach the other side and simply fall to the bottom and should hit the ground sideways. If you drop a rifle bullet, it will fall flat.

Our Lyman Slugs however will hit nose first. If dropped sideways from as low as 3-4 feet, they have enough weight forward to still hit nose first. I did it a bunch of times today and it hit nose first every time.

Am I FOS here?

Randy

[pashiner]

I believe that the illustration in ranch dog's post depicts an over-stabilized bullet with it's nose-up attitude in reference to the trajectory. When this happens, the gyroscopic forces from excessive spin broaden the angle of attack. I wonder what that does to B.C. , and if it effectively moves the center of pressure?

[Tom Myers]

I must have a misunderstanding of Center of Pressure as to my mind the CP is at the rear end of the bullet or where the push is coming from. How is Center of Pressure established?
Randy

Randy,
To put it simply,

Center of Gravity is the balance point of an actual bullet. Gravity, inertia and rotational forces act upon the center of mass of the bullet.
Center of pressure is the balance point of a bullet profile. Air pressure acts upon the geographical center of the profile of the bullet.

The Center of Gravity is calculated by averaging the distance from the base of the bullet to the center of gravity of each segment of the bullet.
The Center of Pressure is calculated by averaging the distance from the base of the bullet to the geographical center of a profile of each segment of the bullet.

You can find the approximate Center of Gravity by balancing the actual bullet on a knife edge.
You can find the approximate Center of Pressure by balancing a scale cardboard cutout of the bullet on a knife edge.

The pressure is created upon the lower side of the bullet profile by air pressure as the bullet travels the length of the trajectory with a slightly nose up attitude.

Hope this helps.

[Ranch Dog]

Our Lyman Slugs however will hit nose first. If dropped sideways from as low as 3-4 feet, they have enough weight forward to hit nose still first. I did it a bunch of times today, and it hit nose first every time.
That is a perfect explanation of why they don't shoot well, the CG is too far forward (greater than 50% from base). I just held a .460" 525-grain bullet horizontally and dropped it from the same distance, and it hits the ground horizontal. I dropped it from 10', it still hits horizontal. CP isn't involved with a dead drop.

There is no magic why outfits like Lightfield produce slugs that perform like rifle bullets; they are slugs and not saboted rifle bullets, they've paid attention to the principles behind interior and exterior ballistics. If your need is short range, then you have what you need in a hollow base design like the Lee. I purposely have not included the Lyman with the Lee, as I have not shot it.

pashiner, the illustration is just that. The reference points, trajectory, and angles are exaggerated for example. The tolerances of all this are rather tight in reality. I've designed about 50 bullets that are in use and have had a couple fail because I push a bit on the CG and CP positioning and their relationship to each other. This stuff is tight and has to be respected; positioning runs a range of about 3.5% of total bullet length and the correlation to each other about 1.75% of overall bullet length. Even the weight and arm of a gas check is considered. Hollow base slugs are grossly outside these limits.

Thanks for your comments Longbow, our good Lord lent his response to my dilemma as to go or stay. At 5:00 this morning, the power went out and was out for two hours. Not too big a deal, but it could have been. It was 26°, not a big deal for most, but a rarity in South Texas especially for this time of year. Our houses aren't built to deal with it. I have a backup generator, but there is a bit to getting the three homes off line and dedicating one to service. The setup is also more for a hurricanes and the hot weather around those events. I cannot run my central heat on it. I'm not sure he could do everything out in the cold on his own. The reality, Dad always trumps a nilgai. I'm getting ready to grill some pancakes for us, he did not even know the electric was out.

[Ranch Dog]

Hey Tom! Thanks for the explanations!

[Mr_Sheesh]

In model rocketry the usual way to determine CP is to cut a silhouette of the rocket out of cardboard and balance it front/back wise, the CP is where that silhouette balances, on the centerline of the rocket. As https://spaceflightsystems.grc.nasa.gov/education/rocket/rktcp.html

And to determine CG you just balance the actual rocket using a string (with everything installed so engine loaded, parachute/streamer in place, etc.)

