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Old November 3, 2008, 10:56 PM   #1
T.A.Sharps
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Foster Slug Truth

Quote:
Originally Posted by T.A.Sharps

I checked my ballistics book, I will sum up what it says about foster slugs (if you want to read it exactly, order the book, or check your book store to see if they have it in, its on pg.307):

A Foster slug's groves that are molded into it provides a very slight spin, but the accuracy gained from the amount of gyroscopic stability is very little.

Research by Winchester shows that the turn rate of a foster slug is 1 turn in 24 feet.

Slugs without the groves still hit nose first without tumbling, but the grooves do give better accuracy over a non-grooved slugs.


1 in 24ft
vs 1 in 24inches spin of a sabot round from a rifled barrel shotgun.
I am posting this here because I know there is a long debate about if a foster slug spins from the "rifling" or not, making it more accurate or not. I have been on both sides of the argument at different times based on things I have heard and read.

However I forgot that I have a book on firearm ballistics. Some of you may have seen it, "Understanding Firearm Ballistics" by Robert A. Rinker.

I originally posted this in another thread, but I thought it might be useful to everyone as a main topic.
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Old November 4, 2008, 12:32 AM   #2
Ricky B
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Here is what Wikipedia has to say on the subject (with my comments in Italics):
The defining characteristic of the Foster slug is the deep hollow in the rear, which places the center of mass very near the tip of the slug, much like a shuttlecock. If the slug begins to tumble in flight, drag will tend to push the slug back into straight flight. This gives the Foster slug stability and allows for accurate shooting out to ranges of about 75 yards (about 70 meters). Most Foster slugs also have "rifling", which consists of thin fins on the outside of the slug. Contrary to popular belief, these fins actually impart no spin onto the slug as it travels through the air. Since the slug is fired at a supersonic velocity, the nose of the slug pushing a shockwave creates a vacuum on the side of the slug, where the fins are located [and thus no aerodynamic effect from the fins since there is no (or little) air around the fins, at least while traveling at supersonic speeds]. The actual purpose of the fins is to allow the slug to safely be swaged down when fired through a choke [and thus be centered in the barrel throughout its travel through the bore], although accuracy will suffer when such a slug is fired through tighter chokes.
What I've read elsewhere is to similar effect.
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Old November 4, 2008, 12:34 PM   #3
fxdrider
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2 days ago I brought my Winchester 1300 12 gauge Slug Hunter to the range to see how accurate I could be with it. Brought along my Improved Cylinder choke tube and 3 boxes of Winchester 2 3/4" Rifled slugs. These are the kind of slugs you were talking about - just regular sugs with the "fins", no sabot, shot out of a 22" smoothbore barrel, open sights(no scope). The results? 5 rounds into 4 1/2 " at 100 yards. I don't know if the fins help or hurt accuracy, or if they put any kind of spin on the projectile or not. I just know that 4 1/2" groups at 100 yards is accurate enough to kill deer where I hunt.

Now I just need to find some of those deer.
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Old November 4, 2008, 04:20 PM   #4
T.A.Sharps
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As far as I am concerned there is no room for debate after a book written on ballistics reports the actual physics of a foster slug in flight.

If you get 4" groupings at 100 yards that is awesome.

There are other aspects of the foster slug that the book talks about that I don't want to type out here, such as velocity and effective range.

Wikipedia is hardly a reputable source of information, especially since any moron can edit the information on it.
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Old November 4, 2008, 04:33 PM   #5
TheManHimself
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The way I always understood it, the main purpose of the fins on a rifled slug is to give the lead space to compress into if you fire them through a choke tighter than cylinder, so you don't damage the choke tube or barrel. I could be wrong though.
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Old November 4, 2008, 08:44 PM   #6
L_Killkenny
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Sharps, I'll argue with the book.

