Spur ?

[azmntman]

Not being an accomplished caster I wonder...if the ball has a spur and is not loaded 1000% perfectly centered wouldn't the spur try to throw the ball of center? Kinda like a shot gun shell with a BB and a string :redface: Seems it would wobble till it straightened itself out?

NOT A Physicist!

 

[M. De Land]

I think you mean sprue, No?
Sprue concentric probably does have some effect on rotational stability but I have never been able to tell if it does or not both in ball or bullet and I shoot a lot of both, mostly cast personally.
I can't tell a lick of difference in accuracy between bought swagged balls and my home cast.
Now a bugger on the base edge of a bullet will show up very quickly in poor accuracy but a bullet nose can be quite banged up and still shoot into the same group as perfect ones.

 

[csitas]

I assume you are talking about the sprue. This is what's left from filling the mold. On real good fitting molds the sprue is rather small. I have also seen them quite large. I won't use that mold. As far as the sprue affecting accuracy , I think so . I probally don,t shoot well enough to tell but, I've heard it a thousand times to keep the sprue centered or else. I just do it cause. Also ,when quick starting ,I see most of the time ,with a proper fitting starter, that the sprue will be fattened pretty good.

 

[wulf]

Hi...I made a fixture for my drill press that
rolls the balls and gets rid of the sprue...
that way i don't have to put the ball any special
way on the patch.....quick and easy. At the range
I can only shoot in matches and score very well.
Wulf

 

[curator]

The "sprue" may have little effect aerodynamically, but if there is a void in the ball formed during casting, it will be directly under the sprue. That is the primary reason the sprue should be centered when the ball is loaded. A ball rotating around the void will have no issues with rotational velocity. On the other hand when folks eliminate the sprue, they occasionally have unexplained fliers caused when the ball rotates around a void which in not centered. Imagine your front tire lost a wheel weight at 60 mph on the interstate. Keep in mind a round ball from a 1 in 48' twist barrel is spinning at 1800 RPM when driven to 1200 fps.

 

[ghostdncr]

I think an off-center sprue would be detrimental to accuracy, but the question is "by how much, and would we be able to notice it?" With my meager shooting abilities, I get the sprue close to centered and let fly. So far, I can't complain about the results.

I believe there is much more accuracy to be had (or lost!) with properly fitted and lubricated patching than worrying over the sprue. I'm not aware of any effective way to accurately align the sprue anyway, but there is much we can do to control our patching.

 

[M. De Land]

With a 1 in 48 twist the ball makes .25 revolutions per foot. The muzzle velocity is 1200fps so .25 x1200 = 300 revolutions per second x 60seconds in a minute = 18,000 Revolutions per minute (RPM).

 

[curator]

MD: Thanks for the correction! Spell check doesn't fix typing errors or a missing "0".

 

[don hepler]

I'm thinking, that's the reasoning behind rifling. The ball or projectile, is rotating, not rolling and that gives it a gyro effect and causes it to spin more accurately. As it slows down and even before that, I would think that it would effect velocity.

Just guessing.

 

[M. De Land]

I am always calling things by the wrong name but usually it's descriptive enough for folks to figure out what I'm talking about just as you did, which is really the point.
I appreciate folks helping me out with the proper terms and figured you might as well.

 

[Eterry]

I read recently where the sprue can cause aerodynamic issues if facing the muzzle, but if off center can cause the shot to fly wild. So the consensus was to try to center facing the muzzle and be done.

Btw, the new Lee molds leave little to no sprue, which was surprising to me.

 

[hanshi]

I cast virtually all my ball using Lee molds and there is no sprue with Lee molds. I always seat "sprue" up - I can see it that way. But since I often tumble them I usually can't find where the sprue was. Even when not tumbled it's still difficult to locate.

 

[Zonie]

IMO, yes, a sprue left on the ball can try to effect the flight of the roundball.

It will have some success if the roundball is fired out of a smoothbore but fired in a rifled barrel, its effect will be almost nothing.

Some of the effect is due to the added weight and some is due to the aerodynamic forces caused by of the shape.

Lets say the forces are trying to make the ball turn to the right.
If the ball is fired out of a smooth bore and it is not spinning, the ball will be deflected to the right.

Now, if the same ball is fired in a rifled bore, as soon as it leaves the muzzle the ball starts to turn right but immediately the ball has rotated and now it is trying to force the ball down and to the right. Then as it rotates further it is trying to force the ball straight down followed by a further rotation and a corosponding force down & left, left, up & left, up, up & right and so forth.

The final result of this is the rotation causes the force to rapidly be directed in all directions so the forces cancel themselves out and the ball flies, true to the target.

 

[mooman76]

I'm thinking it won't really effect it that much unless you are a bench shooter but it's easy to find out instead of just asking opinions. Purposely load some and shoot. Then load some with the sprue up or down and compare.

 

[Wes/Tex]

I'm thinking, that's the reasoning behind rifling. The ball or projectile, is rotating, not rolling and that gives it a gyro effect and causes it to spin more accurately. As it slows down and even before that, I would think that it would effect velocity.

Just guessing.

Without getting into the tedious world of ballistic coefficient and cross-sectionally density, basically a round ball is the worst projectile shape short of a cube. Briefly, it's no longer than it is tall or wide, so it sheds velocity quicker than any longer projectile shape. Within its usable range though, it's an effective projectile and the heavier it is the better it performs at distance. Knowing these limitations was one of those things we all accepted 40 or 50 years ago when muzzleloading became popular again and especially for hunting.

 

[M. De Land]

Actually a ball in flight is not really a sphere at all as it has a parallel waist band from loading pressure and set back (obturation).
If this shape were to tumble I think it would be horribly inaccurate but rotation and the shape itself makes it aerodynamically stable, apparently.

 

[M. De Land]

MY guess is this banded sphere shape is why a smooth bore can be so accurate to 50-75 yards but after that it needs rotation to maintain the same cone of dispersion.

 

[azmntman]

IMO, yes, a sprue left on the ball can try to effect the flight of the roundball.

It will have some success if the roundball is fired out of a smoothbore but fired in a rifled barrel, its effect will be almost nothing.

Some of the effect is due to the added weight and some is due to the aerodynamic forces caused by of the shape.

Lets say the forces are trying to make the ball turn to the right.
If the ball is fired out of a smooth bore and it is not spinning, the ball will be deflected to the right.

Now, if the same ball is fired in a rifled bore, as soon as it leaves the muzzle the ball starts to turn right but immediately the ball has rotated and now it is trying to force the ball down and to the right. Then as it rotates further it is trying to force the ball straight down followed by a further rotation and a corosponding force down & left, left, up & left, up, up & right and so forth.

The final result of this is the rotation causes the force to rapidly be directed in all directions so the forces cancel themselves out and the ball flies, true to the target.

Thanks Zonie, that makes since.

And BTW I was just wondering, cant make enough difference for my style (3-4" at 90 yards and the guns a keeper!)

 

[don hepler]

I get what you're saying, I was just thinking that a ball with a sprue, might be more affected, than a total smooth round ball.

True round ball not best coefficient.