Agreed that ballistics at trans sonic speeds will change external pressure and drag but I'm not an aerodynamicist. Once the bullet falls below the speed of sound, we're back to the CG and CP needing to be in the right relationship though...

[Ranch Dog]

I need to add that Mr. Tom Myers has taught me more about bullets and ballistics, in conversation and through his software, than any other source. Might be best said this way; thank goodness Lee Precision had cheap custom molds before I met him, some missed the mark because I wasn't paying attention to the details that he has taught me.

[megasupermagnum]

The problem with lightfield slugs, and other tail wad slugs is the terrible BC. They shoot about as flat as a round ball, maybe worse. I used to like the LBC sabot slug from BPI, it was a slug of a similar design to lightfield. I could launch them at 1950 fps, and they shot pretty good. The problem is that tail wad caused them to drop about 30"-36" at 200 yards with a 100 yard zero.

[Blood Trail]

In regards to 1oz Lee slugs, i believe why pose a fit to reload accurately is because it's a balanced projectile with the key design. I've been wanting to mod one of my lee molds to completely remove the key drive and make it a true hollow base. That way, it will make more nose heavy for stability.

[popper]

I know, this is posted about SG slugs. Velocity is a vector quantity. Break into vertical and horiz and it is almost never along the bullet centerline. Rising and falling bullets have the center of pressure changing due to 'slight' variations of vertical fps. Farther distance between CG & CP creates more torque to swap ends. That is why we spin bullets, gyro momentum is (usually) much greater than CG/CP torque. Rockets ( & VLDs) have a high BC/SD and don't need as much spin. The 'transonic' region differs between bullets and rockets. It really is the region where rotational momentum and forward momentum meet and allow CG/CP to take effect. Basically stating that rocket/plane dynamics and bullets differ. I won't even try tackling the SS shock wave variations.
Michael, hope the hunt and old folks stuff works out for your family.

[W.R.Buchanan]

Randy,
To put it simply,

Center of Gravity is the balance point of an actual bullet. Gravity, inertia and rotational forces act upon the center of mass of the bullet.
Center of pressure is the balance point of a bullet profile. Air pressure acts upon the geographical center of the profile of the bullet.

The Center of Gravity is calculated by averaging the distance from the base of the bullet to the center of gravity of each segment of the bullet.
The Center of Pressure is calculated by averaging the distance from the base of the bullet to the geographical center of a profile of each segment of the bullet.

You can find the approximate Center of Gravity by balancing the actual bullet on a knife edge.
You can find the approximate Center of Pressure by balancing a scale cardboard cutout of the bullet on a knife edge.

The pressure is created upon the lower side of the bullet profile by air pressure as the bullet travels the length of the trajectory with a slightly nose up attitude.

Hope this helps.

Thanks for the explanation. Still don't fully comprehend the CP. Is that a computer generated value?

The relationship between the CG and CP? What is optimal? Or is there an optimal? And does this change with the type of bullet profile? IE: long and skinny vs. short and fat.

The actual design of the Lyman Slug closely follows the average Diabolo Airgun Pellet and that design has been proven to be very accurate in Airguns within a certain range (10M). I have several that will essentially put all their shots thru the same hole for as long as you can stand to do it. The greatest accuracy seems to be delivered at a velocity of around 600 fps.

I wonder if there is a velocity "Sweet Spot" for these larger pellets as well? And that maybe we are pushing that envelope and trading Accuracy for Horsepower?

From a smooth bore It seems that the Lyman slug will only produce whatever accuracy is granted by divine guidance. However from a rifled barrel I would expect it to act like an Airgun Pellet. Lets face it the slug has the Aerodynamics of a Refrigerator, but that doesn't mean that it can't provide a useful service within the ranges it is designed to be used at. It is just NOT going to be one hole accuracy. Too many variables to unravel. So you take what you can get.

This all comes under the heading of the statement I have made here and elsewhere so many times regarding Accuracy of different weapons.
Mini14's come to mind as I have fought that battle many times. There is "wished for accuracy," and there is Reality. Only one is useful.