I'm not a ballistics expert and I didn't sleep at a Holiday Inn last night. But I am experience hunting and shooting with foster slugs and I'm here to tell you that with decent optics a foster slug is accurate enough for deer hunting well BEYOND 75 yards. If you give me or most hunters here in Iowa a slug gun with a scope, some very basic ballistic knowledge and a standing deer at 125 yards is a dead deer and you will fill the freezer with one shot. Argue with that.

LK
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Old November 4, 2008, 11:40 PM   #7
Scattergun Bob
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L_Killkenny

I think it was Ricky B quoting Wikipedia that suggested 75 yards! I sure wish we could quote GUN data sites in the future not Wikipedia. I think T.A. Sharps quoted 4" @ 100 yards as being awesome.

Here is my take on this matter, after extensive testing, smooth bore shotgun barrels all respond differently and a new barrel that one tests may or may not get groups the size you need. Different barrel and slug combinations make huge differences in group size. That said, I have tested barrels that shot 1 hole groups at 50 yrds and barrels that shot +4" at 50 yrds. I have no problem believing deer kills at 125 yrds with good barrels and scoped slug guns. I haven't had to shoot past 60 yrds for hogs or deer yet.

Good Luck & be Safe
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Last edited by Scattergun Bob; November 5, 2008 at 12:46 PM.
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Old November 5, 2008, 12:05 AM   #8
Ricky B
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Debate? What debate?

The quote from Wikipedia was not to vouch for or assert the 75-yard claim but to show that there was agreement that the fins don't provide accuracy by spinning the projectile. In that regard, the Wikipedia article supports the book.
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Old November 5, 2008, 12:07 AM   #9
Ricky B
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I sure wish we could quote GUN data sites in the future not Wikipedia.

You are free to do so. Nothing is stopping you.
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Old November 5, 2008, 12:16 AM   #10
Scattergun Bob
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I do use better sources, I was speaking in the collective we. But I will be specific as say YOU Ricky sould find a better source for your information.
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Old November 5, 2008, 12:28 AM   #11
Ricky B
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Advice duly noted.
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Old November 5, 2008, 09:04 PM   #12
T.A.Sharps
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Quote:
Originally Posted by L_KillKenny
Sharps, I'll argue with the book.
Really?

You are going to argue with a scientific publication involving more history, research, and testing on the physics of ballistics and firearms than you could have researched in 2 life times?

Based on your "Hill Billy Logic" of you shot a deer every year with a slug?

Oh, ok.

Whatever numbers people are talking about aside, that is just pure ignorance. I hunt in Iowa too, It hardly takes years of experience to fill a tag during shotgun season. I made no mention of if you could or couldn't kill a deer at any specific range, nor did I mention any group sizes you could get at any range.

In fact, I was not making any opinionated statements, accept I thought a 4" grouping @ 100yds with fosters is awesome. I was reporting on the factual physics of a foster slug in flight.
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Old November 5, 2008, 09:23 PM   #13
BuckHammer
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Quote:
Originally Posted by Ricky B
Contrary to popular belief, these fins actually impart no spin onto the slug as it travels through the air. Since the slug is fired at a supersonic velocity, the nose of the slug pushing a shockwave creates a vacuum on the side of the slug, where the fins are located [and thus no aerodynamic effect from the fins since there is no (or little) air around the fins, at least while traveling at supersonic speeds]
I have no doubt that the air does nothing to make the foster slug spin, but does the contact of the fins on the barrel have an effect?
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Old November 5, 2008, 10:04 PM   #14
Dave McC
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A couple things...

I've at least 30 deer slain with slugs behind me. Best guess, Brenekkes for about 1/3 of them, Forsters for the rest.

My two slug shooters are 870s, with extension mags, peep sights, short barrels, good triggers and well developed sets of wear marks.

No, I don't need a lot of rounds in those mag extensions. I found out decades back, tho, that clamping the barrel to the extension stiffens it and makes the vibrations more uniform.

The best slug here and now for these two is the KO Brenekke 1 oz. This is the first time ever where both guns "Liked" the same slug.

One gun has a 18" barrel, the other a 20". The 20" barrel takes Remchokes and has a rifled tube screwed in for deer season. The other is chokeless.