Many people regard the Mini 14's accuracy as completely unusable. And in fact think that every gun must exhibit sub MOA accuracy in order to be useful.

We all know that this is a stupid way to look at it. My Mini 14 is a solid 1.5" gun and It will kill you just as dead as a 3/4" gun or for that matter a 3" gun. By extension these shotguns are only going to be 100 to maybe 125 yard guns and if we can get one inside 3" at 100 yards I would say we had reached true nirvana. But twice that would probably do the job as the size of the projectile makes up for it's inability to hit in the same place every time.

It all gets down to the end result that you work up a load and then you go shoot something with it.

If you end up eating what you shot, then I would say you were successful.

Randy

[Ranch Dog]

Thanks for the technical stuff popper and thanks for your kind words. After the power was up, I made my dada good ranch breakfast!

https://www.ranchdogoutdoors.com/family/dad/20181114.jpg

I told him I'd rather hit the road with him, a couple of day trips around South Texas than go on the hunt, so that is what we are getting ready to do. We are going to visit some country we haven't seen in a while, just out and back as he likes being home at night.

[Ranch Dog]

The problem with lightfield slugs, and other tail wad slugs is the terrible BC. They shoot about as flat as a round ball, maybe worse. I used to like the LBC sabot slug from BPI, it was a slug of a similar design to lightfield. I could launch them at 1950 fps, and they shot pretty good. The problem is that tail wad caused them to drop about 30"-36" at 200 yards with a 100 yard zero.

As long as they are predictable, I don't have a problem with the drop. Not much difference that a 45-70 Govt with a heavy bullet, you got to have a dependable MOA though.

Just finished the shooting for the 680-500-HB. Great at 50-yards, better than then Lee. Still, MOY (Minute of Yardstick) at 100-yards.

For grins, I had pulled the LightField components and shot the total projectile with the same load (25.6-grains of International, image says 25). I shot them immediately after the 680-500-HB with the same POA. Two in the same hole.

https://www.ranchdogoutdoors.com/Firearms/512/images/lightfield_05.jpg

https://www.ranchdogoutdoors.com/Firearms/512/reloading/images/LF_reload_01.jpg

https://www.ranchdogoutdoors.com/Firearms/512/reloading/images/LF_reload_02.jpg

https://www.ranchdogoutdoors.com/Firearms/512/images/lightfield_07.jpg

When that was done, tried the 2 3/4" Lightfield from the used cylinder bore, rifle sighted barrel I just bought. I didn't clean the barrel, didn't fiddle with the sights, didn't do anything. Just put the barrel on and shot it at 50-yards. All three shots touched.

https://www.ranchdogoutdoors.com/Firearms/NH600/images/lightfield_hybred_elite_01.jpg

The only thing I don't like about the Lightfields is that those three hulls represent seven dollars and fifty cents. Of course, that is a drop in the bucket compared what I've spent trying to get a home cast slug out to 100-yards with a huntable MOA.

I got to go, but when I come back, I'm going to drop these old designs and do something different.

[popper]

Yea, have fun and keep them happy. That breakfast would put a smile on my face. Mom's 99 and not in very good shape, in a mental care now, really sad to go visit. Enjoy while you can.

[megasupermagnum]

I hope I still look that good at 90.

Sure the drop is consistent, gravity doesn't change. I just plugged my personal results into the Hornady ballistic calculator. It looks like a BC of about .06. With just a 10mph wind, calculated drift at 200 yards is 65"! Maybe Lightfield slugs are a little better than the LBC, but that tail wad is a killer. No matter how you cut it, I just can't come up with a slug that's good for more than 125 yards. I've recently been turned on to a factory load, the Federal "sabot slug". It is a swaged 1 ounce hollow point. So far results are fantastic, sub 2 MOA at 100 yards. They sell for $7 a box too. I'm going to be trying these at longer range this winter.

[W.R.Buchanan]

After seeing what a Lightfield Slug actually looks like I can see why they shoot so good. They are drag stabilized, which is something we haven't talked about much.

It is also a Wasp Waisted design, but the kicker is the attached wad which uses the hose barb type of attachment like the various Russian slugs we saw a few months ago.

I personally think the attached wad is the way to go for accuracy. And I can see it working for both smooth bore and rifled barrels.

On another more recent note ; I'd like to see how the CG/CP relationship is on those slugs and compare it to our Lyman Clones.

Randy

.

[popper]

CP is a drag induced number. Frictional drag, depends on fps, is virtually equal on all Diam's of the slug so has little influence on stability, just slows it down. Lite field slugs have the tail in airflow that puts the CP way behind the CG and adds stability. Shuttlecock theory.

[megasupermagnum]

I just looked at the pictures. Lightfield uses Bluedot powder. Whodathunck it. What was the charge weight of the factory Lightfield load?

[longbow]

Ranch Dog:

If you are thinking of something new and different for slugs you will likely be better served by a full bore slug.

I'm no wizard here and am still struggling with slugs in smoothbores so take this with a grain of salt...

Greg Sappington was working on wad slugs quite a number of years ago and he asked me to make him a mould to cast a slug he designed so it would fit a steel shot wad as a discarding sabot. It worked but he made some changes so i made him another mould. Same basic design and still to fit into a steel shot wad (maybe CSD wad?). While both slugs worked and terminal performance was what he wanted, accuracy was not as good as he wanted and that mostly, if not all, due to the inconsistencies in the shotcups. They just aren't made to sabot standards and tolerances. In the end he rethought things and went to a machined Delrin sabot and sub bore slug.

Alternately getting rid of the shotcup or sabot and going to full bore slug will accomplish the same thing by removing the inaccurate component... the shot cup.

Since I like to do things myself with what is readily available and little if any specialized equipment of components, I would go full bore slug. Accurate moulds has quite a collection of full bore designs now so good selection. However, the slugs I like are the old Dixie Tusker and the Paradox bullets.

The Dixie Tusker was a very nice slug in my opinion. It was 600 grs. and hollow base though it was intended for rifled gun. James Gates posted the drawing here for others to use which was very generous of him. I think James used the hollow base to provide more bearing length without raising weight too much. A very nice design to my eyes.

The Paradox bullets always fascinated me so I'd get a mould made just because I like them. They are a bit heavy at about 740 grs. so load data is a bit sparse but I like them.

Another option is the Hammerhead slugs. You have to buy the special wads but you can buy a mould and cast your own slugs. I like that. Also, Blood trail says they are very accurate so that is a good endorsement for those slugs.

Just some food for thought for a guy who wants to try something different.

Longbow

[OnHoPr]

Good evening gentlemen. I think you are kinda putting the cart before the horse on the projectile technology thesis. Especially with wad style slugs. The better ones are the Buckhammer style slugs because their sabot style sides have greater thickness in the material used and can handle the jump and travel from hull to end of barrel. Though, I still believe that the wad cushion prevents them from becoming more accurate. I think the wad base will always have burdens too. Should it drop or should it stay attached. How concentric can you make it in alignment with the slug. How can it endure ignition and down the barrel. The seemingly easiest is the shot cup slug, but it seems to be the most difficult to keep consistent not only with the cushion, but the petals as well. The ones I seen that seem to have hopeful expectations were with steel wad cups with no cushion. But, trying to get those concentric on wall thickness created a problem as well as the diameter of the slug with overall diameter and shoving in a hull.

All of these slugs have like sheeeit for BC. You have to have less than 3 mph winds just to see if you can get in the 2 MOA range. Maybe they designed the slugs to large for the thin clays & field load shot cups and need something in the .630 to .650 range for the steel cups for durability. If you go full bore with the heavies you get some heavy duty recoil. I guess they make a few lighter full bores, but then you have to have your forcing cone, lead, throat, whatever designed well enough to not damage the slug from ignition. Something like the Hastings Laser slug sabot, like the Buckhammer and Lightfield, but just the sabot and cast the slug while working with your own wad column.

Edit addition, Slugsrus sabots.