Both barrels have extended forcing cones, no overbores or ports.

The 18" barreled one has been mine since 1959. It was made in 1950, first year of production.Worked into a practical gun ca 1980.

3 shot, 100 yard groups from the bench and sandbags run less than 5" ETE.

The 20" barrelled version is a rebuilt police gun with RS/RC barrel.

It sticks them under 4" ETE.

Note that I have plenty of experience, a PAST wearable recoil pad and good bench technique.

Typically, field shots for me on MD's Eastern Shore run less than 50 yards. Average is about 30.

HTH....
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Old November 5, 2008, 10:10 PM   #15
musher
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Quote:
The actual purpose of the fins is to allow the slug to safely be swaged down when fired through a choke
Well if that's so, why do they trouble to put the 'fins' in a helical pattern?
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Old November 5, 2008, 10:19 PM   #16
hogdogs
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Cuz they couldn't market them as "rifled slugs" if they were straight. They also may have intended for the aero spin to actually be much greater and left the shape alone as it looked cooler.
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Old November 5, 2008, 10:20 PM   #17
L_Killkenny
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Like I said, my observations are just that, observations. I've shot foster slugs from 5 or 6 smoothbores and seen them shot/used from many times that number. All I can say is I've yet to see a smoothbore not shoot at least "paper plate" size groups at 100 yards with ammo it likes. Mine shoots around 5". And no, it isn't that hard to find deer to shoot here in Iowa but I've shot or seen shot enough one-shot kills beyond 100 yards with foster slugs to prove to me it's not just luck.

Now, I can't argue with how much the grooves/fins help it spin but it must be enough. From the information I've see/heard in the past, smoothbore muskets of a couple centuries ago that would do well to shoot 2 ft groups at 100 yards. There has to be a reason slug gun's with foster slugs are more accurate.

Does your book tell us what that is?

LK
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Old November 5, 2008, 10:37 PM   #18
hogdogs
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Killkenny, The reason a modern slug is accurate is because it is not a round ball. It is a severly nose heavy projectile. If you want to see how one works in slow motion, watch a badminton game. The shuttle cock actually reverses direction and still remains extremely accurate at low speed with no intended spin.
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Old November 6, 2008, 12:24 AM   #19
Ruger4570
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You are going to argue with a scientific publication involving more history, research, and testing on the physics of ballistics and firearms than you could have researched in 2 life times?

You sure look like someone just dying to get into a fight.

I can't see, but WHO is the WORLDS most scientific author you quote?? I am curious as to who he is and how his writing has become the world standard for fact. Is it that Robert Rinker fellow? If so, I have to admit, I have read just about everything published and I don't recall his name being thrown out there as some "expurt"

Just to be fair, I have done just a bit of actual research on not only Fosters, but various sabot slugs. I was doing a free lance article and I received 100's of slugs from the various manufactures.
I was beyond careful in my testing, mostly with sabots, but many Foster types.
I used an Ithaca Deerslayer, Remington 870, Remington 1100 and a Mosberg all with scopes in testing Fosters. Depending on the brand, in the Ithaca, the rifling was compressed to ,,, like gone. The gun still outshot all other guns. Why, because Ithaca bored out their barrels small and precisely uniform from one end to another.
Different brands of slugs are made in different diameters so an arguement based on rifling depth is hardly argueable.
There was NO rifling to consider on recovered Ithaca slugs, so the rifling contributed NOTHING to the accuracy, nor was there any rifling left to impart a spin. How could that be?
If you look at the situation with a half open mind, you should be able to see, the depth of the rifling on a slug would have no real impact on spinning the slug. I would be surprised at the 1 in 24 feet spin in fact.
Slugs simply fly somewhat accurately based on the heavy nose principle as exhibited by darts, arrows, spears and badmitton birds.

I also have to laugh at the statement, the Author of your book, a single individual, had MORE reaseach in the book than SOMEONE else could achieve in 2 LIFETIMES???

Comic relief right??
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