I mean to suggest, have we come very far at all in the last 60 + years when it comes to shootin the slug venues. I am not talking about rifled barrels and saboted bullets. Take a 60s' Deerslayer, put a 4X Weaver on it with one of the three major manufacturer foster slugs on a calm winds day and it will shoot 4 MOA off the bench ALL DAY LONG.lol You would think adding rifling to a barrel the MOA would shrink wouldn't you. Heck, I just may be thinking a little to critically from the general 50-60 slug gun to the consistent 100 yd slug gun and the 75-80 slug gun is a step in between while the 125 yarder is something dreamed about. Something like shootin the 300 savage to 200 yds pretty easily to the next steps of 350 yds and then to 500 yds might have some difficulties.

Lot of criteria to think about though. From individual guns and their barrels to all the components and reloading practices.

Oh, and Ranch Dog, how are you suppose to shoot good when you have troubles keeping your pancakes round. :kidding::bigsmyl2:

[Mr_Sheesh]

Putting a wad or other light object behind your slug will keep the CP at "midpoint" of the slug; The wad being light, the CG will indeed be WAY forwards of the CP. That's why attached light wads stabilize slugs well :)

If you put another lead slug behind the slug, it wouldn't stabilize the slug. (And would increase pressure if you didn't reduce the powder charge etc.) That'd move the CP back, but also the CG.

I have to admit that I've wondered how they calculate CP for a "grid fin" like the MOABs use; It would have a lot more effective rearward movement of the CP than the cardboard outline method would indicate. But I am not planning on making a firearm to launch a MOAB any time soon, I'll leave that to the USAF :)

[Cap'n Morgan]

It is hard - maybe even impossible - to design a full-bore 12 gauge pure lead slug with the Center of Gravity sufficiently forward to stabilize the slug from a smooth bore without having some sort of wad attached. I have tried all kinds of tricks (when designing in SolidWorks CG is calculated on the fly) You can add a hollow base, but only to a certain depth, then CG will move backwards again. You can make the skirt thinner, but this will weaken the base. You can go for a flat nose design (wadcutter), but this will create a poor aerodynamic flow and cause the slug to tumble at some point down range.

This curly headed airgun guy has a pretty good explanation on the difference pellet designs and why they need different twist to perform well. Of course this is not smooth bore guns but it's still quite interesting:

https://www.youtube.com/watch?v=Ur6iIcVhHmM

I'm still trying to find some time to test my latest HighSpeed & LightWeight SuperSonic (TM) slug design. Any day now...

[popper]

MOAB's grid fin is actually a bunch of 'vertical' stabilizers that are steered by angle off the perpendicular quadrant. Low friction so fps is not reduced. Doesn't change the C.P. merely the torque applied. Side fins prevent rotation so the guidance system works. Many ordnance use the grid fin as it only requires rotational movement - force on it is not increased as angle of attack type fins. LEGAP used fixed rear fins with canard 'swivel' head fins for steering. The 'curly' headed guy talked about over stabilization which is really the angle of attack increase (due to gyro effect) and vertical air movement creating torque around the CG - CP does move in this case. So for long range twist, you want the CP moving toward the CG to reduce torque. Rockets on the other hand, CG changes and should move toward the CP which doesn't change in 'powered' flight. All projectiles are 'drag' stabilized, WC have the force applied at the nose, VLD is an attempt to move the 'drag' back to the rear. Attached 'wads' create 'drag' at the rear.

[W.R.Buchanan]

This just keeps getting better everyday. I am actually learning stuff I didn't know. Keep going!

Randy

[longbow]

I am still a Brenneke Classic fan, largely because they work well and because, potentially anyway, I can make them at home. The main problem I have had is maintaining the integrity of the wad column/attached wad.

I have not tried dense felt yet but will be ordering supplies shortly so both felt wads and BPI plastic "gas seals":

https://www.ballisticproducts.com/HB12-12ga-x-8mm-Wad-Base-250_bag/productinfo/072HB12/

will be included. I think I'd have to stack 2 of those to have enough attached wad.

Talking smoothbore here.

Now a question or two for the smart guys:

- just how much back of CG should CP be for good drag stabilization?
- can you add too much of a good thing? As in is there a maximum recommended attached wad length for stability? (and of course we're talking about something that will fit into a 2 3/4" hull, not an arrow). turbo posted recommended diameter to length proportions for sll lead HB slugs and attached wad slugs but I don't know the source or if entirely true ~ Hammerhead answer again.
- is an attached wad detrimental to rifled gun accuracy? Brenneke claims their Classic and other attached wad slugs are good in rifled guns too. Hmmmm, I guess if Hammerhead slugs are accurate from rifled guns then maybe I've answered my own question.

Mihec made a full bore version of the Lyman 525 gr. sabot slug but I haven't seen any range reports so no idea how accuracy is.

I do have to say that in my experience loading RB's and slugs into shotcups for smoothbore is easier than building wad columns and seems to give me better accuracy... with the exception of 0.735" RB which equals accuracy of RB in shotcup loads. I have had better results using slugs in shotcups than full bore slugs though. I think due to added guidance into the forcing cone/bore and also by protecting the slug from damage bouncing off the forcing cone.

Longbow

PS: Randy, I've been "learning about slugs for about 40 years and still apparently don't know much except it appears that the simple lead slug is smarter than I am!

[Cap'n Morgan]

Now a question or two for the smart guys:

- just how much back of CG should CP be for good drag stabilization?
- can you add too much of a good thing? As in is there a maximum recommended attached wad length for stability? (and of course we're talking about something that will fit into a 2 3/4" hull, not an arrow). turbo posted recommended diameter to length proportions for sll lead HB slugs and attached wad slugs but I don't know the source or if entirely true ~ Hammerhead answer again.
- is an attached wad detrimental to rifled gun accuracy? Brenneke claims their Classic and other attached wad slugs are good in rifled guns too. Hmmmm, I guess if Hammerhead slugs are accurate from rifled guns then maybe I've answered my own question.



I copy pasted this from the patent papers on the Vitt slug:

https://patents.google.com/patent/US3200751A/en

With reference to FIG. 8, these factors are the location of the center of gravity CG and the relative location of the center of pressure CP. Actual reduction to practice, shows that the optimum distance along the central axis between the nose of the slug and CG in proportion to the total length of the slug must be a minimum of 0.25 and a maximum of 0.35 of said total length. Cooperating with such favorable location of CG, the center of pressure CP must lie on the central axis far enough behind the CG to assure head-on stability of the slug during the short interval of time before the gyroscopic effect takes over. This separation between CG and GP for the 12 gauge slug, for example, must be from 0.3 to 0.4 inch, and the ratio between the dimension of this separation and the total length of the slug must be between a minimum of 0.15 and a maximum of 0.22 for any gauge or caliber of shotgun slugs.

[longbow]

Cap'n Morgan... you are the man! Again! Thanks for that. If I had a half a brain I guess I could have searched and found that but years of 12 ga. recoil have left me with somewhat less than half a brain.

I did search after reading that and found some other interesting info but that patent had the most info on CP and CG.

I believe I will re-initiate my intent to steal Wilhelm Brenneke's thunder... or George Vitt's thunder (very similar design to Brenneke). I've just sized down 30 1 oz. Lee slugs and made forms for hot melt glue skirts. This worked well on as cast Lee slugs before but they were hard to line up in the form due to taper and the glue was a bit messy at the tail end of the slug due to gap. if I was a better machinist I guess I would have made a tapered "socket" to suit the slug then the skirt would have matched up in diameter.

The sized slugs are straight sided so no problem to match up the glue skirt.

I will now do a bit of research and apply the CP/CG info to the design.

Longbow

[Ranch Dog]

Woow... great information. Been tied up a bit with family, but very interesting.

I've gone on to a full-bore/groove bullet and Sabot Technologies Thunderheads; mold and sabot columns for now.

[popper]

So basically a push-pin shaped plastic part that attaches to the cast slug via a shaft through the middle of the slug and is rivited at the front?